Identify dust spots

Software darktable
1

DT 3.0.2

Is there someway of showing dust spots in DT? Before I make a big print, I want to make sure that there’s no dust spot.

I played around with some of the blending modes high pass and differences but no success (most likely due to my limited understanding).

Could somebody point me in the right direction or tell me how they do it themselves?

Thanks

2

The retouch module (3.4.4.12) might be helpful, especially the wavelet decompose part of that module.

Bruce Williams made a nice video about this module (the wavelet part starts at around 10:30):

Basically you work with layers (scales) that go from very fine to course and you can more easily identify the problem spots. It isn’t a magic wand so you do need to put the effort in, but I really like the fine-grained functionality.

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3

There is a pull request open for a dust visualisation mode but it’s waiting someone who understands how to (and wants to) code it:

4

You can set a wave in contrast equalizer - this can bring out sensor dust

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5

What kind of wave?

Thanks

6

Thanks,

I’ll watch the video over the weekend. I’ve never used the retouch module, but it looks interesting…

Thanks

7

this kind of wave:

contrastequalizer
contrastequalizer728×640 45.6 KB

you can shift the waves to the right to detect finer and to the left to detect coarser spots

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8

There was a darktable.fr user who made 2 dtStyle to detect dust on the sensor: Suppression des tâches et poussières

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9

Perfecto :smiley:

Thank you to everybody for taking the time. Not only I learned something new, I learn something very useful.

10

Not for DT, but the Sharpening Contrast Threshold mask in RT renders (as a fallout) dust spots as donuts which are very easy to identify :wink: I will post a screenshot and an example raw file later. Maybe some other devs can use that…

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11

Here’s an example raw D700_20150714_6030.NEF (15.3 MB)

And the dust spot donuts:

grafik
grafik1920×1080 433 KB

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12

Here’s a closeup showing the dust spot donut shape in the mask:

grafik
grafik1920×1080 70.1 KB

And now the same crop of original image without the mask (If you look carefully, you can see the dust spot)

grafik
grafik1920×1080 960 KB

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13

Thank you, I will use it in RT.

14

Another method in Darktable is to crank up local contrast to the maximum. Very useful for spotting dirt on the lens as well. After fixing the dust spots with the retouch module you turn off or reset local contrast. This picture was scanned from a paper copy. I tried to clean the picture and the scanner, but could not remove everything.

1996-1997 Aegina 1 - No 5
1996-1997 Aegina 1 - No 51489×1080 283 KB
1996-1997 Aegina 1 - No 5_01
1996-1997 Aegina 1 - No 5_011489×1080 444 KB

15

or just use the retouch tool. set 7 wavelet layer - in layer 3 you can identify the sharper dust speckles in layer 7 the most unsharp speckles. to remove you heal in the rightmost layer they’re visible and then drag the upper slider to left until you’re satisfied
retouch

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16

I just did a test with the dtStyle “Courbe de correction des tâches 01.dtstyle et 02” on https://discuss.pixls.us/uploads/short-url/khPCapOUkWBGwWX7TOC0JVPGBk3.NEF

Capture du 2020-06-06 09-42-23
Capture du 2020-06-06 09-42-231689×997 1.46 MB

Capture du 2020-06-06 09-41-50
Capture du 2020-06-06 09-41-501689×997 1.48 MB

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17

Hi,
what I have been using so far was to use the Highpass module with both sharpness and contrast set to 100%.

I got this from some video or blog post on the internet, but unfortunately do not remember the original source anymore to give proper credit.

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