How to batch export image variations?

Software darktable
1

DT 3.8.1 on debian

After I have done my processing, I do the export with the: RL output sharpen.

The problem is it’s done after the resizing and it also depends on the image, I can’t preview, this means that I have to try one sigma at a time.

Can I do that at the command line, specifying the sigma for different raduises?

or

can I do it with gmic with different reduces (I have looked at the https://gmic.eu/reference/gmic_reference.pdf and can’t find rl sharpening)

Thanks

2

I’d look at the Diffuse or Sharpen preset for sharpening, either AA or non-AA. I’ve found this completely removes the need for post sharpening.

3

I did and I disagree, it’s very much a matter of image/subject. For photos of dog, it makes a big difference.

Screenshot_2022-02-19_17-35-51
Screenshot_2022-02-19_17-35-512556×1051 3.49 MB

  1. resized to 1500px by dt
  2. view in geeqie
  3. left: sharpen/diffuse dehaze + sharpen demosaicing aa
  4. right: sharpen/diffuse dehaze + sharpen demosaicing aa + output sharpening.

When resized to 725px wide, the difference is even greater.

Thanks

4

Do you use high quality resampling in export? What are your interpolation settings? Did you enable any setting that may impair quality?

5

How many output sizes do you use?

Iirc, output sharpening is used to correct for the loss in perceived sharpness due to the down-sampling, and is not dependant on image content. So for a given camera and output size, the required sharpening should be constant.

That suggests you could define presets for your output sharpening and your export sizes.

6

Here are my settings:

  • high quality resampling: yes
  • interpolation: I don’t know, which one is it?

here’s my print screen

Screenshot_2022-02-20_11-18-37

Thanks

7

I usually use 1 down sampling size: 725x725. That’s 80% to 90% of the time. Then I occasionally use 1500x1500 and 2500x2500 or full size (0x0).

A preset would seem like a very good idea. Thanks

8

If you didn’t change it, it’s still probably the recommended default.
The interpolators can be adjusted in the preferences.
https://docs.darktable.org/usermanual/3.8/en/preferences-settings/processing/

9

It’s set to the default: lanczos3, but in the docs it says:

pixel interpolator (scaling)
lanczos3 can cause pixel overshoots leading to artefacts but sometimes gives a more crisp visual appearance. This option is therefore only provided for transforming (scaling) algorithms and is the default value.

It looks like the output sharpening richardson-lucie does give me the “crispiness”, short of crunching, then should I change the interpolator?

Thanks

10

If you don’t see artefacts, then there’s no reason to change it, I think.

11

Thank for taking the time to explain.