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This is really throwing me for a loop. For some reason, when I copy and paste a portion of an image in a document (with an embedded colour profile), the pasted image is a different colour than the copied image.

Here's how I'm testing it:

  1. Select an arbitrary rectangle
  2. Copy
  3. Paste
  4. Command-click new layer to select the rectangle
  5. Select other layer and delete

(I'm doing steps 4 and 5 because the image is semitransparent)

This results in a clearly visible rectangle differentiating the pasted image from the original. The pasted image is slightly (but very noticeably) darker.

I've tried changing the colour profile settings around including all three options of disable, preserve and convert, and there is no discernible difference to any of those options. Exactly the same result: clearly darker pasted rectangle.

I don't get it. What am I missing?

Note: This appears to only happen for semitransparent images, I just noticed. When I do it to a solid-colour image it looks perfect.

  • Have you compared the color values of the two rectangles to see if they are different colors? The difference in appearance may be from one being highlighted or on the current layer, or one is under a transparency mask. The color values will tell the true story. – Webster Jul 31 '17 at 20:41
  • @Webster In fact the colour codes are identical. It appears to be the alpha that is messed up. Yes they are definitely different: 87% on the pasted image, 85% on the original. – devios1 Jul 31 '17 at 20:44
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    I've never been Thrown for a loop, sounds fun. – Digital Lightcraft Aug 1 '17 at 7:50
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    Any chance of a screen shot? Surely if they are semi-transparent, the background will affect the colour? – Digital Lightcraft Aug 1 '17 at 7:52
  • @DigitalLightcraft It is indeed a screenshot, however one taken of a window using Cmd-Shift-4 + Spacebar, which generates a PNG of just the window, including the transparent shadow. – devios1 Aug 1 '17 at 13:48
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I think this all comes from the fact that your image is semi-transparent and a confusion of how selections work...

You're first copy/pasting a semi-transparent image. Overlaying a semi-transparent image on itself will inevitably make the image darker. That's just how transparency works; overlay two semi-transparent solid rectangles and you'll see the intersection is darker.

You're then making a selection from a semi-transparent image, but your selection isn't an opaque rectangle; it is also semi-transparent. Using that selection on another layer will only affect that layer as much as is selected. So if you make an 80% opaque selection, that will only delete (or whatever else) 80% of the layer you are using it on. If the layer you are using it on is also 80% opaque, then it will only affect 80% of that 80%, not 100%...

As an example, take these two 80% opaque squares:

enter image description here

Note, they were drawn at 80% opacity; so the pixels themselves are 80% opaque, the layers themselves are at 100% opacity.

We cmd+click the top layer to make a selection, then use that selection to delete pixels from the lower layer. Only 80% of the transparency of that layer is deleted:

enter image description here

So even after deleting the from the lower layer with the selection made from the top layer, there is still the darker intersection:

enter image description here

I'm not entirely sure what the desired outcome is here, but if you want a fully opaque selection from a semi-transparent layer then you're better off using the regular selection tools rather than making the selection from the layer itself.

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  • I don't understand why cmd-clicking includes alpha. I had no idea it would do that, it doesn't make sense to me. When would I ever want to select a portion of the alpha? That must be it, it does look a lot like your bottom image what is happening. The reason I cmd-clicked was to perfectly select the layer's bounds. – devios1 Aug 1 '17 at 12:30
  • I just tested it and you are absolutely correct: if I select, copy, and delete before pasting, it looks perfect. You learn something new every day! Now if only I could figure out WHY it includes alpha, because that still makes zero sense to me. – devios1 Aug 1 '17 at 13:51
  • Well, it doesn't just include alpha; it is the alpha channel of the layer your making the selection from. It can be confusing when you're just using it to get the bounds of a layer but it makes sense as long as you keep in mind that's what it is – Cai Aug 1 '17 at 13:55
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    It's actually still useful for it to use the alpha channel even when you're selecting a solid layer, otherwise you'll get an aliased (i.e. jagged edges) selection from anything non-rectangular – Cai Aug 1 '17 at 13:56
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Semi-transparent objects react different on each color backgrounds. Try putting colored rectangle that matches background underneath the copied semi-transparent one.

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