How to change background color of an eps file while converting it to jpeg or png

Question

I am converting eps (Encapsulated PostScript) files to jpeg files with ghostscript. A sample command I use is:

gswin32.exe -sDEVICE=jpeg -dJPEGQ=100 -dNOPAUSE -dBATCH -dSAFER -r600x600  -dGraphicsAlphaBits=4 -dUseCIEColor  -dEPSCrop -sOutputFile=”a.jpeg” b.eps

The input eps files come with white backgrounds (I only have their clipping path). What I need to do is change this white background to another color in the output images, or it would be even better if I could make them transparent (output file format would be png). How can I do this?

Answer 1

never tried it myself but you should be able to convert your eps file into png by setting:

-sDEVICE=pngalpha

also the pngalpha device has a -dBackgroundColor option:

-dBackgroundColor=16#RRGGBB (RGB color, default white = 16#ffffff) For the pngalpha device only, set the suggested background color in the PNG bKGD chunk. When a program reading a PNG file does not support alpha transparency, the PNG library converts the image using either a background color if supplied by the program or the bKGD chunk. One common web browser has this problem, so when using on a web page you would need to use -dBackgroundColor=16#CCCC00 when creating alpha transparent PNG images for use on the page.

more details here: Details of Ghostscript output devices see section 3.1. PNG file format

Answer 2

After you've obtained your (white background) images from Ghostscript, you could use ImageMagick's convert or GraphicMagick's gm convert commands to change the white to transparent background:

convert -background transparent my.png my_transp.png