Legacy ImageMagick Discussions Archive

I want to take an RGBA png input, extract the G & B channels, and pack them into a single 8-bit grayscale image. In other words the final 8-bit grayscale PNG output has the source Green channel packed into the lower 4 bits, the Blue channel packed into the upper 4 bits.

I can see how to extract the G and B channels as grayscale, but I'm stuck on scaling/biasing the channels to pack them together. Does anyone know if this is possible using the command line?

Cheers, Noel

It can probably be done entirely within IM, but possibly very messy. The easiest way would be to process the image in a script, C program or whatever.

Something similar was asked in this forum not long ago: viewtopic.php?f=2&t=23199

Thanks for the info. Looks like it'll be easier to write a standalone tool for this!

Yes, I think so. The RAW: and TXT: formats are easy to read and write. See http://www.imagemagick.org/Usage/files/#txt and http://www.imagemagick.org/Usage/formats/#rgb . Or PBM: http://www.imagemagick.org/Usage/formats/#pbmplus .

A C program to do what you want would be almost trivial.