channelmixerrgb: change the saturation control

[aurelienpierre]

introduces an alternative cross-talk saturation change that behaves more predictably

bump the legacy params and handle conversion

remove GUI RGB params swapping for the v1 and handle it in commit_params()

[kofa73]

Erm, I need a bit of git help?
Both gh pr checkout 7839 and git fetch origin pull/7839/head:channelmixerrgb-fix-rgb fail with

! [rejected]            refs/pull/7839/head -> channelmixerrgb-fix-rgb  (non-fast-forward)

I've never seen this message in my years of using git daily. According to cli/cli#562, this can happen after a force-push, which we never allow on our repos.

[matt-maguire]

Just fetch it onto a branch with a different name, eg.:

git fetch origin pull/7839/head:channelmixerrgb-fix-rgb-v2
git checkout channelmixerrgb-fix-rgb-v2

[TurboGit]

Code looks good, not tested yet.

[TurboGit]

All good, ready for merging.

[dterrahe]

Just so I am sure I understand the purpose here:
The old conversion method needs to be supported (and even be selectable) because some people may have grown to prefer it? Or because the same results for an old saved version cannot be achieved with a one-off conversion in legacy_params? I haven't followed the whole discussion around this issue, but I thought it was just a bug and that getting the same results for existing images could be done once so it would look the same. Do we all agree that for new users (who've never been exposed to the initial version) having comboboxes with versions in many modules doesn't add value but does add confusion? Unless there's really an advantage to the old algorithm in some cases (which ideally would then be explained somehow).

[aurelienpierre]

The 2 versions need to be supported because they look very different and edits will be lost. The pixel code is actually different, it's not just a matter of massaging user params. Both versions are in-house R&D so there is no reference implementation or anything that could be used as ground-truth.

The combobox is mostly there to allow migrating old edits to new version while retaining the rest of the parameters.

[TurboGit]

Works for me. Thanks!