color shift after merged copy in the same file

[defaults43mynahcjra]

Hello- I work in PSB files with many layers. When I copy merged (cmd, shift c) and paste within the same file (as a top layer), i get a significant color shift (it appears mostly a lot lighter). As its pasted back in the same file, there should no profile conflict, right?  Im in working RGB, but it happens also in adobe rgb, CMYK etc. It seems to only happen in the files with many layers. Any ideas?

[D Fosse · Accepted solution]

I'm guessing this is an image that has very noisy and/or binary elements? View at 100% to get a correct preview before merging.

Whenever something seems to change when merging layers, it's because you are not viewing at 100%. The merged result is correct. The preview is misleading and incorrect.

100% in Photoshop has nothing to do with size. It means one image pixel is represented by exactly one physical screen pixel.

For performance reasons, all blending and adjustment previews are calculated on the on-screen version of the image. When you are zoomed out, that means a resampled and softened version of the image. Pixel levels are averaged out. You get a lot of intermediate values that aren't there in the full original data.

When you merge, commit an adjustment etc, the numbers are re-calculated on the full original data, pixel for pixel.

Viewing at 100% avoids all this and renders the whole issue moot. You see every pixel before and after, and so nothing changes.

[defaults43mynahcjra]

Spot-on answer! Thank you

SOLVED

[Harmonious_shape5FF9]

is there ANY way to turn off this thing that makes photoshop show this "resampled and softened version of the image"?

[D Fosse]

Ctrl+1, View > 100%, which represents one image pixel by exactly one physical screen pixel, is the way to do it now.

The "switch" to get the preview fully rendered at all times actually already exists, in the form of the "Cache Level" setting in Preferences. Having cache level = 1 would force a full render of all previews at all times, every pixel number in the file fully calculated. The problem is that it doesn't work, and this is apparently a deliberate decision. If you try to set it to 1, it will jump right back up to a higher setting. A value of 1 will not stick.

The explanation we've always been given is that this would bog down Photoshop and slow down operations. Most likely it would also be an extra drain on disk space and memory usage. While that is no doubt true, I think it could still be the user's informed decision. You could argue that today's hardware should be able to handle this. On the other hand file sizes have generally grown to match. 

In short, I agree in principle that this can be a problem, and theoretically it can be solved. I don't know why they have to chosen to not enable cache levels = 1.