ImageMagick changes colors when converting PDF to images

Question

I am converting various PDFs uploaded by end users into images using following command

-density 140 -limit memory 64MB -limit map 128MB [pdffile] page.png

Here is the result. On the right we have original PDF and on the left output image. As you can see the colors are quite noticeably different.

What could be causing this and how fix it?

Answer 1

try following command:

-density 140 -limit memory 64MB -limit map 128MB -colorspace RGB [pdffile] page.png

Answer 2

Edit: I later discovered that ImageMagick can do it fine, I just needed to use -colorspace sRGB

My final command was:

convert -density 560 -limit memory 64MB -limit map 128MB \
        -colorspace sRGB [pdffile] -scale 25% page.png

The oversampling and scaling down was to counter the poor anti-aliasing mentioned below.

Before I discovered that, here was my earlier solution...

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In my case the colors produced by ImageMagick's convert were oversaturated, quite like those in the question. I was trying to convert this file using IM 6.7.7.10-6ubuntu3.

• -resample 100 made no difference.

• -colorspace RGB seemed to produce more accurate saturations, but the entire image was darker than it should have been.

Curiously, this suggestion to use GhostScript instead of ImageMagick for the conversion, produced very close to the correct colors:

gs -q -sDEVICE=png16m -dSubsetFonts=true -dEmbedAllFonts=true \
      -sOutputFile=page.png -r200 -dBATCH -dNOPAUSE [pdffile]

(The original suggestion passed the -dUseCIEColor option, but in my case this appeared to reduce the gamma: light pixels were fine, but the dark pixels were too dark, so I removed it.)

After that, the only thing that bothered me was that the anti-aliasing/edges were a little off in places (especially visible on curves passing 45 degrees). To improve that, I created the output at four times the required resolution, and then scaled down afterwards, rendering those errors almost imperceptible. Note that I had to use ImageMagick's -scale for this, and not -geometry or -resize, in order to avoid bicubic ringing effects.