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So, I know that this question has already been answered before, however, the steps to actually create the image (the black cat/white cat image) were pretty unclear and it might also be somewhat outdated by now. Apparently you need to adjust the color levels of whatever two images you want to use to "satisfy the relative lightness condition a ≤ b" but it doesn't actually say how to do that. So if anyone could explain step-by-step how to create a PNG that looks like either the first or the second image I've provided down below depending on whether the background color is black or white using either GIMP or Photoshop, I'd be very happy. (Keep in mind that I'm pretty much a beginner at both GIMP and Photoshop, so please explain in detail what to do, what buttons to click, etc.)

enter image description hereenter image description here

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  • Hi. Welcome to GDSE. The answer in the question you linked to already has a step by step guide. Ignore the maths and lengthy explanation. Just do the steps listed under "Now I'll do the following steps". It works in Photoshop, I just tested it. The instructions aren't outdated, although they aren't probably easy for a beginner to understand.
    – Billy Kerr
    Sep 22, 2020 at 19:43
  • What I suggest you do is learn to walk before you try to run. Once you've learnt the basics of raster image editing, then the steps will make sense.
    – Billy Kerr
    Sep 22, 2020 at 19:55
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    Does this answer your question? Image that looks different on black background and on white
    – Wolff
    Sep 22, 2020 at 19:56
  • Hi there and welcome to GDSE! I vote to close this as well as I can confirm that the method in the other question works, just tried it. I was a little confused in the fourth step: "use the channels dialog to transfer it to the selection". It means "switch to the Channels panel and Ctrl/Cmd + left-click the RGB channel to create a selection".
    – Wolff
    Sep 22, 2020 at 20:01
  • Also just to say, part of the confusion here may lie in doing levels adjustments first. Basically what that means is you need to do a levels adjustment on each image to make one bright, and one dark, otherwise the final result won't be so good.
    – Billy Kerr
    Sep 22, 2020 at 20:15

1 Answer 1

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What it means is that you need to do a levels adjustment on the images so that one is bright, and the other dark. There's no specific setting. You can just eyeball it. This is so that you won't see ghosting of the two images together. The starker the brightness difference, the better the result.

So for example, here are your two images with some levels adjustments

enter image description here

And here is the finished result showing the final edit over a white and black background.

enter image description here

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    I tried doing a levels adjustment on the images by making one of them darker and the other one brighter, like you did, and I got the result that I wanted. Thank you so much!
    – Rallve
    Sep 22, 2020 at 20:38
  • You're welcome. Glad it worked for you.
    – Billy Kerr
    Sep 22, 2020 at 20:38
  • If you want to make sure that absolutely none of the black image is visible on the white and vice versa you can set Levels > Output Levels to 0, 128 on the black image and 128, 255 on the white image. Result
    – Wolff
    Sep 22, 2020 at 21:12
  • @Wolff - cool!!!!!!!
    – Billy Kerr
    Sep 22, 2020 at 21:27

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