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1.1K Points

Sat, Nov 21, 2020 3:37 PM

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Lightroom Classic: How To Prevent Overblown Highlights in Panorama DNGs

I encountered an issue in LR Classic 10.0 with Canon CR3 files produced by Canon EOS R5 camera while stitching panorama with variable exposure (alternatively it might be an issue in processing its own created DNG, not sure here).

Anyway, the original RAW files are without white areas and LR can easily apply a negative exposure to darken everything down.

After creating the DNG this is lost and there are spots that are no longer recoverable.


You can download the original files and the produced panorama here (540 MB in total):
https://www.pastel.cz/temp/lr_overblown_panorama.zip
Curiously, this only happens when stitching ALL FOUR images. Everything is ok if stitching just the rightmost two or three ones.


No art, I was just on a scouting trip :) I didn't care much about exposure etc., but still was surprised that this happened.

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12 days ago

The originals you uploaded don't correspond with the screenshots above?  And they don't correspond with the panorama included in the .zip, and that panorama also doesn't correspond with the screenshots?

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@John_R_Ellis Oops, sorry, correct directory, but zipped incorrect files. It is fixed now, i.e. the archive under the same link is now containing different/correct files.

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21.7K Points

12 days ago

No Adobe raw processing has tools to gauge Exposure, no raw histogram. The current rendering may appear too bright which is not an attribute of exposure per se. Check out Rawdigger if you want to examine exposure of raw data.

https://www.rawdigger.com

Be useful to example each raw individually in that product.

Author “Color Management for Photographers"

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@andrew_rodney Thanks! I didn't mean the original raw files are perfect, but they are handled significantly better in LR. While I am unsure if this is a bug in panorama creation in LR or DNG handling in LR, it seems to be one of these, i.e. a bug in LR.

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37.4K Points

12 days ago

I've seen this happen with cameras that have a built-in neutral density (ND) filter that kicks in when the metered shutter speed is exceeded. The EOS R5 doesn't have one, but are you using the below ND adapter?

https://www.usa.canon.com/internet/portal/us/home/products/details/lenses/ef/mount-adapters/drop-in-filter-mount-adapter-ef-eos-r-with-drop-in-variable-nd-filter-a

(edited)

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Interesting point of view, but no - I was not using an ND filter, so the exposure numbers in EXIF should be directly related to the difference in brightness.

Champion

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12 days ago

First of all, you only uploaded an XMP instead of RAW for 1403 but the 3 remaining photos stitched with the issue you list.  The issue is 1402 is shot at 1/320 of a second and the others are shot at 1/80 of a second.  When creating the pano Lr has to blend the Left side of 1402 with the Right side of 1404 (1403 in your case) and to do so had to overexpose 1402.  Do the pano in Photoshop and you will see how badly the exposures are for this pano and how much blending is needed.  When doing a pano the exposures need to be the same to get a good result or at least closer than what you did.

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@robert_somrak I messed up the upload, sorry. Hopefully fixed that.

As for the exposure times: Yes, I am aware that there are different exposures and I could have used manual settings. However, in my opinion the panorama stitcher could use the the 1/320 s version as the base one and scale down the others. This would get the full range of tones and user can then use gradient filter or any other measure to make it "viewable".

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However, in my opinion the panorama stitcher could use the the 1/320 s version as the base one and scale down the others.

You might want to change this post to 'Ideas' instead of 'Problems.' I think it's a good suggestion and could be easily implemented.

In general the best practice is to use manual exposure set to prevent highlight clipping in the brightest shot. You might also consider shooting an HDR exposure bracketed file set, which LrC can now process in Photo Merge.

I checked the CR5_1402.CR3 file in RawDigger and it has no significant highlight clipping.

In the below screenshot. I exported the  CR5_1404.CR3 and CR5_1405.CR3 file with -2 EV Exposure to 16bit TIFF and the CR5_1402.CR3 file with 0EV Exposure. I then used LensTagger to change the shutter speed from 1/80 to 1/320 in the 1404 and 1405 TIFF files and then ran them through LrC Panorama. Even without the missing 1403 file the results are pretty good.

(edited)

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Nice trick cheating the Lightroom algorithm with that EXIF change :) That's clever and might be useful on another occasion as well, thanks!

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11 days ago

I got a similar result to Todd's with a different method for getting similar exposures: I used LR's Photo > Develop Settings > Match Total Exposures to match the EV of the two leftmost photos with the rightmost.  Then I did Photo > Edit In > Merge To Panorama In Photoshop.  Then adjustments on the resulting PSD in LR:

The result has the similar blend discontinuity between the middle and rightmost photo, with a distinct change of color of the sky and noticeable blend border in the plowed field at the bottom.  But as with Todd's version, the banding and artifacts in the upper-right corner are gone.

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John,  Match Total Exposures just applies a Basic panel Exposure correction to the files, but LrC Photo Merge to Panorama discards ALL applied settings. They are merged with the exposure matched by increasing the 1402 file Exposure by +2EV, which is what's causing the issue. I get the exact same results using Match Total Exposure, which is apparent after applying the Basic panel settings. (see below)

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Todd. John merged them in Photoshop, not Lightroom, so the “match total exposures” would work

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...and did work :->

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My bad I glossed over the merge being in PS, which does work.

That begs the question of how Match Total Exposure decides what base image it uses for the matching. In this case it works well because it uses the under-exposed  CR5_1402.CR3 image file for the match. In the case here if one could choose the image file to match inside LrC Photomerge Panorama it would also work.

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Match Total Exposures uses the most-selected photo and matches the others to it:

https://helpx.adobe.com/lightroom-classic/help/develop-module-options.html#match-total-exposures 

I've used this technique in some of my own snapshot panoramas where the different auto-exposed shots had wildly different exposures due to extreme lighting (and a couple times to work around the neutral-density-filter bug, which I think is now fixed).

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Thanks for confirming–That makes sense. I'll have to keep that in mind in the future.

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Thanks everybody and especially @John_R_Ellis. This is a good workaround and faster than what I would have used (= Hugin panorama stitcher).

However it lacks the elegance of doing it in Lightroom and especially: Creating a DNG file to work with.

That's why I thought reporting the issue (and perhaps fixing it) would be the cleanest option for the future. That would give us the option of almost HDR panoramas but with much lower number of photos.

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Agreed.                                 

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11 days ago

Another issue makes this example a "hard case": The middle and rightmost photos have almost no overlap, which provides little opportunity for the panorama algorithms to produce a smoother blend.  I'm surprised that they did as well as they did.

(edited)

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John, the OP did not provide the CR5_1403.CR3 that is part of this panorama set. It would be helpful if he uploads that file as well. Perhaps we can then provide other solutions.

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Yeah, I messed up the upload twice, sorry about that. I fixed the second case faster than the first one, but John was still fast enough to download it in the mean time. The zip file should now contain all of four RAW files.

I am a bit surprised it worked that well for you even without one file :) But I work with huge overlaps in case there are some issues (one photo is blurred etc.)

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10 days ago

Using the fourth photo produces a noticeably smoother blend in the Photoshop panorama:

And it retains enough dynamic range that I could add a graduated filter on the right end to bring out some of the details in the highlights and knock down the glare:

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@John_R_Ellis Yep, that's what I do as well typically, though usually through the Hugin route. But it's nice to see the result produced by someone else.

BTW Thanks for your plugins! - A user of Any Filter and Any Vision.

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10 days ago

I've changed this post to an 'Idea' and the title to:

How To Prevent Overblown Highlights in Panorama DNGs

What is being requested is the ability to select a specific image file in the panorama set as the 'base exposure' that will be used to Match Total Exposure of the other files when using LrC Photo Merge Panorama.

In the example here the image file shot into the sun with the lowest exposure value should be used as the base image. This helps to prevent blending artifacts due to highlight clipping when the exposure matched image files are stitched and blended in LrC Photo Merge Panorama.

(edited)

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@todd_shaner_6660895 All right, that would be a good solution. Thank you for the changes.