sRGB mode

[devin]

I'm trying to figure out why the sRGB mode in the VFB seems to slow rendering down so much on interior renderings. My test show that when used with an interior scene my render times go up by 75%, simply turning it off and disabling the "don't affect colors" option in color mapping speeds everything up. All my GI & AA settings are the same in both cases so I don't understand why this feature is there and what it's doing, can someone answer this?

[joconnell]

What are you using as your colour mapping settings? The feature is there for when you want to render in linear but don't want to burn in the gamma change. When any other program like nuke or after effects views your renders afterwards, they'll often put on a gamma correction in their viewer, much like the srgb button in the vray viewer and if you brighten up a dark vray render you'll bring out extra noise in the shadow areas that were brightened up. Don't affect colour in vray tells it that you intend to look at your render in a program with a gamma correction, so do extra sampling in the dark areas that will become brighter afterwards which means extra sampling.

The vfb shouldn't ever make any difference to your render times, the srgb button is just doing a simple brightening of the mid tones of your render, but it's a colour adjustment done on the final pixels and not in any way involved in the actual render calculations.

[instinct]

Because the Samplers are based off the pixel values. For example brighter values get more samples because they contribute more to the visible result (simply speaking). Turning off "Don't affect colors" will burn in the gamma, hence non-linearly change the brightness and can cause all kinds of results for the samplers.

Regards,
Thorsten

[instinct]

Too slow...as usual

[devin]

These are my color mapping settings:
-Linear multiply
-Dark mult: 1
-Bright mult: 1
-Gamma: 2.2
-sub pixel mapping
-clamp output-level 1
-affect background

[devin]

Sorry those are the setting that result in a faster render time, as I said turning on sRGB and "don't affect colors" is what's slowing it down. This also happens on exterior scenes and the final renderings are almost identical.

[joconnell]

Ah yes. The only thing that'll make a difference is turning off don't affect colours - that means that vray is rendering something slightly different. As Thorsten said if you leave don't affect colours turned OFF, it burns the gamma into the image and results in a bright image. If don't affect is ON, it doesn't brighten the image but takes into account that it'll be brightened afterwards and puts extra sampling into dark areas that will become more visible when the brightening is applied afterwards.

[devin]

So if I'm not that concerned about some noise in dark areas leaving it off seems to be a good trade off for the speed increase don't ya think?

[joconnell]

It kind of depends what you want to do with it afterwards - do you do any render element based compositing? Are the renders for print or tv?

[devin]

I don't usually use elements, it's for print and I'll be doing some post work in Photoshop.

[joconnell]

Then screw it! Noise is a huge problem for me working in motion as you'll see it dance right in front of you so I can't afford it.

If you ever get around to using the elements, they don't combine back together properly if the gamma is burnt in so you've got to go the "don't affect colours" route. Again since you're not using this then screw it, if the render looks good with the reduced time then why not

[Zdravko]

as I said turning on sRGB and "don't affect colors" is what's slowing it down

Since V-Ray will do the same amount of sampling in both cases. There shouldn't be any significant render time difference between those.
Would it be possible to send us an example scene to: support@chaosgroup.com?

[instinct]

Since V-Ray will do the same amount of sampling in both cases. There shouldn't be any significant render time difference between those.
Would it be possible to send us an example scene to: support@chaosgroup.com?

Really? I thought the sole purpose of the "Don't affect colors" switch was to apply gamma correction to the sampler only?

Regards,
Thorsten

[joconnell]

I suppose that makes sense if you're only comparing between Gamma 2.2 burnt in and "don't affect colors" which is gamma 2.2 just without the burn in? As opposed to gamma 1.0 being compared with a gamma 2.2 / don't affect colours render?

[Zdravko]

I thought the sole purpose of the "Don't affect colors" switch was to apply gamma correction to the sampler only?

Yes that is right, but in both cases the gamma correction will be applied to the sampler and the calculation will be almost identical.

I suppose that makes sense if you're only comparing between Gamma 2.2 burnt in and "don't affect colors" which is gamma 2.2 just without the burn in? As opposed to gamma 1.0 being compared with a gamma 2.2 / don't affect colours render?

Yes, that is correct.