Force Colour Clamping

[sebbiej]

Hi all,

I?m just looking to clear up a bit of confusion that I?ve got with the Force Color Clamping option in the V-Ray Frame Buffer: I?ve always kept this option on to stop with the rainbow effect colours that you get with it switched off. But, I?ve been doing a bit of reading up on the Chaos Group forums and it seems like I may have been working wrong all this time!

Am I correct in thinking that I should keep the Force Color Clamping option off, and use the ISO setting in the Physical Camera attributes to correctly expose my image instead (as in bring down the exposure until those colours beyond pure white are at 1)?

For example; should I raise up the ISO until I just about reach the point in which the clamped rainbow colours are visible, and bring down the intensity of my light sources if they?re going way beyond the clamped limits? Then, raise up the exposure of my renders in After Effects in post, as my current scene is looking a tad dark now.

I?m currently trying to match some photographs of an interior scene that I?ve re-created in 3D, but if I match the same kind of intensity of the real-life lights with the V-Ray lights, the image in the frame buffer shows quite a lot of whites that are way beyond pure white (if that makes sense).

I?m working with my Color Mapping set to Reinhard,

Multiplier = 1.0,

Burn = 1.0,

Gamma = 2.2,

Mode = Color Mapping only, no gamma

Clamp Output switched off.

[vlado]

It looks like you simply need to adjust the exposure on your camera after you add the V-Ray physical camera attributes to it.

Best regards,
Vlado

[RobH22]

I've been reading for an hour and I can't find a thread that suggests what the default setting of 'Force color clamping' is. Should it be 'On' of 'Off' by default for a standard workflow?

[dgruwier]

The reason you're getting over-exposed areas when you match your lights is that the frame buffer (unless you tell it otherwise) displays the scene as sRGB, and the camera is using something else that has lower contrast / higher dynamic range than sRGB. It's not unlikely that you actually matched the lighting in the scene pretty well, and that if you converted the raw photos from whatever color space the camera is using, into linear, then into sRGB, you might see the same over-exposed areas.

It's a complicated and technical subject that I don't really know much about myself (and which is probably why you're finding conflicting answers), but suffice to say that can't match the photo exactly by only adjusting the lighting in the scene. I'd suggest trying to get closer by adjusting the Exposure, Contrast and especially the Highlight Burn value in the Color Correction section of the frame buffer.

As for the color clamp, I suppose that's just a tool to diagnose your image. If you don't want to look at weird rainbows, leave it on. If you absolutely need to make sure that there are no white pixels in your image, turn it off for reference. Otherwise just use your eyes.


One last note, this is all assuming you're not rendering directly to .exr files and using those in AE and bypassing the frame buffer, in which case you need to make those corrections I mentioned before directly in AE using linear workflow.