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My prospective printer demands a CMYK PDF. I have 40 PNGs to prepare (repeatedly). I convert an RGB PNG to a CMYK PDF with ImageMagick like this: convert myRGB.png -colorspace cmyk cmyk.pdf
The colors are not as bright in this pdf as they are if the same operation is done in Photoshop. I do not own Photoshop (a friend supplied the example). There is a web site that produces the same brighter result, but only one file at time. I need an open source solution like ImageMagick.
I have tried using several ICC profiles that I have downloaded from Adobe with the convert command like this: convert myRGB.png -colorspace cmyk -profile someAdobe.icc cmyk.pdf
But the results are identical. Can someone explain how to get brighter colors and also why the convert with -profile does not have any noticeable effect?
jsmithson
Posted 2016-08-07T18:08:20.807
Reputation: 11
'Bright' is not the aim, 'accurate' is the aim. Did you start from a calibrated source? If not, then you won't know what you've got til it gets back from the printer's anyway. – Tetsujin – 2016-08-07T18:14:20.450
Agreed with tetsujin. And they probably are using separate color matrices or depths for the conversion process. – Wyatt8740 – 2016-08-07T19:32:43.340
Yes, I agree bright is not the aim, accuracy is. I should have noted that the colors in the Photoshop PDF are a better match on the screen for the colors of the original PNG. Those are the colors we want to match and that the IM produced image does not match. But we are taking the examples to a printer today. Although my hopes are not high, I will report the results. The monitor is an off the shelf cheap 24". Probably not calibrated. – jsmithson – 2016-08-08T22:09:12.170
I have printed at a professional shop the original PNG, the Photoshop converted CMYK PDF, the IM converted RGB PDF, and the IM converted CMYK PDF. Only the IM CMYK PDF is darker. All the others closely match the screen display too, both on the cheap 24" and on a Mac 28". So I have to think there is something wrong with ImageMagick's conversion. – jsmithson – 2016-08-09T00:23:28.020