HDRI - What's the best way to re-size?
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When using HDRI for lighting a scene every tutorial out there points to having two versions of the same image, a high res and a low res version of the same. I surmise is to most effectively use processing power. But, if you have say a high res hdri only, what is the proper way to create a low res version of the same without screwing things up?
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With sIBL-Edit you can automatically generate an environment (low resoultion), reflection and background maps starting with a HDRI.
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Cool! Thanks. I'll give that a try.
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As long as you open and save in 32 bit you'll be fine. This is another technique and some info:
If you have photoshop, save the high res version as a jpeg. You must change the mode to 8 bit. Photoshop will prompt you to tonemap the image. Just choose the exposure/gamma setting and it won't tonemap the hdr any differently; the jpeg will look the same as the hdr. So now you have high res jpeg of the hdr.
Open the original hdr (32 bit) and just change the image size and save. Normally 4000 pixels wide is enough. This will be your lower res hdr for lighting/reflections.
I have tested 4000,5000,6000,10000,14000 etc....and I see no visible difference to reflections to be honest. Some render engines won't even load large hdr files.
The only thing that is better with a high res hdr is the background clarity. But what's the point? You just swap your background for the high res jpeg and it renders MUCH quicker. Plus this allows you to increase brightness of your hdri but keep the background the same exposure; more flexibility.
As a general rule, and as with my hdri packs, 4000x2000 for the hdr and 8000x2000 for the jpeg. A 4,000 pixel wide hdr can be 20MB while the full size 14,000 pixel wide version is 260MB!
Playing with jpeg compression can also shave lots off file size for your background.
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Thanks Oli! Superb!
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