add a -yuv option to dwebp (very similar to -pgm)

It will decode to raw (flat) YUV format, similar to what
cwebp can take as input. Makes the PSNR/SSIM calculation easier.

Change-Id: Iebfaedfc0bedc70c169b24ae4aabc701488d0644

README

@@ -240,6 +240,8 @@ Use following options to convert into alternate image formats:
   -ppm ......... save the raw RGB samples as a color PPM
   -pgm ......... save the raw YUV samples as a grayscale PGM
                  file with IMC4 layout.
+  -yuv ......... save the raw YUV samples in flat layout.
+
  Other options are:
   -version  .... print version number and exit.
   -nofancy ..... don't use the fancy YUV420 upscaler.

examples/dwebp.c

@@ -62,6 +62,7 @@ typedef enum {
   PAM,
   PPM,
   PGM,
+  YUV,
   ALPHA_PLANE_ONLY  // this is for experimenting only
 } OutputFileFormat;
 
@@ -238,33 +239,51 @@ static int WriteAlphaPlane(FILE* fout, const WebPDecBuffer* const buffer) {
   return 1;
 }
 
-static int WritePGM(FILE* fout, const WebPDecBuffer* const buffer) {
+// format=PGM: save a grayscale PGM file using the IMC4 layout
+// (http://www.fourcc.org/yuv.php#IMC4). This is a very convenient format for
+// viewing the samples, esp. for odd dimensions.
+// format=YUV: just save the Y/U/V/A planes sequentially without header.
+static int WritePGMOrYUV(FILE* fout, const WebPDecBuffer* const buffer,
+                         OutputFileFormat format) {
   const int width = buffer->width;
   const int height = buffer->height;
   const WebPYUVABuffer* const yuv = &buffer->u.YUVA;
-  // Save a grayscale PGM file using the IMC4 layout
-  // (http://www.fourcc.org/yuv.php#IMC4). This is a very
-  // convenient format for viewing the samples, esp. for
-  // odd dimensions.
   int ok = 1;
   int y;
+  const int pad = (format == YUV) ? 0 : 1;
   const int uv_width = (width + 1) / 2;
   const int uv_height = (height + 1) / 2;
-  const int out_stride = (width + 1) & ~1;
+  const int out_stride = (width + pad) & ~pad;
   const int a_height = yuv->a ? height : 0;
-  fprintf(fout, "P5\n%d %d\n255\n", out_stride, height + uv_height + a_height);
+  if (format == PGM) {
+    fprintf(fout, "P5\n%d %d\n255\n",
+            out_stride, height + uv_height + a_height);
+  }
   for (y = 0; ok && y < height; ++y) {
     ok &= (fwrite(yuv->y + y * yuv->y_stride, width, 1, fout) == 1);
+    if (format == PGM) {
       if (width & 1) fputc(0, fout);    // padding byte
     }
+  }
+  if (format == PGM) {   // IMC4 layout
     for (y = 0; ok && y < uv_height; ++y) {
       ok &= (fwrite(yuv->u + y * yuv->u_stride, uv_width, 1, fout) == 1);
       ok &= (fwrite(yuv->v + y * yuv->v_stride, uv_width, 1, fout) == 1);
     }
+  } else {
+    for (y = 0; ok && y < uv_height; ++y) {
+      ok &= (fwrite(yuv->u + y * yuv->u_stride, uv_width, 1, fout) == 1);
+    }
+    for (y = 0; ok && y < uv_height; ++y) {
+      ok &= (fwrite(yuv->v + y * yuv->v_stride, uv_width, 1, fout) == 1);
+    }
+  }
   for (y = 0; ok && y < a_height; ++y) {
     ok &= (fwrite(yuv->a + y * yuv->a_stride, width, 1, fout) == 1);
+    if (format == PGM) {
       if (width & 1) fputc(0, fout);    // padding byte
     }
+  }
   return ok;
 }
 
@@ -299,8 +318,8 @@ static void SaveOutput(const WebPDecBuffer* const buffer,
     ok &= WritePPM(fout, buffer, 1);
   } else if (format == PPM) {
     ok &= WritePPM(fout, buffer, 0);
-  } else if (format == PGM) {
-    ok &= WritePGM(fout, buffer);
+  } else if (format == PGM || format == YUV) {
+    ok &= WritePGMOrYUV(fout, buffer, format);
   } else if (format == ALPHA_PLANE_ONLY) {
     ok &= WriteAlphaPlane(fout, buffer);
   }
@@ -326,6 +345,8 @@ static void Help(void) {
          "  -ppm ......... save the raw RGB samples as a color PPM\n"
          "  -pgm ......... save the raw YUV samples as a grayscale PGM\n"
          "                 file with IMC4 layout.\n"
+         "  -yuv ......... save the raw YUV samples in flat layout.\n"
+         "\n"
          " Other options are:\n"
          "  -version  .... print version number and exit.\n"
          "  -nofancy ..... don't use the fancy YUV420 upscaler.\n"
@@ -385,6 +406,8 @@ int main(int argc, const char *argv[]) {
       return 0;
     } else if (!strcmp(argv[c], "-pgm")) {
       format = PGM;
+    } else if (!strcmp(argv[c], "-yuv")) {
+      format = YUV;
     } else if (!strcmp(argv[c], "-mt")) {
       config.options.use_threads = 1;
     } else if (!strcmp(argv[c], "-crop") && c < argc - 4) {
@@ -450,6 +473,7 @@ int main(int argc, const char *argv[]) {
         output_buffer->colorspace = MODE_RGB;  // drops alpha for PPM
         break;
       case PGM:
+      case YUV:
         output_buffer->colorspace = bitstream->has_alpha ? MODE_YUVA : MODE_YUV;
         break;
       case ALPHA_PLANE_ONLY:

man/dwebp.1

@@ -1,5 +1,5 @@
 .\"                                      Hey, EMACS: -*- nroff -*-
-.TH DWEBP 1 "August 2, 2012"
+.TH DWEBP 1 "January 28, 2013"
 .SH NAME
 dwebp \- decompress a WebP file to an image file
 .SH SYNOPSIS
@@ -31,9 +31,15 @@ Change the output format to PAM (retains alpha).
 Change the output format to PPM (discards alpha).
 .TP
 .B \-pgm
-Change the output format to PGM. The output consist of luma/chroma
+Change the output format to PGM. The output consists of luma/chroma
 samples instead of RGB, using the ICM4 layout. This option is mainly
-for verification and debugging purpose.
+for verification and debugging purposes.
+.TP
+.B \-yuv
+Change the output format to raw YUV. The output consists of
+luma/chroma-U/chroma-V samples instead of RGB, saved sequentially as
+individual planes. This option is mainly for verification and debugging
+ purposes.
 .TP
 .B \-nofancy
 Don't use the fancy upscaler for YUV420. This may lead to jaggy