Darktable troubleshooting cache speed

[vbs (Bojidar Bojkov)]

@priort

Must be frustrating…hope you sort it out. I feel like if you have generated the thumbs then it should be fast…

It is very frustrating - especially when there are thousands of pictures to sort.
I changed the settings to use the RAW file (never the embedded .JPG) but this did not help.

I also found previous discussion how to extract the embedded .jpg

RT: Extracting embedded jpeg from raw image using RT

exiv2 and exiftool are the perfect, lightweight tools for the job: exiv2 -pp my_image.ext to print out the list of recognized previews, and then: exiv2 -ep1 my_image.ext to extract preview no. 1 etc. (or leave out the number to extract them all).

@wpferguson

That’s not correct.

It depends on the size of the embedded preview in the raw file. I’ll use my Canon EOS R7 for an example. The image is 32MP. The raw has 2 embedded previews. One is cache size 3 and the other is cache size 1 (IIRC). So, if I want a HD (cache size 4) or larger full preview, the only way to get it is open the raw file and process the raw data to generate the full size preview.

I am using Sony a7cII (33 MP). Extracting all embedded previews shows 3 of them.
20240518_172005_08011.ARW (35.2 MB)

The 3rd one is actually with very big resolution 7008 × 4672 pixels

That means - for a 2k screen these embedded previews should be more than enough

I have no idea how to explain it but multiple times when I am testing - files that are processed do not appear to re render. Files that are not processed - do re render.