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HDR blur artifact

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I load a .hdr file such as the St.Peters cube cross in HDRshop.

I ask HDRshop to gaussian blur it with a large kernel, say 256 if each side of the cube is 256x256.

I get a smooth and slowly varying blurred result.

But if I reduce the exposure few times thus darken the image, if you look closely, why are there quantization ringing artifacts everywhere?

Notice I captured the pictures as png, not jpg.

Thanks

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I did not check the pictures in any editor because png is just 8-bit anyway IIRC, and you would should check the colors in the hdr image.
However I can see the quantization effect which is probably due to my monitor running on 6 bits per color (instead of 8) something I think is quite common these days.

Can you verify, that the quantization effect is also in the hdr image by looking at the numbers, not the colors?

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I moved the mouse along one band and look at the pixel values displayed by HDRShop. Do the same for the adjacent band. The average pixel values do seem to be different.

To see this download HDRShop and some environment cross hdrs at the bottom of this page
http://ict.debevec.org/~debevec/Probes/

I do wonder if the non-free version of HDRShop has the same effect if anyone has it.

Thanks

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You might want to try CubeMapGen for this. It definitely does its calculations in high precision, and will also do proper filtering with regards to cubemap texel extents.

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