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Lubiano
Lubiano
Participant
August 24, 2026

P: Blue horizontal artifacts appear after applying Lens Blur on Mac mini M4 – Lightroom Classic 15.5 / macOS Tahoe 26.5.2

  • August 24, 2026
  • 7 replies
  • 46 views

Environment

  • Mac mini M4
  • 24 GB unified memory
  • macOS Tahoe 26.5.2
  • Lightroom Classic 15.5
  • Apple Silicon / arm64
  • Lightroom Classic catalog with images using AI masks, Remove and Lens Blur

Problem

Lightroom Classic produces random blue horizontal lines/artifacts on images after AI processing.

The artifacts are variable and may appear only several seconds after selecting the image in Develop. They can also be present in exported JPEG files.

The problem appears to be strongly related to Lens Blur.

Reproducible behavior

I can reproduce the problem with the following sequence:

  1. Open an image containing AI masks and/or Remove edits.
  2. Apply Lens Blur.
  3. Lightroom starts AI processing in the background.
  4. After some time, random blue horizontal artifacts appear in the image.
  5. The artifacts can also appear in exported JPEG files.

The behavior is not simply a display-only problem because the artifacts can be present in the exported JPEG.

Important observations

With Graphics Processor disabled:

  • Lens Blur ON → blue artifacts can still occur.
  • Lens Blur OFF → artifacts disappear after using “Update AI Settings”.
  • Lens Blur OFF + “Update AI Settings” → image becomes clean.
  • Re-enabling Lens Blur → the blue artifacts return.

This makes Lens Blur a highly reproducible trigger.

There is also a GPU-related component:

  • With GPU enabled, the artifacts tend to appear after a delay.
  • With GPU disabled, the problem is much less likely to occur, but Lens Blur can still reproduce it.
  • If a JPEG is exported before the artifacts appear, the exported JPEG can be clean.
  • If the artifacts have already appeared, they can be included in the exported JPEG.

Suspected cause

This appears to be related to Lens Blur's AI/depth processing and/or its interaction with existing AI masks/Remove edits.

GPU/Metal processing may aggravate or accelerate the problem, but disabling the GPU does not completely eliminate the problem when Lens Blur is enabled.

Workaround

The current workaround is:

  1. Disable Lens Blur.
  2. Use “Update AI Settings”.
  3. Verify that the artifacts disappear.
  4. Leave Lens Blur disabled.

Disabling the Graphics Processor also appears to reduce the problem, but does not prevent it when Lens Blur is subsequently enabled.

7 replies

johnrellis
johnrellis
Legend
August 26, 2026

​@Anshul_Saini, ​@Rikk Flohr_Photography, please move to Bugs. I was able to reproduce the problem using the sample photo and settings provided by ​@Lubiano, and I also attached a screen recording showing the precise steps.

Lubiano
LubianoAuthor
Participant
August 26, 2026

Thanks for analyzing the issue and for your support! Today, while reviewing the catalog, I noticed that other photos had the same artifact issue. Yesterday, they didn’t, and they all had Lens Blur enabled...

johnrellis
johnrellis
Legend
August 25, 2026

[View this post in your web browser. It contains formatting and images that don't appear in email.]

 

​@Lubiano, ​@Anshul_Saini using your sample .nef, I was able to reproduce the same artifacts by applying Lens Blur, building a 1:1 preview, doing Update AI Settings, and then building another 1:1 preview.  See the attached screen recording for the exact sequence of steps.

 

The artifacts didn’t always appear, but with the sequence of steps shown in the recording, they usually did.

 

Note in the screen recording that after applying Lens Blur, LR would always use the CPU and GPU heavily for abut 50 seconds, whether or not artifacts eventually resulted. I don’t think this is normal, and it could provide an important clue to the developers. It may be that building a 1:1 preview before this abnormal computation completed is the trigger of the artifacts (i.e. a race condition), but I didn’t explore that.

 

The option Preferences > Performance > Use Graphics Processor was set to Auto (on). LR’s AI commands all ignore that setting and always use the GPU. (Adobe inexplicably refuses to have the AI commands obey that setting, which would make troubleshooting so much easier.)

 

Tested on a Macbook Pro (2023, M2 Max), Mac OS 26.4.1.

Lubiano
LubianoAuthor
Participant
August 25, 2026

Lightroom Classic version: 15.5 [ 202607291506-b8869fa7 ]
License: Creative Cloud
Language setting: en-IT
Operating system: Mac OS 26
Version: 26.5.2 [25F84]
Application architecture: arm64
Logical processor count: 10
Processor speed: NA
SqLite Version: 3.36.0
Adobe GSDK Version: 1.4.0.213

Built-in memory: 24.576,0 MB
Dedicated GPU memory used by Lightroom: 13.006,3MB / 18.186,2MB (71%)
Real memory available to Lightroom: 24.576,0 MB
Real memory used by Lightroom: 2.765,7 MB (11,2%)
Virtual memory used by Lightroom: 445.354,6 MB
Memory cache size: 881,8MB
Internal Camera Raw version: 18.5 [ 2673 ]
Maximum thread count used by Camera Raw: 5
Camera Raw SIMD optimization: SSE2
Camera Raw virtual memory: 6708MB / 12287MB (54%)
Camera Raw real memory: 8059MB / 24576MB (32%)

Cache1: 
Final1- RAM:5.502,0MB, VRAM:9.732,0MB, 2026 06 06 200222 - IT.NEF
NT- RAM:5.502,0MB, VRAM:9.732,0MB, Combined:15.234,0MB

Cache2: 
m:881,8MB, n:95,0MB

U-main: 268,0MB

Standard Preview Size: 5760 pixels
Displays: 1) 5760x3240

Graphics Processor Info: 
Metal: Apple M4
Init State: GPU for Export supported by default
User Preference: GPU for Export enabled
Enable HDR in Library: OFF
GPU for Preview Generation: Off (S5_17)

Application folder: /Applications/Adobe Lightroom Classic
Library Path: /Volumes/Catalogue Work/Lightroom Catalogues/Projects/Matrimonio Venere e Massimo/Matrimonio Venere e Massimo.lrcat
Settings Folder: /Users/lubiano/Library/Application Support/Adobe/Lightroom

Installed Plugins: 
1) AdobeStock
2) Aperture/iPhoto Importer Plug-in
3) Calibrite Camera Calibration
4) Deduplicator
5) DxO PhotoLab 5
6) DxO PhotoLab 5 Importer
7) DxO PureRAW 2
8) DxO PureRAW 2 Importer
9) Find Duplicates 2
10) Flickr
11) HDR Efex Pro 2
12) jf Folder Publisher
13) jf Geocoding Support
14) Luminar 4
15) Photolemur 3
16) Plugin Parameters
17) Teekesselchen
18) TPG LR Backup
19) TPG Metadata Panels

Config.lua flags: 


 

Lubiano
LubianoAuthor
Participant
August 25, 2026

Thanks for the Help! I’m attaching one of the many photos that use Lens Blur. Compared to what I mentioned yesterday, the error is no longer as easily reproducible. LRC generates artifacts that disappear after some time. It’s as if there were a background process that is being executed with a delay. Yesterday, I edited a large number of photos in sequence, whereas today I only edited the photo used in the example.

Anshul_Saini
Community Manager
Anshul_SainiCommunity Manager
Community Manager
August 24, 2026

Hi ​@Lubiano,

Thanks for the very detailed report and for isolating Lens Blur as a repeatable trigger. Johnrellis’ suggestion is the best next step. Could you please provide one affected source image together with its Lightroom Classic settings?

In the Library, select an image that reliably reproduces the problem and choose:

Metadata > Save Metadata to File

Then please share the original RAW file together with its associated XMP/ACR sidecar files.

Before sharing it, please confirm that the same image still reproduces this sequence:

Lens Blur enabled > AI processing completes > blue artifacts appear

and:

Lens Blur disabled > Update AI Settings > artifacts disappear
 

If possible, please also include:

  • One JPEG exported after the blue artifacts have appeared.

  • One clean JPEG exported from the same image after disabling Lens Blur and using Update AI Settings.

  • LrC Help > System Info > Copy and paste the contents here.

  • A short screen recording showing the image initially rendering correctly and the blue lines appearing after the AI/Lens Blur processing completes.

 

If the source files are too large to attach here, upload them to Google Drive, Dropbox, WeTransfer, or a similar service and send me the link via DM.

 

Please keep the affected image/settings as they are for now, rather than resetting preferences or rebuilding the edits. A reproducible sample containing the existing AI masks, Remove edits, and Lens Blur settings will be much more valuable for investigating this.

 

Once we have that sample, we can test the same file/settings on another system and, if reproducible, we will escalate it to the Lightroom Classic product team.

 

Best,
Anshul Saini

johnrellis
johnrellis
Legend
August 24, 2026

If you share a raw photo exhibiting the problem along with its develop settings, we can see if the issue is particular to your LR installation or a more general problem. It will also provide an example for Adobe to work with. 

 

In Library, select the photo and do Metadata > Save Metadata To File. Then attach the raw file and its associated .xmp and .acr sidecar files here. (Each file must be smaller than 47 MB.)

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