2009.11.02 23:02 "Re: [Tiff] Tiffcrop test suite and logluv issues", by Toby Thain

On 2-Nov-09, at 4:59 PM, Richard Nolde wrote:

Every pixel shows at least one change for sample 0, a few pixels show multiple changes. Since tiffcp doesn't do anything but copy scanlines, unlike tiffcrop which loads the image into memory so that it can be manipulated, it is hard to figure out why the data would change unless,

as I suspect, the following code from tif_luv.c doesn't take into

consideration the fact that the original data is bigendian and I am

> compiling on a little endian host (having just gone through this with

Toby's patch suggestion.) In fact, running tiffcp or tiffcrop with the -B switch to generate big endian TIFF produces quite a different result for both off_luv24.tif and off_luv32.tif.

LogLuvDecode24(TIFF* tif, tidata_t op, tsize_t occ, tsample_t s)

{
         LogLuvState* sp = DecoderState(tif);
         int cc, i, npixels;
         unsigned char* bp;
         uint32* tp;

         assert(s == 0);
         assert(sp != NULL);

         npixels = occ / sp->pixel_size;

         if (sp->user_datafmt == SGILOGDATAFMT_RAW)
                 tp = (uint32 *)op;
         else {
                 assert(sp->tbuflen >= npixels);
                 tp = (uint32 *) sp->tbuf;
         }
                                         /* copy to array of uint32 */
         bp = (unsigned char*) tif->tif_rawcp;
         cc = tif->tif_rawcc;

          for (i = 0; i < npixels && cc > 0; i++) {
 bp[0] << 16 | bp[1] << 8 | bp[2];tp[i] =

^^ This is a portable way of decoding a 3-byte BigEndian value. It will work on any host.

--Toby

                  bp += 3;
                 cc -= 3;
         }