Merge pull request #18498 from firebladed:patch-1

Add V4L2_PIX_FMT_Y16_BE pixel format #18498

Address #18495
relates to #23944

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
- [ ] The PR is proposed to proper branch
- [x] There is reference to original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake
- [ ] Test using Melexis MLX90640

modules/videoio/src/cap_v4l.cpp

@@ -268,6 +268,14 @@ typedef uint32_t __u32;
 #define V4L2_PIX_FMT_Y12 v4l2_fourcc('Y', '1', '2', ' ')
 #endif
 
+#ifndef V4L2_PIX_FMT_Y16
+#define V4L2_PIX_FMT_Y16 v4l2_fourcc('Y', '1', '6', ' ')
+#endif
+
+#ifndef V4L2_PIX_FMT_Y16_BE
+#define V4L2_PIX_FMT_Y16_BE v4l2_fourcc_be('Y', '1', '6', ' ')
+#endif
+
 #ifndef V4L2_PIX_FMT_ABGR32
 #define V4L2_PIX_FMT_ABGR32  v4l2_fourcc('A', 'R', '2', '4')
 #endif
@@ -609,6 +617,7 @@ bool CvCaptureCAM_V4L::autosetup_capture_mode_v4l2()
             V4L2_PIX_FMT_JPEG,
 #endif
             V4L2_PIX_FMT_Y16,
+            V4L2_PIX_FMT_Y16_BE,
             V4L2_PIX_FMT_Y12,
             V4L2_PIX_FMT_Y10,
             V4L2_PIX_FMT_GREY,
@@ -668,6 +677,7 @@ bool CvCaptureCAM_V4L::convertableToRgb() const
     case V4L2_PIX_FMT_SGBRG8:
     case V4L2_PIX_FMT_RGB24:
     case V4L2_PIX_FMT_Y16:
+    case V4L2_PIX_FMT_Y16_BE:
     case V4L2_PIX_FMT_Y10:
     case V4L2_PIX_FMT_GREY:
     case V4L2_PIX_FMT_BGR24:
@@ -716,6 +726,7 @@ void CvCaptureCAM_V4L::v4l2_create_frame()
             size.height = size.height * 3 / 2; // "1.5" channels
             break;
         case V4L2_PIX_FMT_Y16:
+        case V4L2_PIX_FMT_Y16_BE:
         case V4L2_PIX_FMT_Y12:
         case V4L2_PIX_FMT_Y10:
             depth = IPL_DEPTH_16U;
@@ -1731,8 +1742,21 @@ void CvCaptureCAM_V4L::convertToRgb(const Buffer &currentBuffer)
         return;
     case V4L2_PIX_FMT_Y16:
     {
+        // https://www.kernel.org/doc/html/v4.10/media/uapi/v4l/pixfmt-y16.html
+        // This is a grey-scale image with a depth of 16 bits per pixel. The least significant byte is stored at lower memory addresses (little-endian).
+        // Note: 10-bits precision is not supported
         cv::Mat temp(imageSize, CV_8UC1, buffers[MAX_V4L_BUFFERS].memories[MEMORY_RGB].start);
-        cv::Mat(imageSize, CV_16UC1, start).convertTo(temp, CV_8U, 1.0 / 256);
+        cv::extractChannel(cv::Mat(imageSize, CV_8UC2, start), temp, 1);  // 1 - second channel
+        cv::cvtColor(temp, destination, COLOR_GRAY2BGR);
+        return;
+    }
+    case V4L2_PIX_FMT_Y16_BE:
+    {
+        // https://www.kernel.org/doc/html/v4.10/media/uapi/v4l/pixfmt-y16-be.html
+        // This is a grey-scale image with a depth of 16 bits per pixel. The most significant byte is stored at lower memory addresses (big-endian).
+        // Note: 10-bits precision is not supported
+        cv::Mat temp(imageSize, CV_8UC1, buffers[MAX_V4L_BUFFERS].memories[MEMORY_RGB].start);
+        cv::extractChannel(cv::Mat(imageSize, CV_8UC2, start), temp, 0);  // 0 - first channel
         cv::cvtColor(temp, destination, COLOR_GRAY2BGR);
         return;
     }

modules/videoio/test/test_precomp.hpp

@@ -60,7 +60,8 @@ inline std::string fourccToString(int fourcc)
 inline std::string fourccToStringSafe(int fourcc)
 {
     std::string res = fourccToString(fourcc);
-    std::replace_if(res.begin(), res.end(), [](uint8_t c){ return c < '0' || c > 'z'; }, '_');
+    // TODO: return hex values for invalid characters
+    std::transform(res.begin(), res.end(), res.begin(), [](uint8_t c) { return (c >= '0' && c <= 'z') ? c : (c == ' ' ? '_' : 'x'); });
     return res;
 }
 

modules/videoio/test/test_v4l2.cpp

@@ -34,6 +34,13 @@
 #ifndef V4L2_PIX_FMT_XBGR32
 #define V4L2_PIX_FMT_XBGR32  v4l2_fourcc('X', 'R', '2', '4')
 #endif
+#ifndef V4L2_PIX_FMT_Y16
+#define V4L2_PIX_FMT_Y16 v4l2_fourcc('Y', '1', '6', ' ')
+#endif
+#ifndef V4L2_PIX_FMT_Y16_BE
+#define V4L2_PIX_FMT_Y16_BE v4l2_fourcc_be('Y', '1', '6', ' ')
+#endif
+
 
 using namespace cv;
 
@@ -111,6 +118,7 @@ vector<Format_Channels_Depth> all_params = {
 //    { V4L2_PIX_FMT_SGBRG8, 1, CV_8U, 1.f, 1.f },
     { V4L2_PIX_FMT_RGB24, 3, CV_8U, 1.f, 1.f },
     { V4L2_PIX_FMT_Y16, 1, CV_16U, 1.f, 1.f },
+    { V4L2_PIX_FMT_Y16_BE, 1, CV_16U, 1.f, 1.f },
     { V4L2_PIX_FMT_Y10, 1, CV_16U, 1.f, 1.f },
     { V4L2_PIX_FMT_GREY, 1, CV_8U, 1.f, 1.f },
     { V4L2_PIX_FMT_BGR24, 3, CV_8U, 1.f, 1.f },