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I am using Darktable 3.2.1 and I can't get it to use the JPGs embedded in RAW files for preview within Lighttable. There is an option named don't use embedded preview JPG but half-size raw in the preferences but it doesn't have any effect. Whether it's checked or not, Darktable always generates previews by processing the RAW file, which is very slow. This issue has made Darktable quite unusable. Is there any way to fix it?

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  • let me give you some tips for the time being. you can try taking RAW+Basic small jpeg setting in camera then setting the darktable to use them for previews instead... Also maybe its your slow storage coupled with high cpu and ram usage. Slow hdd. Usb over camera/slower card Reader or just very slow sd card? Try doing some speed tests and monitor your CPU/RAM usage by using the task manager. Worst case being your other programs (antivirus etc) using the hdd so you should try monitor ing hdd usage too. – Delta Oscar Uniform Dec 7 '20 at 16:03
  • Thanks. I don't know how to set Darktable to use JPG previews, the relevant option is being ignored as explained in my Q. I don't think it's the disk as the preview is slow only the first time I look at the photo. Afterwards preview is near instantaneous. – Grzegorz Chrupała Dec 9 '20 at 13:18
  • from the same menu select light table (its between import and dark room) and check high quality thumb processing to small then go to cpu gpu memory and try to fiddle with disable backends. İncrease memory a little bit for thumb nail cache then try enabling opencl support. After closing the program try finding these cache files then delete them. It might have a problem avout color management too which will lengten the process. – Delta Oscar Uniform Dec 9 '20 at 13:37
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    i actually thought about an stopgap solutions. Yoy can try getting irfanview (dont forhet to install plugins too) then use the thumb nail viewer that comes with it. It has option to select what program to open files with. If you cant then there is also windows camera codec pack that lets you see the thumb nails. İf you are on Linux you can try finding. Thumbnail browser or if you are in Gnome desktop (which wastes lots of ram but whatever) sudo apt-get install gnome-raw-thumbnailer ufraw-batch to see the thumb nails in Ubuntu – Delta Oscar Uniform Dec 11 '20 at 11:43
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    well you can try moving them to a different directory to clean the clutter at least which should work good with the camera codec pack or the Gnome pack i mentioned. – Delta Oscar Uniform Dec 12 '20 at 10:51
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The whole point of a raw editor is to process the raw data, not the embedded pre-processed JPEG data. Darktable only uses the embedded JPEG-data for the very initial preview, which you can see directly after importing as thumbnail in the lighttable (but that also takes some resources, although minor). After processing, including just opening the picture in the darkroom mode, the processed RAW data is used as thumbnail.

If darktable is slow for you, I recommend you get faster hardware, either CPUs or GPUs (latter is recommended). Just using the embedded JPEG-data for thumbnails won't make your experience with darktable or any other raw-data processing programm faster.

For more details on how darktable handles thumbnail creation, please refer to the manual section 2.2.3.1. Thumbnail creation:

[...]

When darktable imports an image for the first time, there are two possible sources from where to take a thumbnail. darktable can either try to extract an embedded thumbnail out of the input image – most raw files contain these kind of thumbnails generated by the camera – or process the image by itself using default settings. You can define how darktable gets its thumbnails in the GUI preferences dialog (see Section 8.1, “GUI options”).

[...]

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  • I understand the point of a raw editor. I'm talking about the preview. Darktable takes about 3 seconds per photo to show a preview of it because it generates it by processing the RAW instead of displaying the embedded JPG. This makes it very difficult to sift through a few thousand photos to quickly mark the ones I want to process. – Grzegorz Chrupała Dec 6 '20 at 19:23
  • Thanks for the edit to your answer, but the problem is that this GUI option doesn't work, as I mentioned on my question. It is possibly being overridden by some other option, or it's ignored under some circumstances. I need help with this specific problem, not generic advice. – Grzegorz Chrupała Dec 6 '20 at 20:06
  • That's hard to debug from remote. My first question would be if the RAW file actually contains a JPEG and how you determine if darktable does not the way you expect it. – sebix Dec 6 '20 at 20:24
  • The RAW files do contain JPG preview as I can extract them from the RAW using a Python library for example. I don't know for sure what DT is doing, but I have two reasons to think it's not using the JPGs: (1) it takes ~3 seconds to visualize a photo when accessing the preview for the first time with the W shortcut in lighttable (2) the preview does not look like the extracted JPG, but like the photo processed using DT default RAW processing parameters. – Grzegorz Chrupała Dec 6 '20 at 20:49

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