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P: Different histograms for identical copies of a raw file

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LEGEND ,
Jun 06, 2019 Jun 06, 2019

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Develop displays histograms for identical images with small but noticeable differences, and these differences depend on the order in which you edit the files.  By itself, this probably doesn't have any impact on users, but it may indicate a worrisome underlying bug in how Develop caches computations.

See this screen recording, and follow these steps precisely:

1. Download this sample raw into a folder and make a copy of the raw in the same folder. Rename the two raws A and B.

2. In LR, do Preferences > Performance > Camera Raw Cache Settings > Purge Cache. 

3. Restart LR.

4. Import A and B.

5. In Library, select A and make a virtual copy.

6. In Library, select A and Cmd-click B (order is important).

7. Go to Develop, and use the cursor keys to switch between A and B.  The histograms appear identical.

8. Go to Library.

9. Without changing the selection, go to Develop, and use the cursor keys to switch between A and B.  The histograms now have small but noticeable differences.

10. In Library, select A and Cmd-click the virtual copy (order is important).

11. Go to Develop, and use the cursor keys to switch between A and the virtual copy.  The histograms have small but noticeable differences.  

Tested on LR 8.3.1 / Mac OS 10.14.5.

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9 Comments
Adobe Employee ,
Jun 06, 2019 Jun 06, 2019

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Hi John,

It looks like the download link to your sample bug file has expired. Can you please repost it? I have yet to be able to reproduce the issue using various RAFs.

Thanks,
Kelly

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LEGEND ,
Jun 06, 2019 Jun 06, 2019

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Adobe Employee ,
Jun 06, 2019 Jun 06, 2019

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Got it, thanks.

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Adobe Employee ,
Jun 06, 2019 Jun 06, 2019

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Thanks John. I can repro with that test file. I'll get it filed in our bug base and have a dev look into it.

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Adobe Employee ,
Jun 06, 2019 Jun 06, 2019

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It looks like what is happening here is that Lr is showing the Histogram for the interim preview when switching from A to B, but is not updating (as it should) once the full negative loads. I don't expect any issue beyond the Histogram UI not updating properly in this case, and it should be an easy fix. Thanks for reporting it John.

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Adobe Community Professional ,
Jun 07, 2019 Jun 07, 2019

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Kelly C., I can see the same issue in LR 8.3.1 with DNG Export files. It's very simple to duplicate. Reset a raw file (default settings applied), export it to DNG file format, and you expect to see the same histogram as the original raw file. The Library module histograms are identical, but not the Develop module histogram.

1.    If you apply any Develop setting to the DNG file and then set it back to 0 the histograms match.
2.    They will also match if you simply click on the reset button with the DNG file selected.
3.    Zooming to 1:1 view in the Develop module the histograms remain different.
4.    Zooming to 1:1 view in the Library module and back the histograms then match at all Zoom views.

I tested LR 8.2 with the Export module set to Compatibility Camera Raw 11.2 and later (i.e. matching versions) and it exhibits the same issue. I also tested LR 5.7.1 and it does NOT exhibit this issue.

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Adobe Employee ,
Jun 16, 2020 Jun 16, 2020

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Version 9.3, an update to Lightroom Classic, went live on June 15, 2020 and contains a fix for this issue. Please install the update and respond back if it does not cure the issue for you. Thank you for your patience!
Rikk Flohr - Customer Advocacy: Adobe Photography Products

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LEGEND ,
Jun 16, 2020 Jun 16, 2020

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Following the bug recipe, I still see small differences in the histograms of the two copies A and B. Here's a screen recording flipping between screenshots of the two histograms:

Image is not available

https://www.dropbox.com/s/4hzrgoxdlgqm8mf/histogram-diff.2020.06.16.mov?dl=0

Here's a Photoshop difference of screenshots of the two histograms (click to see it larger):


I don't think this has any practical impact on users -- as a developer, I'd just worry that this is symptomatic of a more serious bug in how Develop or ACR caches computations.

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Adobe Community Professional ,
Jun 17, 2020 Jun 17, 2020

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The similar Develop module histogram issue I outlined concerning export DNG files appears to be fixed on my Windows 10 system using LR Classic 9.3.

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