During the past six month, I have taken quite a few images of industrial architecture. In post-processing these with dt (5.4.1), I arrived at a look that I really like. This includes generous sharpening and local contrast and most importantly a sky that is darkened quite a lot. This pushes some modules quite far, which gives rise to artifacts and halos.
Through trial and error, I stumbled upon a few ways to eliminate these halos, but a recent image has me stumped in this regard. So I would appreciate some input into how this could be dealt with, or if I have just reached the limit of where the raw file can be taken.
First, let me list what I have tried and what worked so far:
Initially, I exclusively used the color equalizer module to darken the sky. When halos showed up, I tried fiddling with some of the sliders but to no avail. But when I turned off the ‘guided filter’ halos went away.
This didn’t wok on every image, so I remembered one of Boris’ videos and I slightly dialed back the brightness change in the color equalizer module and on top of that used the ‘color look up table’ module to selectively darken the sky. Again, this took care of some problematic images
At some point, I also run into sort of noisy, regular patterned artifacts in the sky, but changing the algorithm in the ‘demosaic’ module from 1-pass to 3-pass, resolved that issue
Also, using the ‘color look up table’ module, targeting two different regions in the sky sometimes helped, where I pick a second, lighter region closer to the horizon
When halos/artifacts show up, I activate/deactivate modules to see who is the offender, and without fail it is either the ‘color’ equalizer’ or the ‘color look up table’
So, as mentioned above, I now happened upon an image where nothing of this helps. Below a jpg of the edited image and a 400% crop showing the (just one pixel wide?) halo between the sky and the smoke stack.
Also adding the raw file, if anyone wants to have a closer look (not really suitable for a Play Raw ihmo, as I’m looking for troubleshooting not different interpretations):
If the sky is blue and there is nothing else blue, another possible approach (which works for the image you posted) is to use the “color calibration” module for applying the sky-darkening partially. I.e., to reduce the amount of work for other modules, thus reducing the chances of a halo.
Go to the “brightness” tab and drag the blue slider down. Or even right-click it and enter an absurd value like “-2” and then normalize the channels.
Regarding the original question about the white line, this is likely caused by an imprecise matching of the mask to the original image. Controls like “feathering radius”, “mask opacity”, and “mask contrast” can be used for tuning this down at the cost of some haloing.
A rule of thumb that I use is when when you “push” a module too far you end up with artifacts and you can often go to multiple instances of the module with smaller changes which added together give you the effect without the artifacts.
You can get a pretty good mask from the blue channel and drawing around the 3 area’s of the sky…
Then you will be able to feather and blur and use mask contrast to blend in what ever module…
It looks like the CLUT module is just pushed too hard in your edit… So you can as mentioned target the blue with cc module…
Also consider multiply or subtract blend modes…these can deepen the sky…you will need very little opacity with multiply usually and even less with subtract but they can help as opposed to pushing a module really hard…
I loaded you xmp file and tried to work out when everything went wrong and halos started appearing. The use of the color look up table seemed to be the start of the problem to me. A very sharp line appears along the edge of the chimney etc.
BTW, with your second exposure module you used a drawn mask. I wonder if a gradient mask was not more appropriate for what you were masking here.
I also echo the sentiment about using multiple instances of a module with smaller changes rather than a single sledge hammer use of a module. I also use different modules with similar functions to achieve an effect. So maybe using color look up table in combination with color equalizer and color zones would allow you to select based upon color and to do your darkening of the sky. Each would probably mask the edges slightly differently and this may reduce the obvious halos.
In my example here I have used three instances of the tone equalizer module, each with a parametric mask based on color of the sky. I have applied a little feathering to the mask. The use of multiple instances and feathering has minimised halos while darkening the sky. I believe this is what you were attempting to achieve when you created halos in the color look up table. _T5A8496.RAF.xmp (12.2 KB)
Something to play with if you use a parametric (or drawn and parametric) for sky masking:
Adjust your feather, blur, and the mask opacity found in the “Mask Refinement” section (not the opacity under the Blend Mask section) to deal with those types of halos. Start small on feather and blur (5ish px) and use the opacity to dial it in. If your feather/blur/opacityr is too large, you can get inversions or fatter halos.
Here is an example. I did nothing but add an instance of tone eq. with a parametric mask for the sky just to give you something to play with. I did not concern myself is other artifacts or aspects of the image except the thin halo. View at 100% or with HQ processing enabled. Otherwise it looks crazy
I also got good results with tone equalizer and parametric mask. But to reduce the halos around the smokestacks, I had to either turn off “preserve details” or increase “edges refinement/feathering” in the masking options (or both, or splitting the difference by using one of the “averaged” preserve details options). Though in this case there is no detail to preserve.
Lots of great suggestion here. Thanks, everyone!
I briefly played around with masks before, but didn’t get very far - time to revisit that. Also, read about stacking multiple instances of the same module here before, but that 's one of those things that’s easy to forget - thanks for the reminder.
