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August 2007
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2007.08.07 15:41 "Re: Indexed Images", by Toby Thain
On 7-Aug-07, at 12:23 PM, Frank Warmerdam wrote:
> 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.
Disclaimer: I'm much more familiar with C than C++, but why would
taking the address of the vector.front() element have the meaning as
taking &array[0]? Or should I just RTFM? :-)
--Toby
> 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,
> --
> ---------------------------------------
> +--------------------------------------
> I set the clouds in motion - turn up | Frank Warmerdam,
> warmerdam@pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush | President OSGeo, http://
> osgeo.org
>
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