ART processes images 3-4 times slower than RawTherapee for some reason

I don’t know why but ART is perfoming about 3-4 times slower on the same computer than RawTherapee. What I mean by that is, for example, when choosing an ARW image from the bar it takes about 4.5 (!) seconds to load it. So, the image area turns black and I have to wait all that time until all the progress bars below the image will fill. That also applies to magnification: when I zoom into an image, it has to become “unpixelized” and it takes about a second, which is a lot when you constantly zoom in and out. In RawTherapee, loading a raw image takes about 1.5 seconds and unpixelizing takes almost no time.

I checked the settings but could not find much difference in processing methods. And if I could, I changed them and it didn’t affect processing times. So what could be the reason for this?

EDIT: I should’ve clarified that I’m using Windows 10.

Someone might share your experience from this group but maybe post an issue over on @agriggio Alberto’s bitbucket site to assist any investigation into the problem?? agriggio / ART / issues — Bitbucket

Welcome by the way…

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Are you on windows? If yes, the culprit might be exiftool. You can try renaming exiftool.exe in the ART installation dir to something else like exiftool.exe.old and see if that helps. If yes, I will try to understand why it happens. Running exiftool is generally slower on windows, but I have seen reports that in some cases it is significantly slower…


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I can basically confirm everything minir36957 wrote, even though it doesn’t particularly bother me. And it’s Windows only, on Tumbleweed the described actions are a lot faster.

Demonstration of the zoom thing, RT compared to ART:

The main problem seems to be noise reduction for Windows. On Tumbleweed the same photo with same settings is as fast as RT in this video. The real slowness starts at zoom 1:1, when NR really kicks in.


Thanks for the demo. I’ll see if I can add some caching to make this faster. As I don’t use windows myself, I never noticed it…

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This change (using built-in exiv2 rather than external exiftool) made a huge difference in the File Browser responsiveness for me.

The only other thing I’ve noticed (although TBH I’ve not explicitly looked) is the Spot Removal tool in ART seems to be a bit more sluggish and jerky than in RT. But that’s difficult to quantify to any real degree, what with OS caching, etc. But it seems a bit snappier in RT.

I don’t have a high-end machine, although it’s not old either. Neither ART, darktable, RT, GIMP nor Affinity Photo just fly on it. However, none of them are laggy to the point of interference. I’ve disabled OpenCL for Affinity Photo due to what I suspect is a buggy driver, but that’s neither here nor there with RT and ART since they don’t use the GPU.

That’s not too far from my experience as well. I have an 8-core AMD Ryzen 5600 series laptop with 16 GB RAM (and a cheesy little GPU, FWIW, but not a factor here). I find that on my machine turning Noise Reduction, Sharpening and other intensive tools on really impacts things. So I try / set NR, then disable it until I’m ready to pull the trigger.

I’ve just updated to the latest ART on Windows, and it can confirm that on 100% zoom it works noticeably slower than it was previously - same behavior as in apostel338 video, slow “unpixelizing”. It is noticeable with NR both ON and OFF (though with ON it’s even slower of course).

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What is “previously” exactly in this case? What version?


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I couldn’t find which exact version I had before updating. I’ve just tried some older versions (1.5 month old) and I don’t see any difference anymore :person_facepalming: :smile: They are all equally slowish, though nothing critical on my new Ryzen 7950x (which is extremely fast CPU). I apologize for the confusion and noise.

One thing I noticed though, is that with NR ON when I scroll by dragging a rectangle on Navigator - it always “unpixelizes” fast. But when I scroll normally (by dragging main image) - it is slowish sometimes (when I drag farther?).

Thanks. I’ll try to investigate

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Yes ART is sometimes slow. When zooming, you have to wait, the noise module activated to process a fairly noisy image, it’s very slow when reloading. I have a computer with Intel core I7 and 8Gb DDR3 memory. It doesn’t bother me, I have time, but it’s very slightly annoying.
Oui ART est parfois lent. En zoomant il faut attendre, le module bruit activé pour traiter une image assez bruitée, c’est très lent au rechargement. J’ai un ordinateur avec Intel core I7 et 8Gb DDR3 en mémoire. Ca ne me gêne pas j’ai du temps mais c’est très légèrement agaçant.

I also confirm on Kubuntu. RT is faster with the active noise module. Never noticed before but I only use ART
Regards. Roberto

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Renaming the file indeed made some difference. Are there drawbacks from doing that?

Just to clarify: the pipeline of art has become quite different from that of RT, so in general performance differences might be normal. Also the denoise module has been reworked btw. However I’ll try to see if things can be improved.


Well yes, you lose lens corrections embedded in the metadata. I think recent versions of exiv2 support this too, so I might look into that

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Hi all,
can you try this version and see if it improves things a little bit? Do not expect miracles, but I tried to remove some bottlenecks… (Just unzip and run, no installation needed)

No difference for me.

No difference for me as well. I tested in both automatic and manual NR modes. Automatic is still noticeably slower when zooming in (I use manual and it doesn’t bother me).

Ok, thanks. I expect at least some speedup in exporting, as I enabled the fast float plugin of lcms which is significantly more efficient than plain lcms. I didn’t do anything for denoise, it’s just the way it is right now. I tried to change the logic for triggering the automatic chroma denoise recomputation, so it should happen less often, but when needed it will be the same speed as before. I also tried comparing with RT and couldn’t notice any big difference when using similar settings. However, it is true that it’s more and more difficult to use similar settings as the two apps drift away, so it’s a bit hard to compare. Anyway, this is the way it is for now, sorry…