Normalize image color spaces before comparison

[ejensen]

Overview

Use the sRGB converted snapshot when doing the perceptual comparison. This reduces the chances of failures when comparing snapshots using different color spaces.

This colorspace normalization technique was originally introduced in #446 and this PR extends it to both the reference and new images when performing perceptual image comparison.

Unit tests were added to verify that images in the P3 and sRGB colors spaces match after colorspace normalization.

Related Issues

• Snapshot taken on CI has slight color differences compared to local #313 (comment)

[pilot34]

Hey. Should we merge this PR after the rebase? Looks like it was approved, but never merged

[Kaspik]

@stephencelis Please, is there a plan to merge this?

[ogiba]

@stephencelis I will bump this topic cause there was no answer from few months

Could you provide information what is blocking you from merging it into the main branch?

It will be nice feature/fix that could reduce lots of issues.

Thanks!

[brucerune]

+1 please merge :)

[adarhef]

After a while I figured out the difference between my CI machine and the dev machine was the color space, running on macOS.
Right now I simply normalize the NSWindow used for comparison by setting its color space to sRGB in my snapshotting strategy.
I imagine it won't be necessary if this PR is merged, but I imagine it might not be merged.
While users not understanding failures are due to color space differences is problematic (like just happened to me), I can imagine users might be surprised if images look different in the screenshots they take compared with what the interface looks like when just running on their dev machine.
It might be better to inform people about color space normalization so they can be intentional with their color space choice.
Just a thought