Solution to 4k/5k iMac crippling slow downs on MacOS

Hello Everyone.

I honestly have been wanting to use Rawtherapee forever. Partly because the software is really amazing and it fits a workflow that I have wanted to do where I do the raw adjustments in RT and then move to Gimp for the rest of the “localized and intrusive” adjustments.

By the time I realized I wanted to use RT I already switched to Mac and the software became literally unusably slow. From my research it seemed like RT could not handle the 4K res with the particular hardware choices of apple.

Resolution is the issue. First and foremost like the devs have stated more pixels = more processing time. I tried numerous times to lower the res of the screen but nothing would work.

Ok enough talking turns out lowering screen resolution on a 4k retina iMac only scales the display so you are still technically 4k just “zoomed in”.

I stumbled on a trick where if you are in the Display settings hold the option key and click the scaled radio button you get a list of resolutions. Below the list is a check box “show low resolutions”. click that and every setting of display resolution now has a non 4k version marked (low resolution). Pick one of those and you can still keep your high display size but leave the realm of 4k and boom RawTherapee is snappy and amazing.

Can you post a screenshot at 100%, please?

@TooWaBoo not sure what you mean by screenshot at 100% but here is a screenshot of the settings after doing the above to achieve solid performance in RT.

My fault, I meant a screenshot of RT to see if everything looks like expected.
Did you test the Pseudo HiDPI-Support in the preferences of RT too?

Could very well be a bug, because on Linux and 4k I didn’t notice any slow down going from 1080p to 4k with RT. At least not in the noticable range.

@K-1 it very well could be a bug somewhere. Through my research the devs can’t seem to find one so it is assumed for some reason on MacOS having 4x the pixels to work on performance may tank much harder then on Linux or Windows. Could very possibly just be a Mac thing who knows. This seems to be a workaround that works. Until I found this little hidden feature RT was completely unusable on my machine.

@TooWaBoo here are some screenshots of RT. The first is without the HDPI turned on the second is with it Turned on both look identical to me. The real take away for me is under neither mode is the UI too big everything looks the same as if I never changed to a low resolution mode.

Thanks, looks good. I don’t know if you know that with HDPI on, the GUI change its size with font size within RT.
The screenshots are not identical. Check the button and icon size.