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I recently got a bunch of JPG photos but all are looking very strange colour wise – almost like colour negatives! My photo viewing program is saying they are all CMYK format but other ones which are looking OK are YCbCr format.

How can I batch change all CMYK photos to YCbCr with minimal loss of quality? (Windows command line solutions are fine.)

  • The problem you're running into is that there are two standards for CMYK JPEGs: the standard used by Adobe, and the standard used by everybody else. The two standards disagree on whether "100%" on a channel means fully-saturated or fully-unsaturated, with the result that files saved in a program using one standard will appear inverted when opened in a program using the other standard. – Mark Apr 18 '15 at 1:19
  • Just to confirm, is the reason you want to convert them just because they are displaying wrong for you on your software, or because you specifically need them in, say, sRGB (encoded as YCbCr) for purposes of printing/publishing/sharing them? Conversion from CMYK to RGB is lossy due to gamut differences, so you will lose some information most of the time (do the images exist in an RGB format anywhere, saved before their conversion to CMYK?). – thomasrutter Jun 17 '15 at 1:58
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I would do one of them manually in Photoshop (Image -> Mode -> RGB Color), then record an Action of the process https://helpx.adobe.com/photoshop/using/creating-actions.html. Then play the action back on the remaining images. If you need other steps, such as assigning a new color profile, resizing, etc., just record those as part of the action too.

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I am wondering what is your viewing program?

The information is giving you is a little strange, becouse YCbCr is a step in compressing jpg files, not a color model, which would be RGB, (and cmyk).

For a good conversion yo need a program that handles the cmyk files correctly, this is readint the colour profile embeded with it. If it has one.

You can use for example Irfanview (File > Batch Conversion Rename), or XnView (Tools > Batch Conversion) on Windows.

But there is a chance that your photos has no colour profile. In that case you need to use for example Photoshop and assign one, the one that looks better. You can download a 30 day trial from adobe.com

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