[X] My Assistant

Note - I don't use photoshop, so I can't directly experiment or anything. All of the dialogs and comparisons I'm seeing are from GIMP.

I have an active bounty for cleaning a doujin. I'm being sent png files, and on opening I get told that the png has an embedded color profile ("Dot Gain 15%"), and am prompted to convert it to GIMP's internal greyscale working space. When I compare the cleaned image to the original, I can see a very slight change in the colors on the image, and I believe this is a result of that color profile.

Here's a diff, with the contrast turned way up: [i.imgur.com] https://i.imgur.com/SQAc0Sd.png
The text was edited, but everything else on the page should be showing up as black, as it shouldn't have been modified. Instead an outline of the artwork is visible.

From my understanding, color profiles are intended for printing, and dealing with different paper/printer/inks that may result in darker/lighter appearing colors in the real world. This is digital-only, so I shouldn't need any of this.

How can I avoid this profile stuff? Is it possible to prevent the profile from being added on export? The bounty hunter did some experiments and produced PNGs without the "embedded color profile" popup, but this resulted in an image that was significantly darker than the original, not just "slightly" different. Does something need to be done differently when importing the original file? If it matters, the originals are 32-color indexed PNGs.

Original image: https://e-hentai.org/s/e86db8f7a2/756433-5
Archive of some experiments with exporting from PS (diff was made with "pachupachu05.png"; "-final.png" is identical to the original (except RGB color mode). All others are visibly darker than the original image)

Dot gain is a measurement of how the color of a printed image differs from the digital RGB values. (Because printers don't print solid colors, just a grid of super dense dots that don't perfectly replicate the digital colors.)

The color profile here attempts to replicate the printed appearance of your image in your editing program by modifying the displayed RGB values (not the values of the image file, just the monitor).

Soooo the takeaway is that you should disable any dot-gain related settings (in Photoshop, you can do this by switching to "sGray" in color settings). As a sanity check, you could screenshot your image when its opened in GIMP and compare the color of a pixel in the screenshot to the color dropper measurement in GIMP. They should match up if there's no profile fuckery.

And yes, you can disable the profile from being included in the image in the export menu (not sure about GIMP).

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(Also, someone please correct me if I'm wrong on anything. I nearly melted my brain last time I went into ICC profiles / color spaces / etc).

This post has been edited by 프레이: Aug 5 2020, 20:50

Thanks, that seems to have done it. I believe he's using sRGB followed by a conversion to indexed color, but the effect seems to be the same. I assume those are photoshop's "Digital" profiles.

Another option is for me to convert the images to greyscale mode in GIMP myself; it does seem to be the Index->Grey conversion that was breaking things, and GIMP apparently doesn't insert a profile by default.