Legacy ImageMagick Discussions Archive

I would like to extract the quantization tables (also referred to as quantization matrices) from JPEG files, is it possible to do this with some imagemagick component?

Consider calling the JPEG delegate library API directly to extract the JPEG quantization tables. ImageMagick accesses them in the coder/jpeg.c module but they are not exported.

magick wrote:Consider calling the JPEG delegate library API directly to extract the JPEG quantization tables. ImageMagick accesses them in the coder/jpeg.c module but they are not exported.

Where can I find this library?

findus wrote:

magick wrote:Consider calling the JPEG delegate library API directly to extract the JPEG quantization tables. ImageMagick accesses them in the coder/jpeg.c module but they are not exported.

Where can I find this library?

Search google for libjpeg. or see http://www.imagemagick.org/download/delegates/

will do that for you.
djpeg is part of the libjpeg and the libjpeg-turbo (often through the libjpeg-turbo-progs package in linux) libraries.
If your chip supports libjpeg-turbo, you are generally better off using it.
Warning: the libjpeg API is not as stable as one would wish. libjpeg-turbo's is more stable, and explicitly documented as matching specific versions of the libjpeg library. The features of libjpeg that libjpeg-turbo does not implement are not really useful.