diff --git a/IMPORTS.json b/IMPORTS.json
index 33e34aa..389278e 100644
--- a/IMPORTS.json
+++ b/IMPORTS.json
@@ -18,8 +18,8 @@
     {
       "project": "YoloRuntime",
       "directory": "YoloRuntime",
-      "source_head": "df794f144df90d867f6ec4ec94c55eb3435e1a83",
-      "source_tree": "93f2652c042bbc68079935c49c59de44b928137f",
+      "source_head": "9be44d557eb05c2fab5fd8f69974a6101532cc7c",
+      "source_tree": "395864996ded1983011a3c9375fce0537295dcd8",
       "working_source_snapshot": false
     }
   ]
diff --git a/YoloRuntime/CMakeLists.txt b/YoloRuntime/CMakeLists.txt
index 56882eb..01cdf09 100644
--- a/YoloRuntime/CMakeLists.txt
+++ b/YoloRuntime/CMakeLists.txt
@@ -10,13 +10,36 @@ set(CMAKE_C_STANDARD 11)
 set(CMAKE_C_STANDARD_REQUIRED ON)
 set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
+# Robust contour fitting uses the same OpenCV core/imgproc implementation as MatchVerify.
+if(WIN32 AND NOT OpenCV_DIR AND EXISTS "E:/06_EnvConfig/opencv/build/x64/vc16/lib")
+    set(OpenCV_DIR "E:/06_EnvConfig/opencv/build/x64/vc16/lib" CACHE PATH "OpenCV package")
+endif()
+if(NOT WIN32 AND NOT OpenCV_DIR AND RKNN_MODEL_ZOO_ROOT AND
+   EXISTS "${RKNN_MODEL_ZOO_ROOT}/3rdparty/opencv/opencv-linux-aarch64/share/OpenCV")
+    set(OpenCV_DIR "${RKNN_MODEL_ZOO_ROOT}/3rdparty/opencv/opencv-linux-aarch64/share/OpenCV")
+endif()
+find_package(OpenCV REQUIRED COMPONENTS core imgproc)
+
 add_library(yolo_runtime SHARED
+    src/yolo_mask_ids.cpp
     src/yolo_runtime.cpp
     src/yolo_seg_geometry.cpp)
 target_include_directories(yolo_runtime
     PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include> $<INSTALL_INTERFACE:include>
     PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src)
 add_library(YoloRuntime::Runtime ALIAS yolo_runtime)
+target_include_directories(yolo_runtime PRIVATE ${OpenCV_INCLUDE_DIRS})
+target_link_libraries(yolo_runtime PRIVATE ${OpenCV_LIBS})
+if(WIN32)
+    foreach(opencv_target IN LISTS OpenCV_LIBS)
+        if(TARGET ${opencv_target})
+            add_custom_command(TARGET yolo_runtime POST_BUILD
+                COMMAND ${CMAKE_COMMAND} -E copy_if_different
+                    $<TARGET_FILE:${opencv_target}> $<TARGET_FILE_DIR:yolo_runtime>
+                VERBATIM)
+        endif()
+    endforeach()
+endif()
 set_target_properties(yolo_runtime PROPERTIES EXPORT_NAME Runtime)
 find_package(Threads REQUIRED)
 if(WIN32)
@@ -148,6 +171,9 @@ endif()
 
 if(YOLO_RUNTIME_BUILD_CONTRACT_TESTS)
     enable_testing()
+    add_executable(yolo_mask_ids_test tests/mask_ids_test.cpp)
+    target_link_libraries(yolo_mask_ids_test PRIVATE yolo_runtime)
+    add_test(NAME yolo_mask_ids_test COMMAND yolo_mask_ids_test)
     add_executable(yolo_runtime_c_api_contract tests/c_api_contract.c)
     target_include_directories(yolo_runtime_c_api_contract PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include)
     target_link_libraries(yolo_runtime_c_api_contract PRIVATE yolo_runtime)
@@ -175,7 +201,13 @@ if(YOLO_RUNTIME_BUILD_CONTRACT_TESTS)
         tests/seg_geometry_test.cpp
         src/yolo_seg_geometry.cpp)
     target_include_directories(yolo_seg_geometry_test PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src)
+    target_include_directories(yolo_seg_geometry_test PRIVATE ${OpenCV_INCLUDE_DIRS})
+    target_link_libraries(yolo_seg_geometry_test PRIVATE ${OpenCV_LIBS})
     add_test(NAME yolo_seg_geometry_test COMMAND yolo_seg_geometry_test)
+    add_executable(yolo_runner_mask_output_test tests/runner_mask_output_test.cpp)
+    target_include_directories(yolo_runner_mask_output_test PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/src ${CMAKE_CURRENT_SOURCE_DIR}/include)
+    add_test(NAME yolo_runner_mask_output_test COMMAND yolo_runner_mask_output_test)
     add_executable(yolo_runner_label_layout_test tests/runner_label_layout_test.cpp)
     target_include_directories(yolo_runner_label_layout_test PRIVATE
         ${CMAKE_CURRENT_SOURCE_DIR}/include
@@ -209,6 +241,11 @@ if(WIN32)
         "${ONNXRUNTIME_ROOT}/runtimes/win-x64/native/onnxruntime_providers_shared.dll"
         DESTINATION lib)
     install(FILES "${ONNXRUNTIME_ROOT}/ThirdPartyNotices.txt" DESTINATION licenses)
+    foreach(opencv_target IN LISTS OpenCV_LIBS)
+        if(TARGET ${opencv_target})
+            install(FILES $<TARGET_FILE:${opencv_target}> DESTINATION lib)
+        endif()
+    endforeach()
 else()
     install(TARGETS yolo_runtime rk3588_yolo_runner EXPORT YoloRuntimeTargets
         RUNTIME DESTINATION .
diff --git a/YoloRuntime/README.md b/YoloRuntime/README.md
index a5302c7..fd5821e 100644
--- a/YoloRuntime/README.md
+++ b/YoloRuntime/README.md
@@ -2,8 +2,9 @@
 
 Shared C++17 Runtime, C ABI 5, for Windows x64 CPU and Linux AArch64 RK3588.
 This is the sole production source for Studio, its SDK packages and MatchVerify.
-Detect, CLS, Seg, OBB and Pose are retained. Seg supports minimum enclosing circle
-and minimum-area rotated rectangle; no robust-circle algorithm is added.
+Detect, CLS, Seg, OBB and Pose are retained. Seg supports four geometry modes:
+minimum-area rotated rectangle (1), minimum enclosing circle (2), rectangle mean-diameter
+circle (3), and robust contour-fit circle (4). Existing ABI 5 mode values and structure sizes remain unchanged.
 
 ## Build and consume
 
@@ -32,3 +33,53 @@ Binary hashes differ between platforms and build toolchains by design.
 
 Historical origin: RK3588_AI_Platform Runtime ABI 5 at repository HEAD
 868a5f22f00ff2c81c3d0a6d2037400f037ac924, with its working source preserved during migration.
+
+## Seg geometry modes
+
+- `YOLO_SEG_GEOMETRY_MIN_AREA_RECT`: all mask boundary points, minimum-area rotated rectangle.
+- `YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE`: all mask boundary points, minimum enclosing circle.
+- `YOLO_SEG_GEOMETRY_MEAN_DIAMETER_CIRCLE`: same rectangle center, radius `(width + height) / 4`.
+- `YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE`: largest external contour, arc-length sampling and
+  Tukey IRLS fit with quality checks, migrated from MatchVerify's tested `SegCircleGeometry::Fit`.
+  Failure returns that contour's minimum enclosing circle. `type` remains the requested fit mode;
+  inspect `fit_status` (`YOLO_SEG_FIT_SUCCEEDED` or `YOLO_SEG_FIT_ENCLOSING_FALLBACK`).
+  Other modes return `YOLO_SEG_FIT_NOT_REQUESTED`. Empty masks fail geometry calculation.
+
+`fit_status` uses the first formerly reserved geometry word; existing fields, structure size
+and ABI number remain unchanged. Query capability/mode bits before requesting a new mode
+from an older Runtime. Linux runner: `--seg-geometry rect|circle|mean|fit`; JSON includes fit status.
+
+OpenCV core/imgproc is now required to build the robust fit. Windows uses `OpenCV_DIR`;
+installation includes its matching DLL(s) in the dependency manifest. Linux builds require
+a target-compatible OpenCV package (`OpenCV_DIR`); deploy its shared dependencies as for
+the existing Seg backend. This change does not update already deployed consumer applications.
+
+
+## RGB instance-ID masks (2026-10-21)
+
+`yolo_masks_compose_rgb_ids` is an additive public C API (ABI 5 structures
+unchanged). Obtain each binary mask with `yolo_result_set_get_seg_mask`, keep
+its result set alive, and pass the mask views in the intended instance order.
+The function assigns ID = array index + 1 (not class ID), supports 0..255 masks,
+and places each mask using its original-image origin. Pass the original image
+width/height and a caller-owned RGB888 destination with its byte stride/capacity.
+No dilation, fitting, resizing, or contour filling is performed.
+
+| Membership | RGB bytes |
+|---|---|
+| Background | (0,0,0) |
+| One instance | (ID,ID,ID) |
+| Two instances | (ID1,ID2,ID1) |
+| Three instances | (ID1,ID2,ID3) |
+
+IDs in a shared pixel are ascending. Remove zero and duplicate channel values
+to decode the instance set. Holes and disconnected regions are retained.
+More than 255 instances or more than three at a pixel returns
+`YOLO_STATUS_UNSUPPORTED` with a diagnostic when an error object is supplied.
+Invalid bounds/stride/nonbinary pixels are rejected. Failure leaves the complete
+destination unchanged; successful writes leave row padding unchanged. Zero masks
+produce a black canvas. Source memory must remain readable during the call and
+must not overlap output memory. Save as a lossless RGB image; when using a BGR
+writer, convert RGB to BGR first. Existing per-instance binary-mask access and
+runner PGM exports are unchanged. Apps must explicitly adopt the new API; this
+batch does not redeploy any app or device runtime.
diff --git a/YoloRuntime/VERIFICATION.md b/YoloRuntime/VERIFICATION.md
index 09f311d..f160f60 100644
--- a/YoloRuntime/VERIFICATION.md
+++ b/YoloRuntime/VERIFICATION.md
@@ -1,8 +1,47 @@
 # Verification and consumer handoff
 
-- Public C ABI headers and geometry sources are byte-identical to the extracted Studio snapshot. Windows UTF-8 filesystem boundaries were repaired; all model weights and user samples remain outside this library.
+- Initial extraction preserved the Studio snapshot. The four-mode update below adds two geometry modes while retaining ABI 5 sizes, old field offsets, and existing mode values. All model weights and user samples remain outside this library.
 - `scripts/verify.ps1`: standalone Windows build, seven CTest contracts with Release assertions enabled, dependency negative checks, installation and an independent installed CMake consumer.
 - Native Linux: configure with RKNN backends disabled, build and run `ctest --output-on-failure` from the build directory. Seven contracts pass; this is host-native logic validation, not NPU execution.
 - Studio cross-builds the Linux AArch64 Runtime using its explicitly supplied Model Zoo. The manifest identifies ELF architecture; only matching Windows/ARM source revisions can be published together.
 - MatchVerify's scripts/verify-runtime-update.ps1 exercises both real consumer build paths against a disposable ABI-compatible source update and restores the original source dependency. SDK decoding/masks/geometry parity uses the real business sample without changing it.
 - Final current-source completion and command evidence: .codex/delivery-integrity.json. There is no physical RK3588/camera/robot acceptance and no automatic update service for already deployed programs.
+
+## Four Seg geometry modes (2026-10-21)
+
+- Scope: shared Runtime only; rectangle=1, enclosing circle=2 unchanged; mean diameter circle=3, robust fit circle=4 added. No consumer app or deployed Runtime was changed.
+- Robust fit is migrated without algorithm changes from the MatchVerify header used in the preceding 1981-target comparison. It chooses the largest external contour; failed fitting returns that contour's enclosing circle. `fit_status` reports success/fallback in a formerly reserved ABI word.
+- Windows `scripts/verify.ps1`: seven Release CTest contracts, install, dependency-manifest negative checks and independent installed C consumer pass. Synthetic tests cover non-square mean radius, origin offsets, detached noise, protrusions, elongated/point fallback and empty inputs.
+- `tests/verify_four_geometry.py`: installed public C API, four modes on rotor `10_origin.png` (22 targets) and stator `135_origin.png` (32 targets), using the preceding experiment directories as explicit `--reference` arguments. All masks match their recorded SHA256 values; rectangle/mean output exactly matches prior float results; robust fit maximum discrepancy is below 0.000061 pixel. Invalid modes 0/5 are rejected. Evidence: `build/four-geometry/four-mode-api.json`.
+- OpenCV runtime DLL deployment is included in build and installation; the initial missing-DLL test startup failure was fixed before the successful full rerun.
+- Linux runner accepts rect/circle/mean/fit and includes fit status in JSON. Linux/AArch64 rebuild and physical RK3588 validation are not performed in this batch; target-compatible OpenCV core/imgproc is required for that build.
+- Completion record and exact commands: `.codex/delivery-integrity.json`. Next consumer step is explicit selection of one of the four public modes after rebuilding against this library; it is outside this batch.
+
+## Consumer four-mode and board mask update (2026-10-21)
+
+- Runner now saves an unpadded P5 binary PGM for each Seg instance under `<output-stem>.masks/`, with relative maskPath in JSON and the unchanged mask metadata/original-image offsets. RGB/RGBA render overlays use the same class colors and alpha as Studio, before the requested geometry is drawn.
+- `yolo_runner_mask_output_test` adds padded-row/offset/hole preservation, alpha/unchanged-background and file-byte tests. Windows baseline now includes eight contracts.
+- Studio's matching ARM64 Runtime/runner build completed using the supplied Model Zoo OpenCV 3.4.5. Readelf confirms AArch64 and no external OpenCV shared-library dependency. Matching Windows/ARM manifests are checked during Studio publication. No real-device execution was performed.
+- Current consumer checkpoints: MatchVerify/SHARED_RUNTIME_HANDOFF.md and RK3588_AI_Platform/docs/codex/CURRENT_BATCH.md.
+
+
+## RGB instance-ID mask batch (2026-10-21)
+
+Scope: additive public `yolo_masks_compose_rgb_ids`; preserve existing ABI 5
+structures and per-instance masks; no dilation, consumer migration, runner
+export change, deployment, commit, push, or physical-device validation.
+Pre-existing dirty library changes are retained; baseline copies for edited
+existing files are in `build/rgb-id-mask-baseline`.
+
+Acceptance: exact background/one/two/three membership RGB rules; independent
+membership reconstruction over the full fixture canvas; holes/disconnected
+pixels, input origins and padded input/output rows; all 255 instance IDs;
+explicit four-overlap/count/binary/ABI/bounds/capacity errors with untouched
+caller output. `yolo_mask_ids_test` exercises the exported DLL function;
+`yolo_runtime_c_api_contract` calls it from C. The installed C consumer also
+calls the new symbol. Run `powershell -ExecutionPolicy Bypass -File scripts/verify.ps1`
+for the complete native build/CTest/install/manifest/consumer baseline.
+Actual completion and command evidence are in `.codex/delivery-integrity.json`.
+Next action after successful verification: consumers can pass their ordered
+mask views and original canvas size to the new API; existing applications stay
+on their current export path until separately migrated.
diff --git a/YoloRuntime/include/yolo_runtime.h b/YoloRuntime/include/yolo_runtime.h
index 4be5f2b..78270ba 100644
--- a/YoloRuntime/include/yolo_runtime.h
+++ b/YoloRuntime/include/yolo_runtime.h
@@ -17,6 +17,23 @@ extern "C" {
 typedef struct yolo_runtime yolo_runtime_t;
 typedef struct yolo_result_set yolo_result_set_t;
 
+/* Compose mask_count binary (0/255) masks into an RGB888 canvas, without dilation.
+   IDs are input index + 1 (1..255); origins locate masks on the canvas.
+   Background=(0,0,0), single=(id,id,id), two=(id1,id2,id1),
+   three=(id1,id2,id3), where id1 < id2 < id3. Remove zero/duplicate
+   channels to decode membership. Holes and disconnected regions are preserved.
+   Zero masks (masks may be NULL) produces a black canvas.
+   Caller owns output; capacity must cover (height-1)*stride + width*3 bytes.
+   Padding and the entire output on failure remain unchanged. Output must not
+   overlap mask data. More than 255 masks or >3 memberships at any pixel returns
+   UNSUPPORTED; malformed binary data/bounds return INVALID_ARGUMENT.
+   This additive API does not change the existing ABI 5 structures/interfaces. */
+YOLO_RUNTIME_API yolo_status_t yolo_masks_compose_rgb_ids(
+    const yolo_mask_view_v1_t* masks, uint32_t mask_count,
+    int32_t width, int32_t height, unsigned char* output,
+    int32_t row_stride_bytes, uint64_t output_capacity_bytes,
+    yolo_error_info_v1_t* error);
+
 YOLO_RUNTIME_API uint32_t yolo_runtime_get_abi_version(void);
 YOLO_RUNTIME_API yolo_status_t yolo_runtime_create(
     const char* config_path,
diff --git a/YoloRuntime/include/yolo_runtime_types.h b/YoloRuntime/include/yolo_runtime_types.h
index b57e9f3..f17ebe9 100644
--- a/YoloRuntime/include/yolo_runtime_types.h
+++ b/YoloRuntime/include/yolo_runtime_types.h
@@ -51,10 +51,18 @@ typedef int32_t yolo_seg_geometry_mode_t;
 #define YOLO_SEG_GEOMETRY_NONE ((yolo_seg_geometry_mode_t)0)
 #define YOLO_SEG_GEOMETRY_MIN_AREA_RECT ((yolo_seg_geometry_mode_t)1)
 #define YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE ((yolo_seg_geometry_mode_t)2)
+#define YOLO_SEG_GEOMETRY_MEAN_DIAMETER_CIRCLE ((yolo_seg_geometry_mode_t)3)
+#define YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE ((yolo_seg_geometry_mode_t)4)
+
+#define YOLO_SEG_FIT_NOT_REQUESTED 0u
+#define YOLO_SEG_FIT_SUCCEEDED 1u
+#define YOLO_SEG_FIT_ENCLOSING_FALLBACK 2u
 
 #define YOLO_CAPABILITY_INFER_IMAGE (1u << 0)
 #define YOLO_CAPABILITY_SEG_MIN_AREA_RECT (1u << 1)
 #define YOLO_CAPABILITY_SEG_MIN_ENCLOSING_CIRCLE (1u << 2)
+#define YOLO_CAPABILITY_SEG_MEAN_DIAMETER_CIRCLE (1u << 3)
+#define YOLO_CAPABILITY_SEG_ROBUST_FIT_CIRCLE (1u << 4)
 
 #define YOLO_PIXEL_FORMAT_BIT(format) (1u << (uint32_t)(format))
 #define YOLO_SEG_GEOMETRY_BIT(mode) (1u << (uint32_t)(mode))
@@ -149,7 +157,10 @@ typedef struct yolo_seg_geometry_v1 {
     float height;
     float angle_radians;
     float radius;
-    uint32_t reserved[8];
+    /* Uses the first formerly reserved word; ABI 5 size and prior fields unchanged.
+       NOT_REQUESTED for modes 1-3; SUCCEEDED or ENCLOSING_FALLBACK for mode 4. */
+    uint32_t fit_status;
+    uint32_t reserved[7];
 } yolo_seg_geometry_v1_t;
 
 typedef struct yolo_mask_view_v1 {
diff --git a/YoloRuntime/scripts/verify.ps1 b/YoloRuntime/scripts/verify.ps1
index 540a56c..8b6875d 100644
--- a/YoloRuntime/scripts/verify.ps1
+++ b/YoloRuntime/scripts/verify.ps1
@@ -18,7 +18,7 @@ find_package(YoloRuntime 5 CONFIG REQUIRED)
 add_executable(consumer main.c)
 target_link_libraries(consumer PRIVATE YoloRuntime::Runtime)
 '@ | Set-Content (Join-Path $consumer 'CMakeLists.txt') -Encoding ASCII
-'#include <yolo_runtime.h>' + "`n" + 'int main(void){return yolo_runtime_get_abi_version()==5 ? 0 : 1;}' | Set-Content (Join-Path $consumer 'main.c') -Encoding ASCII
+'#include <yolo_runtime.h>' + "`n" + 'int main(void){unsigned char rgb[3]={1,2,3}; if(yolo_masks_compose_rgb_ids(0,0,1,1,rgb,3,3,0)!=YOLO_STATUS_OK || rgb[0] || rgb[1] || rgb[2]) return 2; return yolo_runtime_get_abi_version()==5 ? 0 : 1;}' | Set-Content (Join-Path $consumer 'main.c') -Encoding ASCII
 $consumerBuild=Join-Path $root 'build/consumer'
 & cmd /d /c "call `"$vcvars`" && cmake -S `"$consumer`" -B `"$consumerBuild`" -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_PREFIX_PATH=`"$install`" && cmake --build `"$consumerBuild`""
 if($LASTEXITCODE -ne 0){throw 'Installed package consumer build failed'}
diff --git a/YoloRuntime/src/main.cpp b/YoloRuntime/src/main.cpp
index ba3198d..dc56351 100644
--- a/YoloRuntime/src/main.cpp
+++ b/YoloRuntime/src/main.cpp
@@ -1,5 +1,6 @@
 #include "yolo_runtime.h"
 #include "runner_label_layout.h"
+#include "runner_mask_output.h"
 
 #if defined(YOLO_RUNNER_IN_PROCESS)
 #include "common.h"
@@ -29,6 +30,7 @@ struct runner_result {
     yolo_rotated_rect_v1_t obb{};
     yolo_mask_view_v1_t mask{};
     yolo_seg_geometry_v1_t seg_geometry{};
+    std::string mask_path;
     std::vector<yolo_keypoint_v1_t> keypoints;
 };
 
@@ -160,19 +162,24 @@ std::string to_json(const runner_report& report, const std::string& model, const
                  << ", \"strideBytes\": " << result.mask.row_stride_bytes
                  << ", \"originX\": " << result.mask.origin_x
                  << ", \"originY\": " << result.mask.origin_y << '}';
-            json << ", \"maskPath\": \"" << escape_json(image) << "\"";
+            json << ", \"maskPath\": \"" << escape_json(result.mask_path) << "\"";
             const auto& geometry = result.seg_geometry;
             json << ", \"segGeometry\": {\"type\": \""
                  << (geometry.type == YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE
-                         ? "minimumEnclosingCircle" : "minimumAreaRectangle")
+                         ? "minimumEnclosingCircle" : (geometry.type == YOLO_SEG_GEOMETRY_MEAN_DIAMETER_CIRCLE
+                         ? "meanDiameterCircle" : (geometry.type == YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE
+                         ? "robustFitCircle" : "minimumAreaRectangle")))
                  << "\", \"centerX\": " << geometry.center_x
                  << ", \"centerY\": " << geometry.center_y;
-            if (geometry.type == YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE)
+            if (geometry.type != YOLO_SEG_GEOMETRY_MIN_AREA_RECT)
                 json << ", \"radius\": " << geometry.radius;
             else
                 json << ", \"width\": " << geometry.width
                      << ", \"height\": " << geometry.height
                      << ", \"angle\": " << geometry.angle_radians;
+            if (geometry.type == YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE)
+                json << ", \"fitStatus\": \"" << (geometry.fit_status == YOLO_SEG_FIT_SUCCEEDED
+                    ? "fitted" : "enclosingFallback") << '"';
             json << '}';
         }
         if (result.common.task == YOLO_TASK_POSE) {
@@ -216,6 +223,15 @@ bool make_image_view(const image_buffer_t& source, yolo_image_view_v1_t& view) {
 
 void render_results(image_buffer_t& image, const runner_report& report) {
     char text[128];
+    for (const auto& result : report.results) {
+        if (result.common.task != YOLO_TASK_SEG) continue;
+        const int channels = image.format == IMAGE_FORMAT_RGBA8888 ? 4 : 3;
+        const int stride = (image.width_stride > image.width ? image.width_stride : image.width)*channels;
+        if (image.format != IMAGE_FORMAT_RGB888 && image.format != IMAGE_FORMAT_RGBA8888)
+            throw std::runtime_error("Seg mask overlay requires RGB or RGBA source");
+        if (!runner_mask_output::blend(image.virt_addr,image.width,image.height,stride,channels,result.mask,result.common.class_id))
+            throw std::runtime_error("Invalid Seg mask overlay coordinates");
+    }
     for (size_t index = 0; index < report.results.size(); ++index) {
         const auto& result = report.results[index];
         const int x = std::max(0, static_cast<int>(result.bbox.x));
@@ -224,7 +240,7 @@ void render_results(image_buffer_t& image, const runner_report& report) {
         const int height = std::max(1, static_cast<int>(result.bbox.height));
         if (result.common.task == YOLO_TASK_SEG) {
             const auto& geometry = result.seg_geometry;
-            if (geometry.type == YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE)
+            if (geometry.type != YOLO_SEG_GEOMETRY_MIN_AREA_RECT)
                 draw_circle(&image, static_cast<int>(geometry.center_x), static_cast<int>(geometry.center_y),
                     std::max(1, static_cast<int>(std::round(geometry.radius))), COLOR_GREEN, 3);
             else
@@ -264,9 +280,9 @@ int main(int argc, char** argv) {
         else if (argument == "--json") json_path = argv[index + 1];
         else if (argument == "--seg-geometry") geometry_name = argv[index + 1];
     }
-    if (config.empty() || image.empty() || (geometry_name != "rect" && geometry_name != "circle")) {
+    if (config.empty() || image.empty() || (geometry_name != "rect" && geometry_name != "circle" && geometry_name != "mean" && geometry_name != "fit")) {
         std::cerr << "Usage: rk3588_yolo_runner --config model.yaml --image image.png "
-                     "[--output out.png] [--json result.json] [--seg-geometry rect|circle]\n";
+                     "[--output out.png] [--json result.json] [--seg-geometry rect|circle|mean|fit]\n";
         return 2;
     }
 
@@ -304,7 +320,8 @@ int main(int argc, char** argv) {
     options.seg_geometry_mode = info.task == YOLO_TASK_SEG
         ? (geometry_name == "circle"
             ? YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE
-            : YOLO_SEG_GEOMETRY_MIN_AREA_RECT)
+            : (geometry_name == "mean" ? YOLO_SEG_GEOMETRY_MEAN_DIAMETER_CIRCLE
+                : (geometry_name == "fit" ? YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE : YOLO_SEG_GEOMETRY_MIN_AREA_RECT)))
         : YOLO_SEG_GEOMETRY_NONE;
     yolo_result_set_t* result_set = nullptr;
     initialize(error, YOLO_ERROR_INFO_VERSION);
@@ -319,7 +336,25 @@ int main(int argc, char** argv) {
         yolo_runtime_destroy(runtime);
         return 4;
     }
-    render_results(source, report);
+    try {
+        const auto directory = fs::path(json_path).parent_path() / (fs::path(output).stem().string()+".masks");
+        for (size_t i=0;i<report.results.size();++i) {
+            auto& result=report.results[i];
+            if(result.common.task!=YOLO_TASK_SEG) continue;
+            fs::create_directories(directory);
+            const std::string filename="mask_"+std::to_string(i+1)+".pgm";
+            if(!runner_mask_output::save(directory/filename,result.mask))
+                throw std::runtime_error("Cannot save instance mask");
+            result.mask_path=(directory.filename()/filename).generic_string();
+        }
+        render_results(source, report);
+    } catch (const std::exception& e) {
+        std::cerr << e.what() << '\n';
+        yolo_result_set_release(result_set);
+        std::free(source.virt_addr);
+        yolo_runtime_destroy(runtime);
+        return 5;
+    }
     if (write_image(output.c_str(), &source) < 0) {
         yolo_result_set_release(result_set);
         std::free(source.virt_addr);
diff --git a/YoloRuntime/src/runner_mask_output.h b/YoloRuntime/src/runner_mask_output.h
new file mode 100644
index 0000000..44368cf
--- /dev/null
+++ b/YoloRuntime/src/runner_mask_output.h
@@ -0,0 +1,31 @@
+#pragma once
+#include "yolo_runtime_types.h"
+#include <filesystem>
+#include <fstream>
+#include <algorithm>
+#include <cstdint>
+
+namespace runner_mask_output {
+inline bool save(const std::filesystem::path& path, const yolo_mask_view_v1_t& mask) {
+    if (!mask.data || mask.width <= 0 || mask.height <= 0 || mask.row_stride_bytes < mask.width) return false;
+    std::ofstream file(path, std::ios::binary);
+    file << "P5\n" << mask.width << ' ' << mask.height << "\n255\n";
+    for (int y=0; y<mask.height; ++y)
+        file.write(reinterpret_cast<const char*>(mask.data + size_t(y)*mask.row_stride_bytes), mask.width);
+    return bool(file);
+}
+inline bool blend(unsigned char* image, int width, int height, int stride, int channels,
+                  const yolo_mask_view_v1_t& mask, int class_id) {
+    if (!image || channels < 3 || channels > 4 || width <= 0 || height <= 0 || stride < width*channels ||
+        !mask.data || mask.width <= 0 || mask.height <= 0 || mask.row_stride_bytes < mask.width ||
+        mask.origin_x < 0 || mask.origin_y < 0 || mask.width > width-mask.origin_x || mask.height > height-mask.origin_y) return false;
+    const unsigned char palette[][3]={{0,220,120},{0,170,255},{255,120,0},{220,60,220}};
+    const auto& color=palette[(class_id%4+4)%4];
+    for(int y=0;y<mask.height;++y) for(int x=0;x<mask.width;++x) {
+        if(!mask.data[size_t(y)*mask.row_stride_bytes+x]) continue;
+        auto* pixel=image+size_t(y+mask.origin_y)*stride+(x+mask.origin_x)*channels;
+        for(int c=0;c<3;++c) pixel[c]=static_cast<unsigned char>((pixel[c]*155+color[c]*100+127)/255);
+    }
+    return true;
+}
+}
diff --git a/YoloRuntime/src/yolo_mask_ids.cpp b/YoloRuntime/src/yolo_mask_ids.cpp
new file mode 100644
index 0000000..d4fdd9e
--- /dev/null
+++ b/YoloRuntime/src/yolo_mask_ids.cpp
@@ -0,0 +1,65 @@
+#include "yolo_runtime.h"
+#include <cstdio>
+#include <cstring>
+#include <exception>
+#include <limits>
+#include <vector>
+
+extern "C" yolo_status_t yolo_masks_compose_rgb_ids(
+    const yolo_mask_view_v1_t* masks, uint32_t count,
+    int32_t width, int32_t height, unsigned char* output,
+    int32_t stride, uint64_t capacity, yolo_error_info_v1_t* error) {
+    if (error && (error->struct_size < sizeof(*error) || error->version != YOLO_ERROR_INFO_VERSION))
+        return YOLO_STATUS_ABI_MISMATCH;
+    const auto finish = [error](yolo_status_t status, const char* message) {
+        if (error) {
+            error->status = status;
+            std::snprintf(error->message, sizeof(error->message), "%s", message);
+        }
+        return status;
+    };
+    if (count > 255) return finish(YOLO_STATUS_UNSUPPORTED, "RGB instance IDs support at most 255 masks");
+    if (!output || (count && !masks) || width <= 0 || height <= 0 || stride <= 0 ||
+        uint64_t(width)*3 > uint64_t(stride))
+        return finish(YOLO_STATUS_INVALID_ARGUMENT, "Invalid RGB canvas or mask array");
+    const uint64_t required = uint64_t(height-1)*uint64_t(stride) + uint64_t(width)*3;
+    const uint64_t packed_size = uint64_t(width)*uint64_t(height)*3;
+    if (required > capacity || required > std::numeric_limits<size_t>::max() ||
+        packed_size > std::numeric_limits<size_t>::max())
+        return finish(YOLO_STATUS_BUFFER_TOO_SMALL, "RGB output capacity is too small");
+    for (uint32_t i=0; i<count; ++i) {
+        const auto& m = masks[i];
+        if (m.struct_size < sizeof(m) || m.version != YOLO_MASK_VIEW_VERSION)
+            return finish(YOLO_STATUS_ABI_MISMATCH, "Incompatible mask view");
+        if (!m.data || m.width <= 0 || m.height <= 0 || m.row_stride_bytes < m.width ||
+            m.origin_x < 0 || m.origin_y < 0 || m.origin_x > width || m.origin_y > height ||
+            m.width > width-m.origin_x || m.height > height-m.origin_y ||
+            uint64_t(m.height-1)*uint64_t(m.row_stride_bytes)+uint64_t(m.width) > std::numeric_limits<size_t>::max())
+            return finish(YOLO_STATUS_INVALID_ARGUMENT, "Invalid mask bounds or row stride");
+    }
+    try {
+        std::vector<unsigned char> rgb(static_cast<size_t>(packed_size), 0);
+        for (uint32_t i=0; i<count; ++i) {
+            const auto& m = masks[i];
+            const auto id = static_cast<unsigned char>(i+1);
+            for (int32_t y=0; y<m.height; ++y) {
+                const auto* row = m.data + size_t(y)*m.row_stride_bytes;
+                for (int32_t x=0; x<m.width; ++x) {
+                    if (!row[x]) continue;
+                    if (row[x] != 255)
+                        return finish(YOLO_STATUS_INVALID_ARGUMENT, "Mask pixels must be 0 or 255");
+                    auto* p = rgb.data() + (size_t(y+m.origin_y)*width+x+m.origin_x)*3;
+                    if (!p[0]) p[0]=p[1]=p[2]=id;
+                    else if (p[0]==p[1] && p[1]==p[2]) p[1]=id;
+                    else if (p[0]==p[2]) p[2]=id;
+                    else return finish(YOLO_STATUS_UNSUPPORTED, "More than three masks overlap at one pixel");
+                }
+            }
+        }
+        for (int32_t y=0; y<height; ++y)
+            std::memcpy(output+size_t(y)*stride, rgb.data()+size_t(y)*width*3, size_t(width)*3);
+        return finish(YOLO_STATUS_OK, "");
+    } catch (const std::exception&) {
+        return finish(YOLO_STATUS_BACKEND_FAILED, "Cannot allocate RGB mask canvas");
+    }
+}
diff --git a/YoloRuntime/src/yolo_robust_circle.h b/YoloRuntime/src/yolo_robust_circle.h
new file mode 100644
index 0000000..7a2e3da
--- /dev/null
+++ b/YoloRuntime/src/yolo_robust_circle.h
@@ -0,0 +1,174 @@
+#pragma once
+
+// 【学习入口：根据分割 mask 的外轮廓拟合圆】
+// 输入不是灰度图，而是一圈按边界顺序排列的轮廓点；输出为圆心、半径和质量标志。
+// 计算流程：最小外接圆备用 -> 退化检查 -> 按弧长均匀采样 -> 初始圆 -> Tukey IRLS -> 质量门限。
+// “最小外接圆”要求包住所有轮廓点；“拟合圆”追求大多数边界点到圆周的距离小。
+// 所以少量突出点会推大外接圆，本算法通过降低异常点权重来抑制其对拟合的影响。
+// Shared Runtime reports fitted=false as an explicit minimum-enclosing fallback.
+
+#include <opencv2/imgproc.hpp>
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <vector>
+
+namespace yolo_robust_circle {
+
+struct Circle
+{
+    // center.x/center.y 与 radius 的单位都是原图像素；double 保留亚像素精度。
+    cv::Point2d center;
+    double radius = 0.0;
+    bool fitted = false;
+};
+
+// 几何辅助函数：求非空数组的中位数，按值接收以免重排调用方的数据。
+// nth_element 只把中间元素放到正确位置，无需对整个数组完整排序。
+// 偶数长度时，右中位数为 *middle，左中位数为左半区最大值，二者取平均。
+// 这里统计的是点到圆心的距离/拟合残差，不是像素灰度的中位数。
+inline double Median(std::vector<double> values)
+{
+    const auto middle = values.begin() + values.size() / 2;
+    std::nth_element(values.begin(), middle, values.end());
+    const double upper = *middle;
+    return values.size() % 2 ? upper
+        : (upper + *std::max_element(values.begin(), middle)) * 0.5;
+}
+
+// Uniform arc-length sampling prevents CHAIN_APPROX_SIMPLE vertices from
+// overweighting pixel staircases and underweighting long straight sections.
+inline std::vector<cv::Point2d> SampleBoundary(const std::vector<cv::Point>& contour)
+{
+    // 闭合轮廓的第 i 段连接 contour[i] 与下一点，最后一段回到第 0 点。
+    // lengths[i] 表示到第 i 个顶点的累计弧长，lengths.back() 为总周长。
+    std::vector<double> lengths(contour.size() + 1, 0.0);
+    for (size_t i = 0; i < contour.size(); ++i)
+        lengths[i + 1] = lengths[i] + cv::norm(contour[(i + 1) % contour.size()] - contour[i]);
+    if (lengths.back() <= 0.0) return {};
+    constexpr int count = 128;
+    // 固定采样 128 点，让每段边界按长度贡献，而不是按原始轮廓顶点密度贡献。
+    // 该数值是当前实现的固定参数，不代表相机分辨率或目标数量。
+    std::vector<cv::Point2d> points;
+    points.reserve(count);
+    size_t edge = 0;
+    for (int i = 0; i < count; ++i) {
+        const double distance = lengths.back() * i / count;
+        // 沿周长依次定位采样点在哪条线段上。edge 只向前走，无需每次重新搜索全部线段。
+        while (edge + 1 < contour.size() && lengths[edge + 1] <= distance) ++edge;
+        const double span = lengths[edge + 1] - lengths[edge];
+        const double t = span > 0.0 ? (distance - lengths[edge]) / span : 0.0;
+        // 线性插值 P=A+t(B-A)，得到亚像素坐标；span=0 时避免除零。
+        const cv::Point2d a = contour[edge], b = contour[(edge + 1) % contour.size()];
+        points.push_back(a + (b - a) * t);
+    }
+    return points;
+}
+
+// Fit the boundary, not a prescribed radius reduction. Tukey IRLS suppresses
+// minority protrusions. Noncircular/degenerate inputs retain the enclosing
+// circle rather than inventing a confident measurement of an arbitrary shape.
+inline Circle Fit(const std::vector<cv::Point>& contour)
+{
+    // 1. 准备失败回退。所有后续门限失败都返回 fallback，其 fitted 保持默认 false。
+    Circle fallback;
+    if (contour.empty()) return fallback;
+    cv::Point2f enclosingCenter;
+    float enclosingRadius = 0.0f;
+    cv::minEnclosingCircle(contour, enclosingCenter, enclosingRadius);
+    fallback.center = enclosingCenter;
+    fallback.radius = enclosingRadius;
+    // 轮廓点太少或面积不足时，圆参数不够稳定；面积单位为像素平方。
+    const double area = std::abs(cv::contourArea(contour));
+    if (contour.size() < 5 || area < 16.0) return fallback;
+    const auto bounds = cv::minAreaRect(contour);
+    // minAreaRect 是可旋转的最小面积矩形，不是这里最终要拟合的圆。
+    // 长短边比超过 1.5 时按明显狭长轮廓拒绝；这是粗筛，不是椭圆拟合。
+    const double longSide = std::max(bounds.size.width, bounds.size.height);
+    const double shortSide = std::min(bounds.size.width, bounds.size.height);
+    if (shortSide <= 0.0 || longSide > 1.5 * shortSide) return fallback;
+    const auto points = SampleBoundary(contour);
+    if (points.empty()) return fallback;
+    const auto moments = cv::moments(contour);
+    // 2. 用轮廓面积矩初始化圆心：cx=m10/m00，cy=m01/m00。
+    // 半径初值取 128 个采样点到这个圆心的距离中位数，以减弱少数突出点的影响。
+    if (std::abs(moments.m00) < 1e-9) return fallback;
+    cv::Point2d center(moments.m10 / moments.m00, moments.m01 / moments.m00);
+    std::vector<double> distances;
+    for (const auto& point : points) distances.push_back(cv::norm(point - center));
+    double radius = Median(distances);
+    for (int iteration = 0; iteration < 30; ++iteration) {
+        // 3. IRLS（迭代重加权最小二乘）：每轮重新计算残差与权重，再求圆参数的小修正。
+        // 参数 theta=(cx,cy,R)，第 i 点残差 e_i=||P_i-C||-R；正值在圆外，负值在圆内。
+        std::vector<double> residuals;
+        for (const auto& point : points) residuals.push_back(cv::norm(point - center) - radius);
+        const double median = Median(residuals);
+        std::vector<double> deviations;
+        for (double residual : residuals) deviations.push_back(std::abs(residual - median));
+        // MAD=median(|e_i-median(e)|) 估计残差尺度；1.4826 为尺度换算因子。
+        // cutoff 由该尺度和 Tukey 系数 4.685 得到，并设置 0.75 像素下限，避免尺度过小。
+        // 下方 u 使用 e_i/cutoff（未减去 median）；median 在这里用于估计尺度。
+        const double cutoff = std::max(0.75, 4.685 * 1.4826 * Median(deviations));
+        cv::Matx33d normal = cv::Matx33d::zeros();
+        cv::Vec3d gradient(0, 0, 0);
+        int contributors = 0;
+        for (size_t i = 0; i < points.size(); ++i) {
+            const cv::Point2d delta = center - points[i];
+            const double distance = cv::norm(delta);
+            const double u = residuals[i] / cutoff;
+            // Tukey 权重：|u|>=1 的点本轮权重为 0；其余点 w=(1-u^2)^2。
+            // 残差越小，权重越接近 1；这样少数异常边界点不会主导拟合。
+            if (distance <= 1e-9 || std::abs(u) >= 1.0) continue;
+            const double weight = (1.0 - u * u) * (1.0 - u * u);
+            const cv::Vec3d jacobian(delta.x / distance, delta.y / distance, -1.0);
+            // 残差对三个参数的导数 J=[(cx-px)/d, (cy-py)/d, -1]。
+            // 累加 H=Σw*J*J^T、g=Σw*e*J，随后解 H*step=-g，求本轮参数增量。
+            normal += weight * (jacobian * jacobian.t());
+            gradient += weight * residuals[i] * jacobian;
+            ++contributors;
+        }
+        cv::Vec3d step;
+        // 至少需要 16 个参与点；用 SVD 解 3×3 方程，求解失败或出现非有限数则回退。
+        if (contributors < 16 || !cv::solve(normal, -gradient, step, cv::DECOMP_SVD)) return fallback;
+        if (!std::isfinite(step[0]) || !std::isfinite(step[1]) || !std::isfinite(step[2])) return fallback;
+        const double stepSize = cv::norm(step);
+        // 一次修正的总长度最多为当前半径的 25%，避免初值较差时一步跳得太远。
+        if (stepSize > radius * 0.25) step *= radius * 0.25 / stepSize;
+        center += cv::Point2d(step[0], step[1]);
+        radius += step[2];
+        if (!std::isfinite(radius) || radius <= 1.0) return fallback;
+        if (cv::norm(step) < 1e-5) break;
+    }
+    // Require support around the entire circle and a predominantly circular
+    // boundary. A short arc or elongated object must not masquerade as a fit.
+    std::array<bool, 12> sectors{};
+    // 4. 优化能算出一个圆，不等于轮廓确实近似圆。以下门限联合决定 fitted=true。
+    // 把方向分为 12 个扇区，仅由误差 <= max(1px,0.10R) 的点提供扇区支持。
+    // 至少 10 个扇区有支持，用于抑制“只有短弧却拟合出大圆”的情况。
+    std::vector<double> errors;
+    for (const auto& point : points) {
+        const auto delta = point - center;
+        const double error = std::abs(cv::norm(delta) - radius);
+        errors.push_back(error);
+        if (error <= std::max(1.0, radius * 0.10)) {
+            const double angle = std::atan2(delta.y, delta.x) + CV_PI;
+            // atan2 角度从 [-π,π] 平移到 [0,2π]；min(11,...) 处理末端落到索引 12 的边界。
+            const int sector = std::min(11, static_cast<int>(angle * 12.0 / (2.0 * CV_PI)));
+            sectors[sector] = true;
+        }
+    }
+    std::sort(errors.begin(), errors.end());
+    // 这里只对 128 个几何误差排序。约 80% 分位误差要求 <= max(1px,0.10R)，
+    // 同时要求：轮廓面积/圆面积在 [0.65,1.35]、圆心位于轮廓内或边上、
+    // 拟合半径不超过备用外接圆半径的 1.10 倍。任一失败都返回 fitted=false。
+    // 面积使用输入的外轮廓面积；内部孔洞不参与这项外形检查。
+    const double areaRatio = area / (CV_PI * radius * radius);
+    if (errors[static_cast<size_t>(0.8 * (errors.size() - 1))] > std::max(1.0, radius * 0.10)
+        || std::count(sectors.begin(), sectors.end(), true) < 10
+        || areaRatio < 0.65 || areaRatio > 1.35
+        || cv::pointPolygonTest(contour, center, false) < 0.0
+        || radius > fallback.radius * 1.10) return fallback;
+    return {center, radius, true};
+}
+
+} // namespace yolo_robust_circle
diff --git a/YoloRuntime/src/yolo_runtime.cpp b/YoloRuntime/src/yolo_runtime.cpp
index fd1b153..8730781 100644
--- a/YoloRuntime/src/yolo_runtime.cpp
+++ b/YoloRuntime/src/yolo_runtime.cpp
@@ -158,7 +158,8 @@ static std::unique_ptr<yolo_result_set> copy_public_results(
                     item.mask_data + static_cast<size_t>(row) * item.mask_stride_bytes,
                     static_cast<size_t>(item.mask_width));
             }
-            const auto boundary = yolo_seg_geometry::mask_boundary(
+            const auto boundary = geometry_mode == YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE
+                ? std::vector<yolo_seg_geometry::Point>{} : yolo_seg_geometry::mask_boundary(
                 result.mask.data(),
                 result.mask_width,
                 result.mask_height,
@@ -168,12 +169,20 @@ static std::unique_ptr<yolo_result_set> copy_public_results(
             result.seg_geometry.struct_size = sizeof(result.seg_geometry);
             result.seg_geometry.version = YOLO_SEG_GEOMETRY_VERSION;
             result.seg_geometry.type = geometry_mode;
-            if (geometry_mode == YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE) {
-                const auto circle = yolo_seg_geometry::minimum_enclosing_circle(boundary);
-                if (!circle.valid) throw std::runtime_error("cannot calculate Seg minimum enclosing circle");
+            if (geometry_mode != YOLO_SEG_GEOMETRY_MIN_AREA_RECT) {
+                const auto circle = geometry_mode == YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE
+                    ? yolo_seg_geometry::robust_fit_circle(result.mask.data(), result.mask_width,
+                        result.mask_height, result.mask_stride_bytes, result.mask_origin_x, result.mask_origin_y)
+                    : (geometry_mode == YOLO_SEG_GEOMETRY_MEAN_DIAMETER_CIRCLE
+                        ? yolo_seg_geometry::mean_diameter_circle(boundary)
+                        : yolo_seg_geometry::minimum_enclosing_circle(boundary));
+                if (!circle.valid) throw std::runtime_error("cannot calculate Seg circle");
                 result.seg_geometry.center_x = static_cast<float>(circle.center_x);
                 result.seg_geometry.center_y = static_cast<float>(circle.center_y);
                 result.seg_geometry.radius = static_cast<float>(circle.radius);
+                if (geometry_mode == YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE)
+                    result.seg_geometry.fit_status = circle.fitted
+                        ? YOLO_SEG_FIT_SUCCEEDED : YOLO_SEG_FIT_ENCLOSING_FALLBACK;
             } else {
                 const auto rectangle = yolo_seg_geometry::minimum_area_rect(boundary);
                 if (!rectangle.valid) throw std::runtime_error("cannot calculate Seg minimum-area rectangle");
@@ -765,10 +774,14 @@ extern "C" yolo_status_t yolo_runtime_get_info(
     info->capabilities = YOLO_CAPABILITY_INFER_IMAGE;
     if (runtime->task == YOLO_TASK_SEG) {
         info->capabilities |= YOLO_CAPABILITY_SEG_MIN_AREA_RECT |
-                              YOLO_CAPABILITY_SEG_MIN_ENCLOSING_CIRCLE;
+                              YOLO_CAPABILITY_SEG_MIN_ENCLOSING_CIRCLE |
+                              YOLO_CAPABILITY_SEG_MEAN_DIAMETER_CIRCLE |
+                              YOLO_CAPABILITY_SEG_ROBUST_FIT_CIRCLE;
         info->supported_seg_geometry_modes =
             YOLO_SEG_GEOMETRY_BIT(YOLO_SEG_GEOMETRY_MIN_AREA_RECT) |
-            YOLO_SEG_GEOMETRY_BIT(YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE);
+            YOLO_SEG_GEOMETRY_BIT(YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE) |
+            YOLO_SEG_GEOMETRY_BIT(YOLO_SEG_GEOMETRY_MEAN_DIAMETER_CIRCLE) |
+            YOLO_SEG_GEOMETRY_BIT(YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE);
     }
     info->supported_pixel_formats =
         YOLO_PIXEL_FORMAT_BIT(YOLO_PIXEL_FORMAT_GRAY8) |
@@ -803,8 +816,10 @@ extern "C" yolo_status_t yolo_runtime_infer_image(
     }
     if (runtime->task == YOLO_TASK_SEG) {
         if (options->seg_geometry_mode != YOLO_SEG_GEOMETRY_MIN_AREA_RECT &&
-            options->seg_geometry_mode != YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE) {
-            set_error(error, YOLO_STATUS_INVALID_ARGUMENT, "Seg requires minimum-area rectangle or minimum enclosing circle");
+            options->seg_geometry_mode != YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE &&
+            options->seg_geometry_mode != YOLO_SEG_GEOMETRY_MEAN_DIAMETER_CIRCLE &&
+            options->seg_geometry_mode != YOLO_SEG_GEOMETRY_ROBUST_FIT_CIRCLE) {
+            set_error(error, YOLO_STATUS_INVALID_ARGUMENT, "Seg requires rectangle, enclosing circle, mean circle or robust fit circle");
             return YOLO_STATUS_INVALID_ARGUMENT;
         }
     } else if (options->seg_geometry_mode != YOLO_SEG_GEOMETRY_NONE) {
diff --git a/YoloRuntime/src/yolo_seg_geometry.cpp b/YoloRuntime/src/yolo_seg_geometry.cpp
index 3f93df5..3a660d2 100644
--- a/YoloRuntime/src/yolo_seg_geometry.cpp
+++ b/YoloRuntime/src/yolo_seg_geometry.cpp
@@ -1,4 +1,5 @@
 #include "yolo_seg_geometry.h"
+#include "yolo_robust_circle.h"
 
 #include <algorithm>
 #include <cmath>
@@ -201,4 +202,24 @@ RotatedRect minimum_area_rect(const std::vector<Point>& input) {
     return best;
 }
 
+Circle mean_diameter_circle(const std::vector<Point>& points) {
+    const auto rect = minimum_area_rect(points);
+    return {rect.center_x, rect.center_y, (rect.width + rect.height) * 0.25, rect.valid};
+}
+
+Circle robust_fit_circle(const unsigned char* mask, int width, int height,
+                         int stride, int origin_x, int origin_y) {
+    if (!mask || width <= 0 || height <= 0 || stride < width) return {};
+    cv::Mat view(height, width, CV_8U, const_cast<unsigned char*>(mask), stride);
+    std::vector<std::vector<cv::Point>> contours;
+    cv::findContours(view.clone(), contours, cv::RETR_EXTERNAL, cv::CHAIN_APPROX_SIMPLE);
+    if (contours.empty()) return {};
+    auto best = std::max_element(contours.begin(), contours.end(), [](const auto& a, const auto& b) {
+        return cv::contourArea(a) < cv::contourArea(b);
+    });
+    for (auto& point : *best) point += cv::Point(origin_x, origin_y);
+    const auto circle = yolo_robust_circle::Fit(*best);
+    return {circle.center.x, circle.center.y, circle.radius, true, circle.fitted};
+}
+
 } // namespace yolo_seg_geometry
diff --git a/YoloRuntime/src/yolo_seg_geometry.h b/YoloRuntime/src/yolo_seg_geometry.h
index 693f6a4..46d020d 100644
--- a/YoloRuntime/src/yolo_seg_geometry.h
+++ b/YoloRuntime/src/yolo_seg_geometry.h
@@ -14,6 +14,7 @@ struct Circle {
     double center_y = 0.0;
     double radius = 0.0;
     bool valid = false;
+    bool fitted = false;
 };
 
 struct RotatedRect {
@@ -35,5 +36,9 @@ std::vector<Point> mask_boundary(
 
 Circle minimum_enclosing_circle(const std::vector<Point>& points);
 RotatedRect minimum_area_rect(const std::vector<Point>& points);
+Circle mean_diameter_circle(const std::vector<Point>& points);
+// Largest external contour; returns its enclosing circle when robust fitting fails.
+Circle robust_fit_circle(const unsigned char* mask, int width, int height,
+                         int stride, int origin_x, int origin_y);
 
 } // namespace yolo_seg_geometry
diff --git a/YoloRuntime/tests/c_api_contract.c b/YoloRuntime/tests/c_api_contract.c
index 9c66a1b..4011e5f 100644
--- a/YoloRuntime/tests/c_api_contract.c
+++ b/YoloRuntime/tests/c_api_contract.c
@@ -23,6 +23,11 @@ _Static_assert(YOLO_RUNTIME_ABI_VERSION == 5u, "Runtime ABI version changed");
 _Static_assert(YOLO_IMAGE_VIEW_ABI_VERSION == 1u, "Image view version changed");
 _Static_assert(YOLO_INFER_OPTIONS_VERSION == 1u, "Infer-options version changed");
 _Static_assert(YOLO_LABEL_LENGTH == 64u, "Label length changed");
+_Static_assert(YOLO_SEG_GEOMETRY_MIN_AREA_RECT == 1, "Rectangle mode changed");
+_Static_assert(YOLO_SEG_GEOMETRY_MIN_ENCLOSING_CIRCLE == 2, "Enclosing mode changed");
+_Static_assert(sizeof(yolo_seg_geometry_v1_t) == 68, "Geometry ABI 5 size changed");
+_Static_assert(offsetof(yolo_seg_geometry_v1_t, radius) == 32, "Radius ABI offset changed");
+_Static_assert(offsetof(yolo_seg_geometry_v1_t, fit_status) == 36, "Fit status must use reserved word");
 
 _Static_assert(YOLO_STATUS_OK == 0, "OK status changed");
 _Static_assert(YOLO_STATUS_INVALID_ARGUMENT == -1, "Invalid-argument status changed");
@@ -51,6 +56,9 @@ ASSERT_FIELD_ORDER(yolo_mask_view_v1_t, data, width);
 ASSERT_FIELD_ORDER(yolo_mask_view_v1_t, row_stride_bytes, origin_x);
 
 int main(void) {
+    unsigned char rgb_ids[3] = {1, 2, 3};
+    if (yolo_masks_compose_rgb_ids(NULL, 0, 1, 1, rgb_ids, 3, sizeof(rgb_ids), NULL) != YOLO_STATUS_OK ||
+        rgb_ids[0] || rgb_ids[1] || rgb_ids[2]) return 2;
     yolo_image_view_v1_t image = {0};
     yolo_infer_options_v1_t options = {0};
     yolo_error_info_v1_t error = {0};
diff --git a/YoloRuntime/tests/mask_ids_test.cpp b/YoloRuntime/tests/mask_ids_test.cpp
new file mode 100644
index 0000000..861b577
--- /dev/null
+++ b/YoloRuntime/tests/mask_ids_test.cpp
@@ -0,0 +1,74 @@
+#include "yolo_runtime.h"
+#include <array>
+#include <cassert>
+#include <cstdio>
+#include <set>
+#include <vector>
+
+static yolo_mask_view_v1_t view(const unsigned char* data, int w, int h, int stride, int x=0, int y=0) {
+    yolo_mask_view_v1_t m{};
+    m.struct_size=sizeof(m); m.version=YOLO_MASK_VIEW_VERSION;
+    m.data=data; m.width=w; m.height=h; m.row_stride_bytes=stride; m.origin_x=x; m.origin_y=y;
+    return m;
+}
+int main() {
+    // Input padding contains nonbinary sentinels; holes and disconnected pixels remain intact.
+    const unsigned char a[]={255,0,255,99, 0,255,0,99, 255,0,255,99};
+    const unsigned char b[]={255,255,0,99, 0,255,0,99, 255,0,0,99};
+    const unsigned char c[]={255,0,0,99, 0,255,0,99, 0,0,255,99};
+    std::vector<yolo_mask_view_v1_t> masks={view(a,3,3,4,1,1),view(b,3,3,4,1,1),view(c,3,3,4,1,1)};
+    const int w=5,h=5,stride=17;
+    std::vector<unsigned char> rgb(stride*h,77);
+    yolo_error_info_v1_t error{};error.struct_size=sizeof(error);error.version=YOLO_ERROR_INFO_VERSION;
+    const auto compose=[&](uint32_t n) {
+        return yolo_masks_compose_rgb_ids(masks.data(),n,w,h,rgb.data(),stride,rgb.size(),&error);
+    };
+    // Independently reconstruct each membership from the channels and compare every input pixel.
+    for(uint32_t n=1;n<=3;++n) {
+        assert(compose(n)==YOLO_STATUS_OK);
+        for(int y=0;y<h;++y) for(int x=0;x<w;++x) {
+            std::set<int> expected,actual;
+            for(uint32_t i=0;i<n;++i) {
+                const auto& m=masks[i];
+                if(x>=m.origin_x && x<m.origin_x+m.width && y>=m.origin_y && y<m.origin_y+m.height &&
+                   m.data[(y-m.origin_y)*m.row_stride_bytes+x-m.origin_x]) expected.insert(i+1);
+            }
+            const auto* p=&rgb[y*stride+x*3];
+            for(int k=0;k<3;++k) if(p[k]) actual.insert(p[k]);
+            assert(actual==expected);
+            if(expected.empty()) assert(p[0]==0 && p[1]==0 && p[2]==0);
+            else if(expected.size()==1) assert(p[0]==*expected.begin() && p[0]==p[1] && p[1]==p[2]);
+            else if(expected.size()==2) assert(p[0]==*expected.begin() && p[1]==*expected.rbegin() && p[2]==p[0]);
+            else assert(p[0]==1 && p[1]==2 && p[2]==3);
+        }
+        for(int y=0;y<h;++y) assert(rgb[y*stride+15]==77 && rgb[y*stride+16]==77);
+    }
+    // Every error must preserve all caller bytes, including partial-overlap overflow.
+    masks.push_back(masks[0]);
+    const auto saved=rgb;
+    assert(compose(4)==YOLO_STATUS_UNSUPPORTED && error.message[0]); assert(rgb==saved);
+    masks[0].origin_x=4;
+    assert(compose(1)==YOLO_STATUS_INVALID_ARGUMENT); assert(rgb==saved);
+    masks[0].origin_x=1; masks[0].row_stride_bytes=2;
+    assert(compose(1)==YOLO_STATUS_INVALID_ARGUMENT); assert(rgb==saved);
+    masks[0].row_stride_bytes=4; masks[0].version=0;
+    assert(compose(1)==YOLO_STATUS_ABI_MISMATCH); assert(rgb==saved);
+    masks[0]=view(a,3,3,4,1,1);
+    assert(yolo_masks_compose_rgb_ids(masks.data(),1,w,h,rgb.data(),stride,1,&error)==YOLO_STATUS_BUFFER_TOO_SMALL);
+    assert(rgb==saved);
+    const unsigned char bad[]={255,1};masks[0]=view(bad,2,1,2);
+    assert(compose(1)==YOLO_STATUS_INVALID_ARGUMENT); assert(rgb==saved);
+    assert(yolo_masks_compose_rgb_ids(nullptr,1,w,h,rgb.data(),stride,rgb.size(),nullptr)==YOLO_STATUS_INVALID_ARGUMENT);
+    assert(yolo_masks_compose_rgb_ids(nullptr,256,w,h,rgb.data(),stride,rgb.size(),nullptr)==YOLO_STATUS_UNSUPPORTED);
+    assert(rgb==saved);
+    assert(yolo_masks_compose_rgb_ids(nullptr,0,w,h,rgb.data(),stride,rgb.size(),nullptr)==YOLO_STATUS_OK);
+    for(int y=0;y<h;++y) for(int x=0;x<w*3;++x) assert(rgb[y*stride+x]==0);
+    // Full byte ID range, without assigning IDs from semantic class IDs.
+    const unsigned char foreground=255;
+    masks.clear();
+    for(int i=0;i<255;++i) masks.push_back(view(&foreground,1,1,1,i,0));
+    rgb.assign(255*3,0);
+    assert(yolo_masks_compose_rgb_ids(masks.data(),255,255,1,rgb.data(),765,rgb.size(),nullptr)==YOLO_STATUS_OK);
+    for(int i=0;i<255;++i) for(int k=0;k<3;++k) assert(rgb[i*3+k]==i+1);
+    std::puts("RGB_ID_MASK_OK: exact encoding, independent decode, offsets/strides/holes, 255 IDs, atomic errors");
+}
diff --git a/YoloRuntime/tests/runner_mask_output_test.cpp b/YoloRuntime/tests/runner_mask_output_test.cpp
new file mode 100644
index 0000000..a9572ea
--- /dev/null
+++ b/YoloRuntime/tests/runner_mask_output_test.cpp
@@ -0,0 +1,26 @@
+#include "runner_mask_output.h"
+#include <cassert>
+#include <vector>
+#include <sstream>
+#include <iterator>
+
+int main() {
+    unsigned char data[]={255,0,99, 0,255,99}; // Padded rows; preserve holes.
+    yolo_mask_view_v1_t mask{};mask.data=data;mask.width=mask.height=2;
+    mask.row_stride_bytes=3;mask.origin_x=1;mask.origin_y=1;
+    std::vector<unsigned char> image(4*4*4,100);
+    assert(runner_mask_output::blend(image.data(),4,4,16,4,mask,0));
+    assert(image[20]==61 && image[21]==147 && image[22]==108 && image[23]==100);
+    assert(image[24]==100 && image[36]==100 && image[40]!=100);
+    auto invalid=mask;invalid.origin_x=4;
+    assert(!runner_mask_output::blend(image.data(),4,4,16,4,invalid,0));
+    const auto path=std::filesystem::temp_directory_path()/"yolo-instance-mask-contract.pgm";
+    assert(runner_mask_output::save(path,mask));
+    std::ifstream file(path,std::ios::binary);
+    std::vector<unsigned char> bytes((std::istreambuf_iterator<char>(file)),{});
+    const std::string header="P5\n2 2\n255\n";
+    assert(bytes.size()==header.size()+4);
+    assert(std::equal(header.begin(),header.end(),bytes.begin()));
+    assert(bytes[header.size()]==255 && bytes[header.size()+1]==0 && bytes.back()==255);
+    file.close();std::filesystem::remove(path);
+}
diff --git a/YoloRuntime/tests/seg_geometry_test.cpp b/YoloRuntime/tests/seg_geometry_test.cpp
index 1f5323f..4ce4224 100644
--- a/YoloRuntime/tests/seg_geometry_test.cpp
+++ b/YoloRuntime/tests/seg_geometry_test.cpp
@@ -1,4 +1,5 @@
 #include "yolo_seg_geometry.h"
+#include <opencv2/imgproc.hpp>
 
 #include <cassert>
 #include <cmath>
@@ -35,6 +36,37 @@ int main() {
     assert(close_to(circle.center_x, 12.5));
     assert(close_to(circle.center_y, 22.0));
     assert(close_to(circle.radius, std::sqrt(13.0) * 0.5));
+    const auto mean = yolo_seg_geometry::mean_diameter_circle(boundary);
+    assert(mean.valid && !mean.fitted);
+    assert(close_to(mean.center_x, rect.center_x));
+    assert(close_to(mean.center_y, rect.center_y));
+    assert(close_to(mean.radius, 1.25)); // Not half the short side, nor enclosing radius.
+
+    cv::Mat disk = cv::Mat::zeros(121, 121, CV_8U);
+    cv::circle(disk, {60, 60}, 30, cv::Scalar(255), -1);
+    auto fit = yolo_seg_geometry::robust_fit_circle(disk.data, disk.cols, disk.rows, int(disk.step), 10, 20);
+    assert(fit.valid && fit.fitted);
+    assert(close_to(fit.center_x, 70, .1) && close_to(fit.center_y, 80, .1));
+    assert(close_to(fit.radius, 30, 1));
+    // Disconnected noise must not replace or enlarge the largest-contour fit.
+    disk.at<unsigned char>(2, 2) = 255;
+    const auto noisy = yolo_seg_geometry::robust_fit_circle(disk.data, disk.cols, disk.rows, int(disk.step), 10, 20);
+    assert(noisy.fitted && close_to(noisy.radius, fit.radius));
+    cv::line(disk, {87, 60}, {103, 60}, cv::Scalar(255), 2);
+    const auto spiked = yolo_seg_geometry::robust_fit_circle(disk.data, disk.cols, disk.rows, int(disk.step), 0, 0);
+    assert(spiked.valid && spiked.fitted && close_to(spiked.radius, 30, 1));
+    cv::Mat elongated = cv::Mat::zeros(50, 100, CV_8U);
+    cv::rectangle(elongated, {10, 10}, {80, 20}, cv::Scalar(255), -1);
+    const auto fallback = yolo_seg_geometry::robust_fit_circle(elongated.data, elongated.cols, elongated.rows, int(elongated.step), 0, 0);
+    assert(fallback.valid && !fallback.fitted);
+    assert(close_to(fallback.radius, std::sqrt(70.*70.+10.*10.)*.5, .001));
+    const unsigned char point[] = {255};
+    const auto single = yolo_seg_geometry::robust_fit_circle(point, 1, 1, 1, 5, 8);
+    assert(single.valid && !single.fitted && close_to(single.center_x, 5) && close_to(single.center_y, 8));
+    assert(!yolo_seg_geometry::robust_fit_circle(nullptr, 1, 1, 1, 0, 0).valid);
+    const unsigned char empty[] = {0};
+    assert(!yolo_seg_geometry::robust_fit_circle(empty, 1, 1, 1, 0, 0).valid);
+    assert(!yolo_seg_geometry::mean_diameter_circle({}).valid);
 
     const std::vector<yolo_seg_geometry::Point> rotated_square = {
         {0.0, -2.0}, {2.0, 0.0}, {0.0, 2.0}, {-2.0, 0.0}};
diff --git a/YoloRuntime/tests/verify_four_geometry.py b/YoloRuntime/tests/verify_four_geometry.py
new file mode 100644
index 0000000..8140e5b
--- /dev/null
+++ b/YoloRuntime/tests/verify_four_geometry.py
@@ -0,0 +1,144 @@
+"""Public C API real-sample regression against a saved geometry comparison run."""
+import argparse
+import ctypes as C
+import hashlib
+import json
+import os
+from pathlib import Path
+
+import cv2
+import numpy as np
+
+class Image(C.Structure):
+    _fields_ = [('struct_size', C.c_uint32), ('version', C.c_uint32), ('data', C.c_void_p),
+                ('width', C.c_int32), ('height', C.c_int32), ('stride', C.c_int32),
+                ('format', C.c_int32), ('reserved', C.c_uint32 * 8)]
+
+class Options(C.Structure):
+    _fields_ = [('struct_size', C.c_uint32), ('version', C.c_uint32), ('mode', C.c_int32), ('reserved', C.c_uint32 * 13)]
+
+class Error(C.Structure):
+    _fields_ = [('struct_size', C.c_uint32), ('version', C.c_uint32), ('status', C.c_int32), ('message', C.c_char * 512), ('reserved', C.c_uint32 * 8)]
+
+class Info(C.Structure):
+    _fields_ = [('struct_size', C.c_uint32), ('version', C.c_uint32)] + [(n, C.c_uint32) for n in
+        ['abi', 'task', 'capabilities', 'formats', 'modes', 'max_results', 'max_keypoints']] + [('reserved', C.c_uint32 * 8)]
+
+class Geometry(C.Structure):
+    _fields_ = [('struct_size', C.c_uint32), ('version', C.c_uint32), ('type', C.c_int32)] + [(n, C.c_float) for n in
+        ['x', 'y', 'width', 'height', 'angle', 'radius']] + [('fit_status', C.c_uint32), ('reserved', C.c_uint32 * 7)]
+
+class Mask(C.Structure):
+    _fields_ = [('struct_size', C.c_uint32), ('version', C.c_uint32), ('data', C.c_void_p)] + [(n, C.c_int32) for n in
+        ['width', 'height', 'stride', 'x', 'y']] + [('reserved', C.c_uint32 * 8)]
+
+def versioned(cls):
+    value = cls(); value.struct_size = C.sizeof(cls); value.version = 1
+    return value
+
+def main():
+    p = argparse.ArgumentParser()
+    p.add_argument('--install', type=Path, required=True)
+    p.add_argument('--evidence', type=Path, required=True)
+    p.add_argument('--reference', type=Path, action='append', required=True,
+                   help='Prior run directory containing raw.json and provenance.json; tests its first image')
+    args = p.parse_args(); args.evidence.mkdir(parents=True, exist_ok=True)
+    libdir = args.install.resolve() / 'lib'
+    cookie = os.add_dll_directory(str(libdir)) if os.name == 'nt' else None
+    lib = C.CDLL(str(libdir / ('yolo_runtime.dll' if os.name == 'nt' else 'libyolo_runtime.so')))
+    signatures = {
+        'yolo_runtime_create': ([C.c_char_p, C.POINTER(C.c_void_p), C.POINTER(Error)], C.c_int32),
+        'yolo_runtime_get_info': ([C.c_void_p, C.POINTER(Info)], C.c_int32),
+        'yolo_runtime_infer_image': ([C.c_void_p, C.POINTER(Image), C.POINTER(Options), C.POINTER(C.c_void_p), C.POINTER(Error)], C.c_int32),
+        'yolo_result_set_get_count': ([C.c_void_p, C.POINTER(C.c_uint32)], C.c_int32),
+        'yolo_result_set_get_seg_geometry': ([C.c_void_p, C.c_uint32, C.POINTER(Geometry)], C.c_int32),
+        'yolo_result_set_get_seg_mask': ([C.c_void_p, C.c_uint32, C.POINTER(Mask)], C.c_int32),
+        'yolo_result_set_release': ([C.c_void_p], None), 'yolo_runtime_destroy': ([C.c_void_p], None)}
+    for name, (types, result) in signatures.items():
+        f = getattr(lib, name); f.argtypes = types; f.restype = result
+    assert C.sizeof(Geometry) == 68 and Geometry.radius.offset == 32 and Geometry.fit_status.offset == 36
+    reports = []
+    for ri, reference in enumerate(args.reference):
+        provenance = json.loads((reference / 'provenance.json').read_text(encoding='utf-8'))
+        raw = json.loads((reference / 'raw.json').read_text(encoding='utf-8'))
+        first = raw['images'][0]
+        model = Path(provenance['model']); image_path = Path(provenance['input']) / first['image']
+        assert hashlib.sha256(model.read_bytes()).hexdigest() == provenance['model_sha256']
+        # Labels do not affect segmentation geometry; preserve the actual model metadata.
+        import onnx
+        import ast
+        metadata = {v.key: v.value for v in onnx.load(str(model), load_external_data=False).metadata_props}
+        labels = list(ast.literal_eval(metadata['names']).values())
+        config = args.evidence / f'config-{ri}.yaml'
+        config.write_text(f'''schema_version: 1
+name: four_geometry_test
+version: 1
+task: seg
+model: {json.dumps(str(model), ensure_ascii=False)}
+target_platform: rk3588
+model_family: yolo8
+output_contract: task_specific
+input:
+  width: {raw['imgsz']}
+  height: {raw['imgsz']}
+  format: rgb
+  layout: nchw
+  normalization:
+    mean: [0, 0, 0]
+    std: [255, 255, 255]
+postprocess:
+  adapter: ultralytics_yolo8_seg
+  confidence_threshold: {raw['conf']}
+  nms_threshold: {raw['iou']}
+  class_agnostic_nms: false
+labels: {json.dumps(labels)}
+''', encoding='utf-8')
+        runtime = C.c_void_p(); error = versioned(Error)
+        assert lib.yolo_runtime_create(str(config.resolve()).encode('utf-8'), C.byref(runtime), C.byref(error)) == 0, bytes(error.message)
+        try:
+            info = versioned(Info); assert lib.yolo_runtime_get_info(runtime, C.byref(info)) == 0
+            assert info.abi == 5 and info.modes == 30 and info.capabilities & 30 == 30
+            image = cv2.imdecode(np.fromfile(str(image_path), np.uint8), cv2.IMREAD_COLOR)
+            image = np.ascontiguousarray(image)
+            view = versioned(Image); view.data = image.ctypes.data; view.width = image.shape[1]; view.height = image.shape[0]
+            view.stride = image.strides[0]; view.format = 2
+            maxima = {mode: 0.0 for mode in range(1, 5)}
+            for mode in [1, 2, 3, 4, 0, 5]:
+                options = versioned(Options); options.mode = mode; results = C.c_void_p()
+                status = lib.yolo_runtime_infer_image(runtime, C.byref(view), C.byref(options), C.byref(results), C.byref(error))
+                if mode in (0, 5):
+                    assert status == -1 and not results.value
+                    continue
+                assert status == 0, bytes(error.message)
+                try:
+                    count = C.c_uint32(); assert lib.yolo_result_set_get_count(results, C.byref(count)) == 0
+                    assert count.value == len(first['targets'])
+                    for i, expected in enumerate(first['targets']):
+                        g = versioned(Geometry); m = versioned(Mask)
+                        assert lib.yolo_result_set_get_seg_geometry(results, i, C.byref(g)) == 0
+                        assert lib.yolo_result_set_get_seg_mask(results, i, C.byref(m)) == 0
+                        expected_status = (1 if expected['fitted'] else 2) if mode == 4 else 0
+                        assert g.type == mode and g.fit_status == expected_status
+                        local = np.ctypeslib.as_array((C.c_uint8 * (m.stride*m.height)).from_address(m.data)).reshape(m.height, m.stride)[:, :m.width]
+                        full = np.zeros(image.shape[:2], np.uint8); full[m.y:m.y+m.height, m.x:m.x+m.width] = local
+                        assert hashlib.sha256(full.tobytes()).hexdigest() == expected['mask_sha256']
+                        if mode == 4: want = [expected['fit_x'], expected['fit_y'], expected['fit_r']]; got = [g.x, g.y, g.radius]
+                        elif mode == 3: want = [expected['mean_x'], expected['mean_y'], expected['mean_r']]; got = [g.x, g.y, g.radius]
+                        elif mode == 1: want = [expected['mean_x'], expected['mean_y'], expected['rect_w'], expected['rect_h']]; got = [g.x, g.y, g.width, g.height]
+                        else:
+                            yy, xx = np.nonzero(full)
+                            center, radius = cv2.minEnclosingCircle(np.column_stack([xx, yy]).astype(np.float32))
+                            want = [*center, radius]; got = [g.x, g.y, g.radius]
+                        diff = max(abs(a-b) for a,b in zip(got,want)); assert diff < .002, (mode, i, diff)
+                        maxima[mode] = max(maxima[mode], diff)
+                finally:
+                    lib.yolo_result_set_release(results)
+            reports.append(dict(reference=str(reference), image=first['image'], targets=len(first['targets']), max_error_px=maxima,
+                                masks_unchanged=True, modes=[1,2,3,4], invalid_modes_rejected=[0,5]))
+        finally:
+            lib.yolo_runtime_destroy(runtime)
+    (args.evidence / 'four-mode-api.json').write_text(json.dumps(reports, ensure_ascii=False, indent=2), encoding='utf-8')
+    print('FOUR_GEOMETRY_PUBLIC_API_PASS', json.dumps(reports, ensure_ascii=False))
+
+if __name__ == '__main__':
+    main()
diff --git a/YoloRuntime/yolo_runtime.def b/YoloRuntime/yolo_runtime.def
index f42d750..cbce252 100644
--- a/YoloRuntime/yolo_runtime.def
+++ b/YoloRuntime/yolo_runtime.def
@@ -1,5 +1,6 @@
 LIBRARY yolo_runtime
 EXPORTS
+    yolo_masks_compose_rgb_ids
     yolo_runtime_get_abi_version
     yolo_runtime_create
     yolo_runtime_get_info