Uneven brightness between adjacent panorama frames

Report · Oct 22, 2021

I have been shooting panorama for about 20 years, and developing the raw files in ACR. One of the key principles of panoramas is that all of the adjacent frames in the series be captured with the same exposure, and then developed identically, so that the brightness of of the shared, overlapping content is the same between adjacent frames. Otherwise, there can be obvious and brupt transtions of brightness across thepanorama. this is particuarly evident in skies.

I have been ACR along with Photoshop for this since CS2, without major problems. As part of my conversion to a Canon R5 I upgraded from CS6 to Photoshop CC and its associated Camera Raw. Since then I have been having signficant problems with images that were shot with the same exposure in a panorama series, and developed with identical settings in ACR, having greatly different brighness in the same subject matter shared by adjactn images. This results in the uneven tonal transitions across the panorama described above. I have had several projects where this is so severed that I simply cannot complete what would otherwise be a usable panorama.

What is happening is that when the Shadows and Highlights sliders (in particular) are used, ACR looks at the brightness of the entire frame and "decides" how much to adjust the shadows or highlights of the individual frame. It does this differently for different frames, even for the same content in adjacent frames. For instance, I have found that if one frame contains more bright areas (for instance, more sky) than the adjacent frame, ACR will increase the shadow brightness more than for the adjacent frame that has less overall bright area. As a result, the overlapping content that is included in both frames is rendered to a different brightness, even though their expoure was the same and the ACR adjustment was the same.

I have found that this does not happen when only the Exposure slider is used. But of course for most images, adjustment of other control,s Highlights and Shadows in particular, is needed. I have not found a solution or workaround for this, and a result I am unable to use wht would otherwise be perfectly good panormas. I cannot simply manually lighten or darken each individual image to try to match the ones around it. The highlights and shadows are adjusted differentially between the different images and are no n the same proportion to each other, so a change in overall brightness wiould still not match the different elements of the image.

I have done some research and gotten input on other forums, which confirmed that this is a real phenomenon, stemming from improvements Adobe began making starting after Process Version 2. For single-frame image it is defintily a "feature", as the shadows and highlights are intelligently adjusted to optimize the entire image. But for panoramas, where identical adjustment of adjacent frames is critical, it is a real problem.

So short of reverting back to process Version 2, can anyone suggest a solution or workaround to avoid this problem?

Attached is an example of a pair of images shot with the same exposure, within seconds of each other, and with the same adjustment settings applied in ACR. Note that the rocks that are included in both images, as well as the sky adjacent to them, have a singificantly different brightness. Becasue the image on the left has more overall bright areas included in the full image, the Shadows slider lightened the shadows to a greater extent than did the same slider adjustment on the image at right. Stitching these two frames result in an obvious abrupt tonal transition in the sky and across the rocks.

Thanks in advance for your thoughts and advice,

Dave

Report · Oct 22, 2021

Yes, although Shadows, Highlights, and other Basic panel options are great features for a single image, it’s true that they can have unwanted side effects when applied to images that will be combined. Those options cause similar problems for time lapse photography.

One way to work around it is to go back to the old way of adjusting contrast: The Tone Curve. It does not take nearby pixel values into account, and does not do any automatic masking or detail recovery. All it does is shift all pixels of a certain value. But that keeps the adjustments more consistent across multiple images.

For example, if you want to brighten the shadows, avoid using Shadows in the Basic panel, and instead increase the brightness of shadows using the Tone Curve. It’s true that Tone Curve adjustments are less powerful and have other tradeoffs, but there are also many cases where a Tone Curve adjustment can work nearly as well as a Basic panel adjustment.

Report · Oct 23, 2021

Thank you Conrad. That gives me a route to explore. Currently I do the major adjustments with Shadow/Highlights, and then fine tuning with the parmetric curve. I could try reversing that strategy and do the most signficant balancing of shadows and higlights with the curve, and then make relativly minor final adjustmens with the sliders. That's at least worth a try.

Any other suggestions would still be welcome.

Dave

Report · Oct 25, 2021

There are a couple of workarounds. One is to wait until the pano is joined into one image and then make global adjustments. Another would be masking to protect problem image areas (Adobe has announced new, advanced masking in the forthcoming ACR release.) Finally, you can edit the same image multiple times with different settings, stack the duplicate frames, and mask out things like the sky that you don't want changed. Obviously 1 and 3 require work in Photoshop once the pano frames are assembled.

Report · Oct 25, 2021

With respect to the first idea, the panorama cannot be assembled until it is a raster image. ACR (and Lightroom) work with a raster version of the raw file to show the effects of editing that would eventually be applied to the raw image. Lightroom can form that raster image into a preview of a panorama. But I belive (correct me if I am wrong) that this panorama is no longer a raw image; that is, any edits made to it would not be to the raw data but rather to the rasterized version of the original raw files. I believe this would be the same as converting and saving the raw files to tiffs wthout any adjustment, then importing the tiffs into ACR or Lightroom. While obviously adjustments can be made to jpeg and tiff files by ACR and Lightroom, that is not the same as making adjustments to the raw data. I would vastly prefer to take advantage of my raw files to make the optimal adjustments to them before committing then to tiff or jpeg images.

Please clarify if my assumption regarding the panorama produced by Lightroom is incorrect.

Of course, ACR does not have the ability to produce a panorama that Lightroom does, and I prefer ACR over Lightroom for developing raw files. Currently I make optimal adjstments to the raw data in ACR, then save them as 16-bit tiffs. I use PTGui Pro to assmble the individual images into a panorama, and take advantage of the advanced features in that specialized software. I would not be eager to be confined to producing panoramas with the limited panorama features included in Lightroom. So I would still greatly prefer to develop my raw files (with the same adjustments and the same effect on all the overlapped images) and then be able to work with those files in PTGui.

Thanks for you other suggestions. I will look into the masking and multiple development, but I suspect that it will be difficult or impossible to produce seamlessly matching tones across all parts of the overlapping images when ACR is making applying differential adjustments to the same content in all the images.

Dave

Report · Oct 25, 2021

@Dave Johnston wrote:

Lightroom can form that raster image into a preview of a panorama. But I belive (correct me if I am wrong) that this panorama is no longer a raw image; that is, any edits made to it would not be to the raw data but rather to the rasterized version of the original raw files.

Sort of in the middle. The panoramas created by Lightroom Classic and Adobe Camera Raw are DNG files, which are much closer to raw than to an JPEG or TIFF image, so if you continue to edit a DNG panorama, the controls you get are raw controls (for example, white balance is absolute, not relative as it would be if editing a JPEG or TIFF).

You could use this to implement the type of editing discussed earlier, where you talked about using the Tone Curve first for major moves, and Basic Tone panel options for minor moves to minimize their artifacts. After applying Tone Curve adjustments to each raw file, you could merge them into a DNG, and then apply Basic Tone options to that. Because they would be applied to a merged image, you wouldn’t have frame-to-frame artifacts, and because it’s DNG, it should retain more quality than a TIFF. Unfortunately, that still won’t work with a PTGui workflow because they’re getting merged before they get to PTGui.

@Dave Johnston wrote:

Of course, ACR does not have the ability to produce a panorama that Lightroom does, and I prefer ACR over Lightroom for developing raw files.

Actually, Lightroom Classic and Adobe Camera Raw have the same set of merge features: Merge to HDR, Merge to Panorama, and Merge to HDR Panorama. Below is how you get to them in Camera Raw 13. Note that Lightroom Classic and Camera Raw use a panorama algorithm that is different than the one Photoshop uses, with different options.

Although Adobe has announced advanced masking in an upcoming release, that is probably not going to help, because you would have to preview how the images merge before you can know how to mask off the visible seams. That’s possible by using the panorama preview before merging, but it would involve so many trips in and out of that dialog box and so much manual masking that it would not be enjoyable.

I still think the best though still non-ideal approach is to go as far as you can stand with the Tone Curve, then refine that by applying minimal Basic Tone panel options, then export for merging in PTGui. It may take a few test runs to see how high Basic Tone options can go before creating problems at the seams.

Report · Oct 25, 2021

Thanks Conrad and Lumigraphics. I am embarrassed to say I hadn't noticed that ACR could now render panoramas. I recently migrated from CS6 (which I don't belive had that) and had not even looked for that capability in ACR. That may be useful as an alternative where for whatever reason I don't need the additional strengths of PTGui. And if nothing else I could use and ACR-produced pano as a target for adjustments of the individual files using the tone curve methods you suggested. Thanks you both for your ideas.

Dave