Added extended tjDecompressHeader() function which can determine the type of subsampl...

git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@310 632fc199-4ca6-4c93-a231-07263d6284db

diff --git a/turbojpeg.h b/turbojpeg.h
index e80512b637bb37636b4850697422e43e28ab3df5..b9cb9b560871477f9b5a0068b775b61cf22a82e7 100644 (file)
--- 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 8e9605a7cafc121070597fd7e417fd0207048d9b..0583a07fe8349b7fc7381291ab9171374cd0e6dd 100644 (file)
--- 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,