Auto Mask in local adjustment brush failed

[dpangelico]

Lightroom Version Number

LR Classic Folder Based Subscription 64

Operating System

1. Windows 10

Lightroom Classic Desktop question: I have used Auto Mask to great success in the past. But I have a series of Blue Hour photos where I thought it should work fine but it does not.

In particular, I zoom in on a building part to select for the adjustment, and the dark blue sky defines the edge of the building part. There is a clearly defined edge. The contrast is pretty good, albeit it is the blue hour, so maybe not so as tonal difference as say daylight. But there is some contrast, and the color is very different (off-white for the building, dark blue for the sky).

I tried

• every slider (even though I think pushing them to 100% is normal)
• turning the auto mask check box off/on/off/on just to see if somehow the software got stuck
• turning on/off GPU
• turned on/off the "show overlay" shading
• restarting

I know this used to work, but these are all DNGs that were created by LR from Nikon RAW doing a three image HDR merge (-2, 0, +2). Could that be complicating the issue?

The edge detection is not working. Any ideas?
Thanks
Dean

 

[Johan Elzenga]

Maybe you should post one of those DNGs in a service like Dropbox and place a link here. Without seeing the images anyones guess is as good your yours.

 

[dpangelico]

Thanks - yes of course. Here is the file
https://www.dropbox.com/s/z98u0p5rtvzhv72/20190726_D50_3506_Grace_Church-HDR.dng?dl=0
More facts:

• Click on the top-most steeple/spire. I use a size ~13 or so brush (not that it matters). Overlap half on the steeple (with selection point solidly on the steeple), half off the right into the dark sky. You get a big bright circle selected; no attention to the edge.
  • Is there just not enough contrast or something?
• The underlying NEF works fine, so it must be a function of the DNG or the HDR processing

Thanks for any feedback
Dean

 

[Johan Elzenga]

Auto Mask works on color differences, and so the problem in this image is that the colors are very similar (there is only a difference in brightness) and the image is rather grainy. Both make it very difficult for auto mask to determine what to keep and what to discard.

Next to that, there seems to be a problem with auto mask and HDR images, at least for some kind of images:
https://feedback.photoshop.com/phot...ent-brush-auto-mask-not-working-on-hdr-images

 

[dpangelico]

Got it - thanks - it uses color differences. I still performed the local adjustments I needed - it was a bit more arduous though, having to be much more careful with the selections

 

[Califdan]

As Johan said, the difference between the steeple and sky is minimal in the original DNG. I believe (someone correct me if I'm wrong) but the auto mask is looking at the original "as imported" image so even if you increase exposure or contrast prior to using the brush, those changes are not seen by Auto Mask. I assum this goes back to the concept in LR that the order you apply changes is not relevant so changing the exposure before using Auto Mask should not be different than changing the exposure of the overall image after applying a local adjustment (I'm guessing here).

Anyway, I increased your exposure by a stop so I could see what I was doing and then used the brush with Auto Mask as you indicated and indeed the mask did not "see" the edge of the steeple (see pink in first screen shot below). I then turned on Range Masking (color) and selected a few sections of the steeple as shown below, but it did not change the mask - it still included the sky.

But I then moved the Range Mask "Amount" slider to the left (all the way to zero) and it now found the edge

Hope that helps

 

[dpangelico]

Nice solution! Thanks very much. Use the Range Mask with discriminator 'Color". I will do that
Excellent
Dean