I was working on the great horned owl (Great Horned Owl with the moon) when I noticed a mask behavior which surprised me. I like to understand better why.
I modified the original photo by removing the moon via retouch and cropped to isolate the owl. Next, I focused on the owl by masking the animal using a parametric mask in the exposure module. For that the grey sliders, which resulted in a nice mask containing the bird and the branch of the tree it sits on. So far so good, but after switching off the display mask option I saw a bright edge around the bird and the branch. Its origin is no doubt related to the sharp edges between bird / branch and the background: moving the details threshold to the right delivered a mask only containing (sharp) edges.
I used other blending modes and found that multiply, divide, subtract and chromaticity made the bright edge disappear. The bird however turned nearly black instead of brighter, which was my intention.
I am well aware of all kind of purple or colored chromatic aberrations. The forum has numerous references to that issue. So tried the chromatic aberration module, but no improvement. Neither after rawchromatic aberration or the deprecated defringe module. Switching on the high quality processing to see whether it was a preview issue did not change anything.
In the end I saved the day by increasing the feathering of the mask significantly and found the halo around the bird quite satisfactory. It now stands out.
However, I like to understand was it happening here.
I attach the xmp file. I am on Windows 11 and Darktable 4.8.1
maybe use hue for masking - hover over the slider bar and press c key to see, if one of the parameters is better to separate the background: 2024_08_12_0457.ARW.xmp (12.2 KB)
The feathering slider is particularly important when the subject is a bird.
@Pieter_Zanen
No… Seriously… my subjects are people and I find this technique really useful. You can use it with drawn or parametric masks. I used to be afraid of masks and having to spend hours drawing accurately: darktable makes it easy. You can even duplicate the instance, reverse the mask on the new instance, and use that to make a different adjustment to the rest of the picture. All without lines, patchy bit, halos etc. Thanks to feathering.
This isn’t necessarily a great mask (in my edit here) maybe but its one quick way to do it…
Just one note too…your jpg above is 13 mb…we generally try to keep them down in size to 2 or 3 mb or even less. You can drop the quality and/or downscale it… People can get the details from the side car for a high quality full size jpg…
many thanks to all for their answers and proposal how to avoid / solve the problem. However, I still do not understand how the masking caused the bright pixels to appear. I feel the question stands
The masking wasn’t that precise, that you separeted the owl only. And I think without the feathering tool it isn’t possible at all to separate the owl from the background really reliable. That’s because the edges are usually somewhat melting with the background.
So why are now the edges bright? Simply because you made not only the owl brighter, but small parts of the background as well.
Your mask had a super sharp transition. You chose a parametric mask and you were not really able to feather with that using the feathering triangles because the selection critera (range) on that channel to capture the bird was tight… You can see from a simple application of your exposure bump which was almost 3EV that any area of the sky would become quite bright.
Any time you create a harsh transition in tone you can risk a halo or artifact so you have to be able to find a way to feather it to ease the transition… on a featureless background this can also be a challenge…
Using a combination of parametric channels, with perhaps a drawn mask and getting the right blend of the mask adjustment parameters, ie the feathering, opacity(mask not module) blur and contrast… usually you can land on a good fit… Sometimes it can be easier to mask the simple thing like the solid background and then invert it to give you the bird… there can be many strategies…
I thought everyone would be groaning because it was such an obvious pun it must be an old joke!
For passing beginners (I’m not much more) the feathering slider and the adjustable feathering dotted line around the mask are two different things but, of course, they can be used together.
I loaded your xmp file and I could not through feathering or any other means get a good parametric mask with your edit. So I started from scratch. First I decided DT would find it easier to do a parametric mask on the blue sky rather than the owl. So I did that and inverted it. But before all of this I denoised the image so a clean mask could be made.
Importantly I created a second instance of exposure to do the masking where you tried doing all the heavy lifting with a single instance of exposure. I also applied feathering to the mask. I used less exposure lift on my edit as if you go too heavy handed with any single module you are more likely to get artefacts.
I used the shadow and highlights module and the color balance rgb module to do further lifting of exposure on the owl. So I shared the work load between three modules to reduce the risk of artefacts.
I feel the main reasons you got a poor result was only using a single instance of exposure module rather than a combination of modules and denoising from the start is important.
I hope my xmp file helps you. Thanks for your interesting question here on the forum. I find the challenges helpful to improve my own skills.
Many, many thanks to all for their efforts to cope with the issue I raised. It is much clearer for me now what happened when I masked the bird with the parametric mask, grey slider. The fact that the mask did not perfectly match the bird / branch caused the bright edge: that mismatch did go unnoticed by me (hard to detect).
Indeed the use of one single instance of exposure had its issues: the spot of bright feathers under the left eye of the owl needed additional work.
For me the take home message is to close very close to masks and bear in mind that sometimes you need more than one module to handle issues
Or use a (rough) drawn mask, use feathering (the slider), adjust the mask opacity and contrast. Drawn masks can be combined with parameters, too. I find drawn masks often easier to use.
I may, for instance, be coping with an over-bright dress. I will use parametric masking if it is fairly flat colour: first colour, then chroma, brightness, grey to narrow it down. Then, if other parts of the pic are affected, adding a drawn mask around the dress limits it. It can often be drawn quick-and-rough, just so long as does not extend over areas I don’t want affected. Sometimes use a drawn mask and negate it if there is one patch I need not affected.
I’m not a deep and learned user of darktable. And I’m not a photographer that [can] spends hours on crafting a single picture. I’m working to get through a batch of 50-100 pics as quickly as I can whilst giving care to each. And darktable masking fits this workflow: it can be quick and relatively easy. And, again, I’m posting this for the relative newcomers who may find it hard to believe that this stuff can be simple.
(I photograph classical-Indian-music concerts. I guess it’s being an event photographer except I am entirely amateur, although I do provide my pics to the musicians and organisers.)
