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August 2007
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2007.08.07 15:23 "Re: Indexed Images", by Frank Warmerdam
Christian Henning wrote:
> Hi there, I'm trying to write a 4-bit indexed image using libtiff
> 3.8.2 on a Windows machine. For some reasons writing the color map
> always crashes and I have no idea why. Here is my code, it's very
> straight forward:
>
> int main()
> {
> tsize_t width = 100;
> tsize_t height = 100;
> tsize_t bits_per_sample = 4;
> tsize_t samples_per_pixel = 1;
>
> tsize_t image_size_in_bytes = ( width * height ) / 2;
> tsize_t palette_size = 16 * 3;
>
> TIFF* file = TIFFOpen( "palette.tif", "w" );
>
> TIFFSetField( file, TIFFTAG_IMAGEWIDTH , width );
> TIFFSetField( file, TIFFTAG_IMAGELENGTH , height );
> TIFFSetField( file, TIFFTAG_BITSPERSAMPLE , bits_per_sample );
> TIFFSetField( file, TIFFTAG_SAMPLESPERPIXEL, samples_per_pixel );
> TIFFSetField( file, TIFFTAG_ROWSPERSTRIP , height );
>
> std::vector< short > palette( palette_size );
> std::fill( palette.begin(), palette.end(), 0 );
>
> TIFFSetField( file, TIFFTAG_COLORMAP, &palette.front() );
>
>
> std::vector< unsigned char > image( image_size_in_bytes );
> std::fill( image.begin(), image.end(), 0 );
>
> TIFFWriteEncodedStrip( file
> , 0
> , &image.front()
> , image_size_in_bytes );
>
> TIFFClose( file );
> }
>
> Can anyone tell me why the line
>
> TIFFSetField( file, TIFFTAG_COLORMAP, &palette.front() );
>
> always crashes?
Christian,
Because TIFFSetField() expects three short arrays as an argument for
key TIFFTAG_COLORMAP. (red, green and blue portions of the palette).
Contrary to what Toby says, I'm fairly confident that taking the address
of the reference returned by palette.front() should work. Oddly, I
setup some similar code just last night using std::vector<> for TIFF
palettes. A simple example of passing three short arrays looks like
this:
TIFFSetField( hTIFF, TIFFTAG_COLORMAP, anTRed, anTGreen, anTBlue );
Best regards,
--
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I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com
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