the manual says: limit 8192 on various places. The higher values are not referenced at all.

I just loaded a 32.000 x 1024 JPG, and it's succesfully converted to 32bit-EXR in TextureCache for rendering, and it rendered fine.

the preview limit is indeed 16.384. But that's for preview, not for rendering. An OpenGL thing perhaps, or just practical (why does one need a preview resolution that dramatically exceeds monitor capacities?) 

I think the manual is outdated. 

test2: I loaded a 129.000 x 300 PNG. It generates a message on out-of-memory after selection, I click [ok], I select the image again, and all is fine. EXR created in TextureCache of the proper size, and rendering is fine. Same for 65.000 wide images. Same for 33.000 wide images. But 31.000 wide image does not give the message.

I guess 32768 is the message-limit, but you can ignore them: limits are off. Have fun.

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though