Merge pull request #90 from sparrowwallet/convert-yu12

Add YU12 to RGB conversion on Linux

Author: vonnieda

linux/platformstream.cpp

@@ -556,6 +556,15 @@ void PlatformStream::threadSubmitBuffer(void *ptr, size_t bytes)
             m_frames++;
             m_bufferMutex.unlock();
             break;
+        case V4L2_PIX_FMT_YUV420:
+            // YU12 to RGB conversion
+            // YU12 has 1.5 bytes per pixel (12 bits), RGB has 3 bytes per pixel
+            m_bufferMutex.lock();
+            YU122RGB((const uint8_t*)ptr, &m_frameBuffer[0], m_width, m_height);
+            m_newFrame = true;
+            m_frames++;
+            m_bufferMutex.unlock();
+            break;
         case 0x47504A4D:    // MJPG
             #ifdef FRAMEDUMP
             {

linux/yuvconverters.cpp

@@ -123,3 +123,56 @@ void NV122RGB(const uint8_t *nv12, uint8_t *rgb, uint32_t width, uint32_t height
         }
     }
 }
+
+/*
+    YU12 (I420) format has three planes:
+    - Y plane: Full resolution luminance samples
+    - U plane: 2x2 subsampled U (Cb) samples
+    - V plane: 2x2 subsampled V (Cr) samples
+
+    Memory layout:
+    YYYYYYYY
+    YYYYYYYY
+    YYYYYYYY
+    YYYYYYYY
+    UUUU
+    UUUU
+    VVVV
+    VVVV
+
+    Each 2x2 Y block shares one U and one V value.
+*/
+void YU122RGB(const uint8_t *yu12, uint8_t *rgb, uint32_t width, uint32_t height)
+{
+    const uint8_t *y_plane = yu12;
+    const uint8_t *u_plane = yu12 + (width * height);
+    const uint8_t *v_plane = u_plane + (width * height / 4);
+
+    for (uint32_t row = 0; row < height; row++)
+    {
+        for (uint32_t col = 0; col < width; col++)
+        {
+            // Get Y value for current pixel
+            int16_t y = y_plane[row * width + col];
+
+            // Get U,V values (shared by 2x2 pixel blocks)
+            uint32_t uv_row = row / 2;
+            uint32_t uv_col = col / 2;
+            uint32_t uv_index = uv_row * (width / 2) + uv_col;
+
+            int16_t u = u_plane[uv_index];  // Cb
+            int16_t v = v_plane[uv_index];  // Cr
+
+            // Convert YUV to RGB using the same coefficients as YUYV
+            int16_t yy = 19 * (y - 16);
+
+            // Calculate RGB index
+            uint32_t rgb_index = (row * width + col) * 3;
+
+            // R, G, B order (RGB24)
+            rgb[rgb_index]     = clamp((yy + 26 * (v - 128)) >> 4);
+            rgb[rgb_index + 1] = clamp((yy - 13 * (v - 128) - 6 * (u - 128)) >> 4);
+            rgb[rgb_index + 2] = clamp((yy + 32 * (u - 128)) >> 4);
+        }
+    }
+}

linux/yuvconverters.h

@@ -35,5 +35,6 @@
 
 void YUYV2RGB(const uint8_t *yuv, uint8_t *rgb, uint32_t bytes);
 void NV122RGB(const uint8_t *nv12, uint8_t *rgb, uint32_t width, uint32_t height);
-
+void YU122RGB(const uint8_t *yu12, uint8_t *rgb, uint32_t width, uint32_t height);
+    
 #endif