Peter Guthrie Hdri exposure

[francomanko]

Hi, i'm wondering if i've been using Peter Guthries hdri all wrong.

So these hdri maps have large dynamic ranges, presumably to get sharp shadows, so when i use them as is, the render is completely blown out. Usually i use a physical cam to bring it into the correct range. Now if turn on show in viewport, its just white....to get this to work i have to reduce the textures color gain value to , lets say 0.1. But obviously this affect the render too.

In max I think you can set the render gamma separately from the viewport gamma...so my questions are

1. Is my workflow wrong
2. Do i keep the hdri map gamma, as is..for the render and then is there a way to change this value for viewport? Or do i need to adjust the gamma until it looks correct in viewport and render with that?
3. Am i just old and confused?

thanks for help, any workflow tips would be much appreciated.

[francomanko]

ok so

To get the viewport hdri looking correct, i have to set the light intensity to 0.025. So I suppose the question really is...

1. Do i set the domelight intensity to a value where it looks correct in the viewport, and render with these settings?
2. Or do i leave intensity at 1 and adjust the exposure with the physical camera settings, and if so is there a way to independantly control the viewport intensity?
3. It doesnt matter either way?

I'm presuming its number 3, but i wanted to check.

[dgruwier]

It's not unusual for an HDR to blow out a scene, especially if it's an outdoors HDR with a sun in there or something like that. You need to make sure the HDR is linear in the render, that's the important part, other than that you shouldn't have to fiddle with the gamma.

How you deal with the brightness of the HDR is up to you, depends on the situation, so option 3 I suppose.

[seandunderdale]

I have asked before the difference between changing Dome light intensity and camera exposure, the answer was "none". Changing F-number and shutter speed will affect DOF and MB, but changing ISO, I was told, is the same as changing Domelight intensity, so it doesn't matter which you do.

What Ive found with high quality HDRIs (and by that I mean assets from HDRI-Haven and not from places like Maground) is that you often need to tone-map the image to control the overexposed areas. If you take a photo of a metallic car paint at an angle where the sun is hitting it to reflect into the camera, this is the result that you get in Vray linearly. Ive found that using "Exponential" with 0.4 dark and 4.0 bright gives a result the eye would expect to see. These can vary depending on the shot, but Ive gotten some accurate results in the framebuffer when matching to a photo stand in car.

As mentioned above, do not change the gamma of your HDRI. Remember, this is a capture of the environment, and aside from white balance, and some software processing (Lightroom / PT gui etc) it should be accurate to the scene you are dropping CG into. I find that as long as the sun exposure / intensity is correct, relative to your sky, then you should get very realistic results.

[francomanko]

thanks for replies, much appreciated.