How can I extract color values from an EPS file?

Question

I'm trying to find all fill and stroke values used in an EPS file. I can parse the file, I just can't figure out how color values are defined in the EPS postscript section. I have converted the file to SVG (using ghostscript) and I can get the hex values, but an EPS to SVG conversion with a gradient produces files 20x the size. Is there a standard format for color values in postscript that I can extract from an EPS file?

Answer 1

PostScript is a programming language, not a simple file format, so there is no simple way to determine what is going on in the program.

A gradient may well be defined as a smooth shading in PostScript, which is a high level construct with no equivalent in SVG, so it will be rendered as an image (hence the explosion in size).

You can use the fact that PostScript is a programming language by redefining the basic operations, and using that to get the information you want. For example, to find the colour being used for a stroke you might do :

/OriginalStroke /stroke load def
/stroke {
(Current colour space = ) print currentcolorspace == flush
(current colour = ) print mark currentcolor counttomark -1 1 { -1 roll 20 string cvs print ( ) print} for flush pop
OriginalStroke
} bind def

Of course you will need to be prepared to cope with the rich variety of possible colour spaces in PostScript; Gray, RGB, CMYK, Separation, DeviceN, CIEBasedA, CIEBasedABC, CIEBasedDEF, CIEBasedDEFG, Indexed and Pattern.

Possibly you don';t need to know the original values, I'm guessing this is true because conversion to SVG will, I think, convert all colours to RGB, so perhaps you only want the RGB equivalents. In which case you could simply use:

(current colour in RGB = ) print currentrgbcolor 3 -1 roll == exch == == flush

I don't know how you wold handle a fill with a Pattern colour though :-)

Perhaps if you explained why you want to know this it would be easier to help.

Answer 2

the size of the bit image should not really matter if all you do is get a histogram and throw it away:

 pstopnm -stdout file.ps | ppmhist

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