jpg-artifacts increase after color conversion

New Here ,
Feb 06, 2018 Feb 06, 2018

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Hi

Why do the jpg-artifacts increase when I make a color conversion? They do increase independent on the rendering intent. Does Acrobat make a recompression in the background?

Bildschirmfoto 2018-02-06 um 12.55.56.png

image before conversion

Bildschirmfoto 2018-02-06 um 12.56.49.png

image after conversion

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Macintosh, Print and prepress

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LEGEND ,
Feb 06, 2018 Feb 06, 2018

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Of course... to colour convert JPEG compressed data, in must first be decompressed, then colour converted. It is likely then recompressed. Why do you convert?

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New Here ,
Feb 07, 2018 Feb 07, 2018

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Thank you.

The color conversion is part of a correction profile I made to correct incoming print-files. So we receive a lot of them with more than 300% ink coverage we have to do a color conversion.

The problem I was writing about we only have with images they have jpg-artifacts. But the artifacts increase a lot, so you can see them in the print output.

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Adobe Community Professional ,
Feb 06, 2018 Feb 06, 2018

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You have a JPEG image open and do a colour conversion. Then you see on-screen more or stronger artefacts? No, there is only the colour conversion who modifies the existing artefacts and unfortunately they get more visible.

You have a JPEG image open and then save the image again to JPEG. Each open-save-cycle, even without modification adds to the artefacts.

If you do that via Acrobat, Acrobat does the colour conversion, and you will eventually see more artefacts. Then it resaves the image as a JPEG  which adds again to the artefacts.

ABAMBO | Hard- and Software Engineer | Photographer

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LEGEND ,
Feb 06, 2018 Feb 06, 2018

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I think, Abambo, that what you right is absolutely correct in Photoshop and other apps like it. But it cannot be how PDF files are colour converted, and I take this to be a question about Acrobat.

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Adobe Community Professional ,
Feb 07, 2018 Feb 07, 2018

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Paragraph 1&2 are JPEG basics, paragrah 3 is what happens in Acrobat. Acrobat does not change the basics.

ABAMBO | Hard- and Software Engineer | Photographer

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New Here ,
Feb 07, 2018 Feb 07, 2018

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Thank you all.

I think there is a problem in acrobat. When I do the conversion in photoshop so I dont get any visible increase of the jpg-artifacts. Even when I make several save as jpg-steps.

So i still dont understand why the artifacts increases when I do the conversion in Acrobat DC.

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Adobe Community Professional ,
Feb 07, 2018 Feb 07, 2018

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Photoshop and Acrobat are bound by the technical limitations of all the factors that increase the artefacts. The only real difference is that Photoshop offers a better control for the parameters. (It may also be that algorithms are better implemented with Photoshop).

Until now I havn’t seen substantial degradations during conversation except when I voluntarly lowered the quality factor.

ABAMBO | Hard- and Software Engineer | Photographer

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Community Beginner ,
Jan 27, 2021 Jan 27, 2021

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We have the same problem, but no JPG involved:

1) we get UNCOMPRESSED 4C images in a PDF/X-4 file (no JPG in export settings). There are no JPG artifacts in the images.

2) we run a conversion of colors in Acrobat to a different profile (actually changing th CMYK values)

3) the saved PDF file has heavy JPG artifacts visible ... (also, the file size is far smaller after the conversion, indicating there is lossy compression going on).

---> the image quality is defacto unusable.

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