In my basic understanding, there are several factors that will cause halos.
Lens chromatic aberration can appear in a different color (not pure blue) so reducing blue luminance in HSL does not darken the aberration line of color.
Excessive sharpening can change the luminance of pixels along edges which would be more obvious in B&W.
As an alternative to HSL adjustments you could try a Gradient filter and the Range Mask feature set to 'Color'- hold [Shift] and select several points of sky color to limit the Gradient to the various tones of blue in the sky. Then do the B&W convert.
8 or 14 bit? An 8 bit image (JPG?) will have a smaller range of tone values available so may be more prone to the halos.
I agree with all of your statements but feel that my question was not answered and probably because I did not supply enough information.
I have attached an images (blow-ups) comparing Lightroom vs Silver Effects Pro of a cypress tree against a sky.
In each case the images were processed from a 24mb raw image. The attached picture was captured from a Snip of the XY view in Lightroom.
The photo on the left was developed in LR6 by converting it to black/white and then moving the BLUE slider to the left to darken the sky.
The photo on the right was edited (via LR Edit-in) in Silver Effects Pro and saved back to LR. The development in SEP was different as I simply applied the Red filter to the entire image and controlled the amount of sky darkening to be comparable to the LR rendition.
In addition to the white fringing, you can also see a great deal of noise in the LR image.
BTW, an almost identical effect occurs in Photoshop Elements.
I have not tried the same method in Photoshop but plan to do so but I rather suspect that it will NOT have the same problem.
As regards the gradient filter: It too has similar type problems but not quite as noticeable. And it is a lot more trouble to mask only the sky.
I have been using both LR and SEP for many years and much prefer SEP to LR for B/W conversion. The limitation of SEP is that it only handles 3X8 bit color. The new owners of SEP are working on a 48 bit but that may not be for awhile. Meanwhile I have tried several other software conversion programs andfound that DxO Film Pack 5 does a very good job in converting to B/W. It does so similarly to SEP by simulating various B/W films and filters. It also has a much better grain control than SEP.
Thank you for answering my inquiry.
You have supplied plenty of information, thanks. And I see the problem, and have experienced it, but do not have the exact answer you seek.
There are so many variables when comparing two programs (the image, lens, its color, etc) that a 'technical' correct answer is difficult.
I just applied a similar workflow to my Nikon 24mp image and compared a LR-HSL ( -blue) with the SEP filter (red) and the only difference I can see is very minimal, even at 3:1 zoom.
So keep asking the question, other editing gurus may have the correct answer.
'Select' is the LR image--
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The halos observed are due to chromatic aberration in the image edges. The reason you don't see them in Silver Effects Pro is probably due to applying the red filter, which is the same color as the CA fringing. Try both checking and unchecking 'Remove Chromatic Aberration' in the LR Lens Corrections > Profile panel and see if that reduces it.
You can also use the Range Mask with the Local Adjustment Brush, but you'll need to Export the raw file to TIFF with 'Remove Chromatic Aberration' checked due to a similar bug. Then apply your B&W conversion and other Develop settings to the TIFF file. Hopefully Adobe will correct this, but so far it has not been 'Acknowledged.'
Thanks for the suggestion on using a Range Mask but I am a bit lazy and was trying to do things simply. I have used masks and layers in PS and know from experience that they take a lot of tweaking with refinements to get things right.
As to the Chromatiic Aberations: I tried your suggestions and found only a very slight - almost un-noticable- change as I had expected. The lens that was used to take the photo is exceptionally free from aberrations.
This same halo effect also occurs in Photoshop Elements but does not occur in Photoshop CC when I use the simple Image Adjustments - Black and White - Blue slider.
I suspect that the observed difference iin the image is due to the processing of 8-bit vs 16-bit channels. PSE only processes 8-bit images whereas PS CC, Film Pack 5 and SEP work with 16 bit. My conclusion is that since the LR mage and the PSE image show the same artifacts, that LR also processes in 8 bit.
I may be completely wrong on this and would appreciate any comments.
The differences you're seeing between LR, PS CC, and PSE are probably due to the way you are opening the file. If using LR 'Edit in PS' to open in PS CC you are no longer using a raw file. Try a LR 'Edit in PS' without applying any B&W mix, save the TIFF file in PS, and then apply the B&W mix to the 'Edit in PS' TIFF back inside LR. Any difference?
To help further please Export to DNG the raw file with your adjustments applied that exhibit the issue. Post it to a file sharing site and we can investigate further. Thank you.
There are two types of haloes that cause this problem. One is the already mentioned chromatic aberration. This can be dealt with with the tools in lens corrections. Second is more insidious and impossible to get rid of since it is caused by the way Lightroom generates the color range masks in the luminance sliders. This happens very typically around blue skies when you use the blue slider to darken the sky. You will get 1 pixel bright lines around the edges of objects against the blue sky. Probably Lightroom does not extend the mask for blue far enough. You can't fix this and has been noted many times. If this happens (and it always does with darkening blue skies strongly), the only solution you have is to use different software. I generally use the channel mixer in Photoshop in that case which does not have this issue because it is not based on masking. In some cases, you can use an adjustment brush in Lightroom combined with a luminance mask or color range mask. This works better than the luminance sliders but is not always possible. Auto masking generally creates very ugly haloes and I would not recommend using it for this purpose.
P.S. this has been slightly improved in Lightroom 7.3 with the new profile system. The new black and white profiles there appear to do a better job at this than before. Not perfect but I am seeing fewer of these artifacts.
Jdo vdL and Trshaner,
I truly appreciate your help in answering my question.
As I stated in a previous posting, I tend to be lazy and in a hurry and would like to stay in Lightroom and not have to "Edit In" another program mostly because they all generate a separate (and large) file that I have to include in my Library. These tiff or psd files are sometimes over 100 mb and while my library is smallish, keywording and keeping track of the extra files makes for extra work.
But saying that, I will continue to use PS CC or SEP when necessary. Maybe one day LR will hopefully change for the better.
Once again, thank you both very much.