Ticket #1384 (closed defect: fixed)

Opened 2 years ago

Last modified 1 year ago

Support TIFF files with improperly scaled colortable values

Reported by: izzybitsie@gmail.com Assigned to: warmerdam
Priority: normal Milestone: 1.4.1
Component: GDAL_Raster Version: unspecified
Severity: normal Keywords:
Cc:

Description (Last modified by hobu) 

"TIFF colors maps are supposed to have colors in the
range 0-65535 for each component instead of the usual 0-255 in other
formats.  If geotiff file has been incorrectly generated to
have the colormap between 0 and 255, GDAL converts it to
0-255 values (roughly by dividing by 256) so everything ends up black.
This may be a fairly common failure with tiff generators
and that some applications may have special logic to look for files
with all colormap values in the 0-255 range and avoid the rescaling
that should happen." Explanation offered by Frank Warmerdam to problem reported in gdal-dev forum.

Input image of the type mentioned can be downloaded from : http://www.mediamax.com/izzybitsie/Hosted/AS_GMSNO_00_20061122205548.tif.gz

When using gdal_merge.py to mosaic several images of this type a black map is obtained as output.

Change History

12/08/06 00:24:30 changed by warmerdam 

Updated summary to be more descriptive.

12/08/06 00:32:09 changed by warmerdam 

Updated colortable reading to look guess about the scaling problem, and
fix up on the fly if encountered.  Like this:

        int	nColorCount, nMaxColor = 0;
        GDALColorEntry oEntry;

        poColorTable = new GDALColorTable();

        nColorCount = 1 << nBitsPerSample;

        for( int iColor = nColorCount - 1; iColor >= 0; iColor-- )
        {
            oEntry.c1 = panRed[iColor] / 256;
            oEntry.c2 = panGreen[iColor] / 256;
            oEntry.c3 = panBlue[iColor] / 256;
            oEntry.c4 = 255;

            poColorTable->SetColorEntry( iColor, &oEntry );

            nMaxColor = MAX(nMaxColor,panRed[iColor]);
            nMaxColor = MAX(nMaxColor,panGreen[iColor]);
            nMaxColor = MAX(nMaxColor,panBlue[iColor]);
        }

        // Bug 1384 - Some TIFF files are generated with color map entry
        // values in range 0-255 instead of 0-65535 - try to handle these
        // gracefully.
        if( nMaxColor > 0 && nMaxColor < 256 )
        {
            CPLDebug( "GTiff", "TIFF ColorTable seems to be improperly scaled, fixing up." );
            
            for( int iColor = nColorCount - 1; iColor >= 0; iColor-- )
            {
                oEntry.c1 = panRed[iColor];
                oEntry.c2 = panGreen[iColor];
                oEntry.c3 = panBlue[iColor];
                oEntry.c4 = 255;
                
                poColorTable->SetColorEntry( iColor, &oEntry );
            }
        }

The problem file has been archived in data/geotiff/misc as:
 
   Bug1384_8bit_colortable.tif

01/05/07 00:00:11 changed by warmerdam 

Due to an unfortunate oversight on my part this change was not committed till
late January 4th 2007, and so it did not make it into GDAL 1.4.0 RC1, and
thus likely not into GDAL 1.4.0 final.

03/25/07 20:35:11 changed by hobu

  • status changed from closed to reopened.
  • resolution deleted.
  • description changed.

Will this one make it into 1.4.1?

03/25/07 21:49:01 changed by warmerdam

  • priority changed from highest to normal.
  • status changed from reopened to closed.
  • resolution set to fixed.
  • severity changed from blocker to normal.
  • milestone set to 1.4.1.

I have confirmed that this fix made it into the 1.4.1 branch.