Proper use of HDR

[Zafar Iqbal]

I suddenly had a thought last night about how to use HDR images properly, or rather - how to most realistically extract the HDR data.

I usually just import an HDR image and then slap it onto a dome, adjust the intensity to match the kind of ligting im interested in and thats basically it - but most HDR images looks overexposed - so the question is: would the correct usage be to tweak the HDR setting in such a way that it visually appears correct (matches final render look), and only then take it from there?

I can archive satisfying renders, just as I can with the old school method of working with 3D (non linear workflow), but I'm trying to dig deeper into things to archive that more knowledge which ultimately should result in that much better/realistic renders and less trial and error stuff.

[cryptosporidium]

well i think you definitely shouldnt use Intensity node with hdri. You can tweak exposure, but i think you shouldnt use any other methods to tweak hdr image in XSI. Talking about exposure, it doesnt really matter what intensity you use. If you render float or at least half-float output, no intensity data are cropped and you can tweak brightness later on in your 2D software. By adjusting gain value you do basically the same thing as when you tweaking intensity (exposure) of lights or hdr image in XSI.

[Zafar Iqbal]

It was just a generic question. I've been more focused on how colors and shades appear after I began digging into linear workflow not too long ago, and while playing with HDR (in a different 3D app, actually), I could see that something was off.

I thought I was working in "linear workflow mode", but after a bit I realized that I wasn't. That's what I was noticing, and because of my false assumption, I thought that maybe HDR images needs some further tweaking.

Only needed to correct the output gamma - everything looks a lot better and more predictable now.

[cryptosporidium]

well, you know, unless you are using something like maxwell with "physically correct" lights and "physically correct" materials, everytime you will need to tweak your scene bcs most of things in 3d are fake and doesnt work like in real world. But in my experience, hrdi should be the last thing you should tweak in other terms than exposure and gamma. Moreover, if you want "physically correct" renders you should consider also things like Tone mapping (look up in mR docs), bcs physically correct render would be like when you take a photo against a window when its a bright day outside - overexposed windows and extremely underexposed everything else what isnt directly lit by the sunlight. And its probably not what you are after.

[Zafar Iqbal]

Problem, to be exact, was that I used a bitmap texture that I had gamma corrected, while I didn't tell the app that I was aiming for linear gamma workflow. And because of this, the colors on especially the texture looked off - I was just too quick about wondering if it had anything to do with HDR, because it didn't.

So no problem really - just an ordinary error 40 :o