Panorama has skewed colors

[lphilpot]

It doesn't happen in every instance, but look at this:

The left image is one of the source JPGs and the right image is the same region from the Photo 2 panorama. There's a significant cyan / green shift in the color. It's more apparent in this larger view:

This is what the sky should look like:

I made no edits, just cropped the pano to opaque, saved as afphoto and then exported to JPG. I tried both using the document profile and explicitly specifying sRGB when exporting but the results were identical. At any rate, the skewed colors were visible from the outset in Photo as soon as it was stitched.

However, I created another pano from different images and it came out OK. I even tried starting from raw, converting to both JPG and TIFF (in another raw editor, not in Photo) and then stitching the TIFFs and JPGs. Both were OK.

So what triggered this issue?

[lphilpot]

Apparently no one has run into this before, but a couple more data points...

The images look good color-wise on the new pano dialog, best I can tell at such small size:

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And it looks normal enough while rendering:

But when it completes the colors go bonkers:

Given that I've done other panos In Photo 2 without this issue it's somehow related (at least) to these images, apparently. But why does Photo screw up the colors? Is it an issue with the images or with Photo 2? These same images looked fine in Photo 1 (alas, no longer installed).

I've attached the images if someone is curious enough to try them.

panorama_with_skewed_color_source_JPGs.zip

[Old Bruce]

May be due to the odd Colour Profile on the JPEGs

But I would think that this set of pictures is perhaps too challenging, we have massive areas of blown-out highlights on the left are competing with the average blue sky on the right.

[lphilpot]

Could be, but that's just the standard sRGB profile bundled with RawTherapee. Plus the very same images worked fine in Photo 1.

Hmmm...

Just for giggles I might reprocess their raws again and try with new exports. 

[loukash]

6 hours ago, lphilpot said:

Apparently no one has run into this before

I have.

6 hours ago, Old Bruce said:

May be due to the odd Colour Profile on the JPEGs

No.

The issue is likely the algorithm which attempts to find a "common ground" in images that may slightly differ in brightness and contrast.
I don't do any photography panoramas, but I'm using the Panorama feature literally hundreds of times for stitching oversized scans, mostly LP covers scanned on a standard A4 scanner in four passes (remember: an LP cover is over 12×12"). Color shift like in the example above happens quite often, mostly because the algorithm gets confused by shades and shadows caused by the scanner area rim where the LP cover is not lying totally flat on the glass. (At least though, I have "old fashioned" CCD scanners which have a quite wide range of focus depth, unlike the cheap CIS scanners these days, so even though not fully flat, those areas are at least still sharp.)

It takes some time, but in most instances it can be fixed by manually defining the preferred areas with the Add to Source Image Mask tool. But you really need to go by trial and error to get the feeling for it. As in: in the meantime, I already know what to look for when using the tool, and have an approximate idea what the expected result will be. But there's no "general fix".

[lphilpot]

I was curious so I reprocessed the raw images and tried again.

This time it wasn't raw-converted in Photo but it wasn't before, either. I've tried Photo's raw persona and it's OK but kinda meh... Anyway, I created JPGs this time for some consistency with before (not TIFFs per usual). I'm sure my processing wasn't identical to last time, since it was a slightly different raw editor (ART vs. RawTherapee) and I didn't attempt to totally replicate the earlier images. I just tried to get a reasonably good image, given the time of day, etc. I dropped exposure by 1/3 stop and added a slight bit of highlight precompression to remove a few blown highlights (of which there were only a few), bumped the black point a hair, did some basic L*a*b* color adjustments, a tiny bit of dehaze, etc. I then used that same profile for all images.

Once stitched in Photo, I denoised it slightly as there was a hint of highlight granulation in the sky highlights, added a little high pass sharpening, cropped and exported at 4k pixels wide. The original is over 18k wide.

This time it came out OK, so who knows...