Got an issue that confused me and suprised me that I couldn't find an answer by googling...
When I try to export one of my panorama pictures using "Export as", Photoshop (V21.2) automatically scales down my pictures and gives following message: "The image's initial dimensions exceed the maximum allowed pixels and having be downscaled".
What caused this problem? Did I do anything wrong?
Ok, that explains part of it. It was flattened but 32b.
But it doesn't explain why the export-as started working after rebooting PC.
Under file, do "Save a copy". It'll allow you to save as a jpeg at the big size.
This should not be a problem. The image is too big for the web. For the web, make it smaller. For non-web use, use SAVE AS or SAVE A COPY in the usual way.
Ok, how can I check what are limitations?
The dimension limitations for Save for Web are 8192 × 8192 pixels. That is why a long dimension above 8192 is reduced to 8192. The limit exists because Save for Web is very old code, and that is why Adobe has named it Save for Web (Legacy). They want to remove this old command eventually.
There is a much newer command for web graphics export, intended to eventually replace Save for Web (Legacy). The new command is File > Export > Export As. The Export As command has no problem allowing and exporting a 9000 × 1920 px image in JPEG format.
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I suggest you archive the original (tiff or PSD ideally), make a copy, resize the file manually, sharpen, convert to sRGB then use "save as" and set it to Jpeg
some notes on Jpeg
Jpeg is the worst possible format if you want to keep high quality - you should always archive a copy of your original, with adjustment layers intact - if that’s how you work.
Jpeg compression (at any setting*) really is "lossy”, irreversible and cumulative, so should ONLY be used only for final delivery AFTER resizing & cropping to the FINAL size and crop.
Why? Any edits to size or crop, or even just re-saving a Jpeg file means further compression, potentially that’s very damaging.
The jpeg damage is not always immediately apparent, which is perhaps why it's still widely used - however, the compression will soon cause issues if you do further work and save again. That’s when you’ll see a jpeg with some real issues.
*don’t imagine that selecting maximum quality for your Jpeg is preserving the original data, it’s still compressing a lot which discards information.
I hope this helps
neil barstow, colourmanagement net - adobe forum volunteer - co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management