P: Export Tiff/PSD with Transparency to PNG with Upscale produces unexpected render

[FuturamaFry]

When enlarging and exporting a file with a transparent background as a PNG file from Lightroom this happens

PlatesOutside177Edit-2bcf25aa-3074-4602-85c6-42786b7c066d-1378061682.png

[Victoria Bampton LR Queen]

Could you take us through your exact steps please, particularly how you are enlarging and your export settings.

[FuturamaFry]

Yes. I start with this image from within Lightroom. It's an NEF file.

From within Lightroom I "edit in photoshop" to remove the background. The example I initially posted was a quick and dirty version I did with customer service. When I've finished removing the background from around the plate as well as the bolt holes I save it, then go back to Lightroom. Once in Lightroom I export as a PNG, sRGB color space, 8bits/component. I enlarge the Long Side to 12,000 pixels with a Resolution of 300.

This same thing happens with images that already have the backgrounds removed as well. The image below had a transparent background, was imported into Lightroom with a transparent background and upon export, enlarging the image by 1000 pixels, it rendered this way:

[FuturamaFry]

I should also say, Lightroom Classic 10.0 being used on a Mac running Big Sur though it was also happening before I upgraded the OS on the Mac. It was not happening before I upgraded Lightroom Classic.

[Bob Somrak]

Works fine for me on macOS 10.15.7

[FuturamaFry]

What version of Lightroom Classic did you use and what were your export settings?

[Bob Somrak]

Strange, I did a couple other photos and they both exhibit the problem so I got one good result out of 3!!

BTW, PNG files seem like they take a LOT longer to export than they should.   They take longer in Photoshop but in Lightroom they take an extraordinary amount of time to export.  

[FuturamaFry]

I found that as well, I think it takes longer because it's adding all that extraneous data to the file. I'm relieved that someone else was able to duplicate the problem - proof that I am, at least, not crazy.

[Bob Somrak]

This is definitely a bug.  The only thing I use PNG files for in LR are Identity Plates and Watermarks so haven't noticed it. 

[Rikk Flohr: Photography]

So to recap:

Tiff/PSD with Transparent Backgrounds

Exported at larger than original size exhibit this behavior. 

Is that correct?

[FuturamaFry]

@Rikk

I would add PNG to that as well as I've imported PNG files and tried to export them larger and it exhibited the same error. So - 

Exporting as a PNG larger than the original size exhibits the error. 

I don't know if it's important but I think there is a threshold of enlargement as well. When I was troubleshooting I could successfully export if the enlargement was small - when I enlarged the large side form 6,000 p to 7,000 p it did fine, but going up to 8,000 p the error was there. That has been my experience anyway. 

There should be a vid of the CSR attempting to correct the issue via my computer - Case number: ADB-16432718-F5M0 - if that's helpful and you run in those circles. I can't imagine it's all that exciting...

[Rikk Flohr: Photography]

Thanks for the info. I will try to reproduce.