P: Thick red/blue banding in brightened shadows of Denoised DNGs

[PvlKnn]

I noticed this a few days ago but didn't realize the scale of the issue until I played around with the Exposure values and tested them to the limit.

I've attached two screenshots of the Develop module. The control image is an RAF photo with Exposure boosted to +5. The experiment is a DNG derived from the RAF, with a Denoise amount of 30. The effect manifests at all amounts from 1 to 100. However, the banding is not present in the Enhance Preview window. I have also attached the original Fujifilm RAF from my X-H2s camera (lossless compressed) and an affected DNG with Denoise.

I can't detect this phenomenon in NR conversions before LrC 13.3. 

The significance should be self-evident. The banding artifacts appear in images with lifted shadows or underexposed photos with boosted brightness.

Lightroom Classic version: 13.3.1 [ 202405311538-6d7c0308 ]
License: Creative Cloud
Language setting: en-CA
Operating system: Mac OS 14
Version: 14.5.0 [23F79]
Application architecture: arm64
Logical processor count: 12
Processor speed: NA
SqLite Version: 3.36.0
Power Source: Plugged In, 80%
Built-in memory: 32,768.0 MB
Dedicated GPU memory used by Lightroom: 5,764.7MB / 21,845.3MB (26%)
Real memory available to Lightroom: 32,768.0 MB
Real memory used by Lightroom: 3,716.8 MB (11.3%)
Virtual memory used by Lightroom: 424,322.1 MB
Memory cache size: 1,238.0MB
Internal Camera Raw version: 16.3.1 [ 1889 ]
Maximum thread count used by Camera Raw: 5
Camera Raw SIMD optimization: SSE2
Camera Raw virtual memory: 2281MB / 16383MB (13%)
Camera Raw real memory: 2285MB / 32768MB (6%)

[PvlKnn]

The problem started with the version 13.3 update. The preceding version is fine.

[Rikk Flohr: Photography]

Greetings all, 

A new update for Adobe Photography Products has been released.  The October (MAX) update contains an update for this issue.  

If you do not see the update in your Creative Cloud Application, you can refresh it by hitting [Ctrl/Cmd]+[Alt/Opt]+[ R ].

Note: It may take up to 24 hours for your update to be available in your Creative Cloud app.

Note: This particular issue is exacerbated by the Apple Neural Engine, which is now disabled in this update. 

Thank you for being so patient.

[John R Ellis]

Confirmed that the LR 14 Denoise doesn't produce the red/blue banding observed with the test photo provided above:

https://community.adobe.com/t5/lightroom-classic-bugs/p-thick-red-blue-banding-in-brightened-shadows...

[riccimar]

yes, the bug it' solved on my side, but denoise on a M1 Pro seem much slower now

[Jao vdL]

>yes, the bug it' solved on my side, but denoise on a M1 Pro seem much slower now

As @RikkaRikka notes above, the problem was that the use of the Apple Neural Engine caused this issue. While faster than using the normal GPU cores it has lower precision if you look at Apple's documentation and it appears that this might be whay caused the artefacts. So with a choise between slightly slower and good quality and a tad faster but nasty artefacts in deep shadows, that is not a hard choice. On my M1 Max it is only slightly slower in 14 than it was in 13. It is basically back to the version before Adobe enabled the neural engine's use.