darktable create blur

I am looking to apply a Gaussian blur to a portion of my image in darktable. I can accomplish this using GIMP, but feel that I could be more effective with my particular image by using darktable’s powerful parametric masking. I’ve searched this forum, searched online, opened the user manual and performed a search (Gaussian can be found, but it is used to describe the behavior of sharpening modules.

The solution is probably staring me in the face, but I’m hoping to facilitate my search for a solution by posting here.

Suggestions appreciated.



The low pass filter can soften and you can chose the method including “gaussian” blur (default).


You can also try the soften module.


Thanks for the replies. I am trying out all suggestions.

I would rather use the equalizer. It works on a Parametric Mask and has granular adjustments.

So, I’m trying to work with the equalizer. When I select parametric and drawn as the mask, I could adjust the parametric to where I wanted it, then, I wanted to use the paint brush to draw a mask which for which I wanted to assign the same polarity. But, when I finished the painted shape, the yellow mask only appeared on the painted mask, the parametric yellow disappeared. Assuming that this was to do with my setting for combining masks, I tried the other settings.
Now, I’ve gotten myself into a situation where, no matter what I do, I either have 100% yellow mask coverage that no longer responds to the sliders, or, if I switch polarity, all yellow disappears.

I am probably being dense, but I have read and watched tutorials, and, now, I am asking for assistance here.

I have a photo of my Standard Poodle, and, just for fun, wanted to isolate her against a brick background. Until you helped me in this thread, I had not found how to even create a blur (thanks, I’m over that hurdle). Now, I’m looking to complete my objective in isolating my puppy so that I can apply a blur to the background.

I’ve looked at some intriguing Gimp tutorials, and have followed one step by step, but, if I could learn to do this with darktable’s powerful masking, I’m guessing I could get the whole process down to a few steps.

I really appreciate your helpful comments. Any other tips you can offer would be appreciated.

Thanks so much.


Ok, so, I closed darktable, then deleted the xmp file for that image and started again. The parametric and drawn masks are now working the way I want them to, but I am curious if there is a way to have polarity assigned to individual drawn masks. I have my puppy 70% isolated using a combination of drawn and parametric masks (drawn masks set to negative polarity). But, part of her is not “covered” in the yellow from the parametric mask. If it were possible (or if I knew how), the simplest solution would be to draw a mask with positive polarity to finish masking her. If I select an individual mask, clicking the polarity button switches the polarity of all masks. If I increased the selected area with the parametric tool, so much of the background area will be masked that to then excluded the additional background areas by drawing additional masks with negative polarity would involve such detailed drawing as to defeat the justification for masking all together.

Perhaps what I’m looking to do cannot be done. I don’t know if I can reverse blur effects in a second instance of the equalizer tool if I applied some blurring that included part of my subject in this instance.

Thanks for any help.


That can not be done. By blurring you loose Information that you can not restore. Some algorithmus or even the use of artificial intelligence might make a “good guess” but that will not be the same as the original. But darktable allows you to go back to each step. Make your mask more precise. Gimp might be better suited for this kind of work.

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Thanks for the reply. I didn’t think it could be done. I am spending the morning working through this. I have the manual open as I type. I’ve worked through one GIMP tutorial where the subject with flying hair is nicely isolated from the background, but it involves many steps, and still, one is left with a blank background, so there is yet more work to do.

I’ve gotten very close on a couple of images, and am working through the manual. The manual speaks of setting polarity for “each” mask, but I am not certain if each refers to THE parametric mask and THE group of shapes that make up the drawn masks. So far, I’ve not discovered a way to assign polarity to individual masks. Perhaps there is a way to group masks. I’m checking the manual, although I know there are plenty of experts here (which may include you, LOL), so, hopefully, I’ll be able to figure this out with help from this forum.

Thanks again for the reply.


You specifically asked about Darktable. I find background blurring a lot easier in Gimp. I use a threshold mask to isolate the subject. Grow the subject selection by a few pixels. Now use a mask to clear or “erase” the subject in order to have a separate layer that is background only. Blur that as needed. Then use the original subject mask a second time–on the blurred background layer–to erase any portions of the blur that might have encroached on subject space. Merge the two layers.

You can make any image look like an image made with a telephoto at F1.4. I find Gimp background blurring useful for extreme macro work too. In that context the background will be blurred already anyway. But further blurring often accentuates the sharp focused subject, particularly so in focus stacks, where you can have the entire subject sharp as a tack, and the background almost homogeneously blurred.

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The retouch module also has a blur function. IMHO it is well suited for smoothing skin.


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Old thread but it’s up my alley. I use bokeh a lot for wildlife shots. I’ve worked hard on bokeh in Dartable but find it not only more convenient in Gimp but more powerful too, largely because you can grow and shrink the masks by a few pixels and then apply the subject mask to the blurred background after the blurring.
That may be possible in the latest darktable, with the masks menus, but it is a bit combersome.

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