From 8ea0da109c1e8134b123f618b5e7df5274183e87 Mon Sep 17 00:00:00 2001
From: Bent Bisballe Nyeng <deva@aasimon.org>
Date: Fri, 19 Sep 2014 17:44:44 +0200
Subject: YUYV -> JPEG conversion (untested).

---
 src/v4l.cc | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 92 insertions(+), 3 deletions(-)

diff --git a/src/v4l.cc b/src/v4l.cc
index 7d8ed3f..c83da06 100644
--- a/src/v4l.cc
+++ b/src/v4l.cc
@@ -44,6 +44,13 @@
 
 #include <linux/videodev2.h>
 
+extern "C" {
+#include <jpeglib.h>
+}
+
+#define JPEG_HEADER_PAD 500
+
+static bool isYUYV = false;
 static V4L *v4l = NULL;
 
 #define CLEAR(x) memset(&(x), 0, sizeof(x))
@@ -85,9 +92,86 @@ static int xioctl(int fh, int request, void *arg)
   return r;
 }
 
+/*
+ * In typical computer APIs, "YUV" actually means YCbCr, and "YUYV" means
+ * "YCbCr 4:2:2" stored as Y0, Cb01, Y1, Cr01, Y2 ...
+ */
+static void toJpeg(int quality, unsigned char *yuyv,
+                   int image_width, int image_height,
+                   char **out, size_t *size)
+{
+  JSAMPLE *image_buffer = (JSAMPLE*)yuyv;
+
+  long unsigned int buffersize =
+    (image_width * image_height * 3) + JPEG_HEADER_PAD;
+  unsigned char *jpeg_output_buffer = (unsigned char *)malloc(buffersize);
+  struct jpeg_compress_struct cinfo;
+  struct jpeg_error_mgr jerr;
+    
+  JSAMPROW row_pointer[1];      // pointer to JSAMPLE row[s] 
+  int row_stride;               // physical row width in image buffer 
+    
+  // Allocate and initialize JPEG compression object 
+  cinfo.err = jpeg_std_error(&jerr);
+  jpeg_create_compress(&cinfo);
+    
+  // Specify data destination (see jpeg_mem_dest)
+  jpeg_mem_dest(&cinfo, &jpeg_output_buffer, &buffersize);
+    
+  // Set compression parameters
+  cinfo.image_width = image_width;      // image width and height, in pixels 
+  cinfo.image_height = image_height;
+  cinfo.input_components = 3;           // # of color components per pixel 
+  cinfo.in_color_space = JCS_RGB;       // colorspace of input image 
+    
+  jpeg_set_defaults(&cinfo);
+    
+  jpeg_set_quality(&cinfo, quality, TRUE); // limit to baseline-JPEG values
+    
+  // Start compressor 
+  jpeg_start_compress(&cinfo, TRUE);
+    
+  // While (scan lines remain to be written) 
+  row_stride = image_width * 3; // JSAMPLEs per row in image_buffer 
+
+  unsigned char *yuv = new unsigned char[image_width * 3]; 
+  while (cinfo.next_scanline < cinfo.image_height) {
+     for (int i = 0; i < cinfo.image_width; i += 2) { 
+        yuv[i*3]   = yuyv[i*2]; 
+        yuv[i*3+1] = yuyv[i*2+1]; 
+        yuv[i*3+2] = yuyv[i*2+3]; 
+        yuv[i*3+3] = yuyv[i*2+2]; 
+        yuv[i*3+4] = yuyv[i*2+1]; 
+        yuv[i*3+5] = yuyv[i*2+3]; 
+    } 
+    row_pointer[0] = yuv; 
+    yuyv += image_width * 2;
+    jpeg_write_scanlines(&cinfo, row_pointer, 1);
+
+    //    row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride];
+    //    (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
+  }
+  delete[] yuv;
+
+  // Finish compression 
+  jpeg_finish_compress(&cinfo);
+
+  // Release JPEG compression object 
+  jpeg_destroy_compress(&cinfo);
+
+  *size = buffersize;
+  *out = (char*)jpeg_output_buffer;
+}
+
 static void process_image(const void *p, int size)
 {
-  if(v4l) v4l->processImage(p, size);
+  const void *img = p;
+  int img_size = size;
+
+  if(isYUYV) {
+    toJpeg(70, (unsigned char*)p, 640, 480, (char**)&img, (size_t*)&img_size);
+  }
+  if(v4l) v4l->processImage(img, img_size);
   /*
   if (out_buf)
     fwrite(p, size, 1, stdout);
@@ -528,10 +612,15 @@ static void init_device(void)
     format[4] = '\0';
     printf("format: %s\n", format);
     if(strcmp(format, "JPEG")) {
-      printf("Webcam does not support JPEG...!\n");
-      exit(1);
+      if(strcmp(format, "YUYV")) {
+        printf("Webcam neither supports JPEG nor YUYV...!\n");
+        exit(1);
+      } else {
+        isYUYV = true; // Activate libJPEG encoding on each frame.
+      }
     }
 
+
     /* Note VIDIOC_S_FMT may change width and height. */
   } else {
     /* Preserve original settings as set by v4l2-ctl for example */
-- 
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