From f0d2577482e258c54a3a2eed93722f51a92a25fc Mon Sep 17 00:00:00 2001
From: DRC <dcommander@users.sourceforge.net>
Date: Tue, 14 Dec 2010 01:21:29 +0000
Subject: [PATCH] Added extended tjDecompressHeader() function which can
 determine the type of subsampling used in the JPEG image

---
 turbojpeg.h  | 13 +++++++++++--
 turbojpegl.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/turbojpeg.h b/turbojpeg.h
index e80512b6..b9cb9b56 100644
--- a/turbojpeg.h
+++ b/turbojpeg.h
@@ -169,9 +169,9 @@ DLLEXPORT tjhandle DLLCALL tjInitDecompress(void);
 
 
 /*
-  int tjDecompressHeader(tjhandle j,
+  int tjDecompressHeader2(tjhandle j,
      unsigned char *srcbuf, unsigned long size,
-     int *width, int *height)
+     int *width, int *height, int *jpegsub)
 
   [INPUT] j = instance handle previously returned from a call to
      tjInitDecompress()
@@ -180,9 +180,18 @@ DLLEXPORT tjhandle DLLCALL tjInitDecompress(void);
   [INPUT] size = size of the JPEG image buffer (in bytes)
   [OUTPUT] width = width (in pixels) of the JPEG image
   [OUTPUT] height = height (in pixels) of the JPEG image
+  [OUTPUT] jpegsub = type of chrominance subsampling used when compressing the
+     JPEG image
 
   RETURNS: 0 on success, -1 on error
 */
+DLLEXPORT int DLLCALL tjDecompressHeader2(tjhandle j,
+	unsigned char *srcbuf, unsigned long size,
+	int *width, int *height, int *jpegsub);
+
+/*
+  Deprecated version of the above function
+*/
 DLLEXPORT int DLLCALL tjDecompressHeader(tjhandle j,
 	unsigned char *srcbuf, unsigned long size,
 	int *width, int *height);
diff --git a/turbojpegl.c b/turbojpegl.c
index 8e9605a7..0583a07f 100644
--- a/turbojpegl.c
+++ b/turbojpegl.c
@@ -86,6 +86,7 @@ typedef struct _jpgstruct
 
 static const int hsampfactor[NUMSUBOPT]={1, 2, 2, 1};
 static const int vsampfactor[NUMSUBOPT]={1, 1, 2, 1};
+static const int pixelsize[NUMSUBOPT]={3, 3, 3, 1};
 
 #define _throw(c) {sprintf(lasterror, "%s", c);  return -1;}
 #define _catch(f) {if((f)==-1) return -1;}
@@ -400,6 +401,60 @@ DLLEXPORT int DLLCALL tjDecompressHeader(tjhandle h,
 }
 
 
+DLLEXPORT int DLLCALL tjDecompressHeader2(tjhandle h,
+	unsigned char *srcbuf, unsigned long size,
+	int *width, int *height, int *jpegsub)
+{
+	int i, k;
+
+	checkhandle(h);
+
+	if(srcbuf==NULL || size<=0 || width==NULL || height==NULL || jpegsub==NULL)
+		_throw("Invalid argument in tjDecompressHeader()");
+	if(!j->initd) _throw("Instance has not been initialized for decompression");
+
+	if(setjmp(j->jerr.jb))
+	{  // this will execute if LIBJPEG has an error
+		return -1;
+	}
+
+	j->jsms.bytes_in_buffer = size;
+	j->jsms.next_input_byte = srcbuf;
+
+	jpeg_read_header(&j->dinfo, TRUE);
+
+	*width=j->dinfo.image_width;  *height=j->dinfo.image_height;
+	*jpegsub=-1;
+	for(i=0; i<NUMSUBOPT; i++)
+	{
+		if(j->dinfo.num_components==pixelsize[i])
+		{
+			if(j->dinfo.comp_info[0].h_samp_factor==hsampfactor[i]
+				&& j->dinfo.comp_info[0].v_samp_factor==vsampfactor[i])
+			{
+				int match=0;
+				for(k=1; k<j->dinfo.num_components; k++)
+				{
+					if(j->dinfo.comp_info[k].h_samp_factor==1
+						&& j->dinfo.comp_info[k].v_samp_factor==1)
+						match++;
+				}
+				if(match==j->dinfo.num_components-1)
+				{
+					*jpegsub=i;  break;
+				}
+			}
+		}
+	}
+
+	jpeg_abort_decompress(&j->dinfo);
+
+	if(*jpegsub<0) _throw("Could not determine subsampling type for JPEG image");
+	if(*width<1 || *height<1) _throw("Invalid data returned in header");
+	return 0;
+}
+
+
 DLLEXPORT int DLLCALL tjDecompress(tjhandle h,
 	unsigned char *srcbuf, unsigned long size,
 	unsigned char *dstbuf, int width, int pitch, int height, int ps,