Hi grimf
Unfortunately, you have a problem that became intermittent and which you cannot reproduce as mentioned in post #6. When I loaded up your PSD file I could not repeat what you saw in Photoshop. In fact, what I could see on my screen was exactly what you were seeing for the darker toned image.
Without being able to reproduce the issue you saw by either of us, we would be just guessing on what might have changed.
What this means to me is that the present PSD file that you see is displaying correctly with the darker tones for what is in that PSD file. I did view it at 100% with a stamped Layer to make sure I did not have dsplay anomalies. That may not be what you want yet I believe it is being properly represented as darker tones. So something changed and it is not clear if it was some minor change made in your image/layers or something slightly changed in the software, display magnification etc. If you have an older version of the PSD file you might be able to find the difference between the two PSD files (if there was a change).
Trying to fix the issue you saw without root cause could very well be just sending you down a "wild goose chase." Lots of energy spent and not much to show for it.
Not that when I viewed your image at the magnification from your first image (15.13% as show in lower left corner of PSD screen), I was able to reproduce some tone differences between your existing file and one that had a stamped Layer yet it was not as dramatic as what you saw.
Note that even without having your display calibrated, if your image is in a known color space (yours was and sRGB), and you export to the same color space, and have the profile embedded, and use an image viewer that is also color managed, the images will both look the same between Photoshop and your alternate viewer (e.g. color managned browser). Now without color management, what you see may not match a color calibrated/profiled monitor yet you you would not see differences upon export.
That is why I think tryign to solve this with color calibration/profiling would not solve whatever issue you had. Calibrating/profiling would be good in general yet I believe not solve the root cause issue of what you saw.
You would need to be able to consistently repeat the problem so others could give it a look to make good progress.
To answer your specific questions, your image was already in sRGB so having the box set to sRGB is good for internet viewing yet would not cause any changes to the image. That by itself does not embed the color profile with the image. I don't know the version of PS you are using yet most versions have a box labeled "Embed Color Profile" which also would need to be checked. As far as future types of monitors, yes they are getting better about being set or have a mode that can be set to represent sRGB or Adobe RGB color space. You still would have the issue of making sure the monitor On Screen Display controls are set correctly and everything still depends on the brightness of the monitor as well. All monitors will age with time and not keep that perfect initial calibration/profiling over time. Without knowing root cause of your problem, it is hard to know if this was a color management issue or not.
If I were you and still wanted to fix the problem, I would try and get the problem to be repeat reliably without being intermittent. If you need to move on, you may need to correct your image to the desired tone and move on. Not the best place to be in yet that is my assesment.
Hope that is helpful
John Wheeler
It's subtle but the exported version is darker and more jagged.
