Hi
I found that .gp4 is a CCITT Group 4 File,used for fax,and .cal is CALS Raster Graphics,1bit black and white image.Now,I take it that you are trying something to do with faxes or something.A good place to start looking for details about .gp4 and .cal file formats is some site that has technical documentation on these formats,possibly a CCITT site.There you find and read the documentation,and start writing your code.You picked such formats,that no one has written a program that works with these files,and therefore no one has posted code or something.Taking into account that CCITT is in question,posibly there .gp4 and .cal are protected with patents,and you may have to purchase technical documentation from CCITT.
Cheers
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