What does this exactly mean.

[WWX]

Under the Colour Mapping Tap, there is an option to tick "Don't affect colours (adaptation only). What exactly does this mean.

I have noticed that my image is much lighter (in the shadow areas) when this is ticked on, compared when not. But which option is the correct one as in reflecting more closely what the exposure would look like in real life with the given settings.

I follow a LWF, well at least I hope so and are using the VRay Sky and Physical Camera.

Thanks

[joconnell]

Sometimes people prefer applying a gamma curve in post so it's related to that. When vray renders, it normally tries to get an even level of noise across the image so that the highlights, midtone and shadow are all of a similar graininess. If you use lwf in post where you apply a 2.2 curve or similar, you end up brightening your shadow area a lot. Vray unfortunately isn't aware of this though, so when you apply your gamma curve it makes the shadows a lot brighter and in effect pushes the noise up a lot more in those areas.

If you render using lwf where the gamma is applied in vray it can take into account that you're brightening the image in the shadows and sample accordingly so you get your bright shadow areas but again an even noise across the image. Adaptation is to be used when you will be applying a gamma curve to the image in post, but don't want massive grain in the shadow areas. What it does is tell vray that you'll be applying a gamma curve after the render takes place so take that into account when sampling - the main effect of it is that when you apply your gamma curve afterwards, it's not as noisy in the shadows.

[percydaman]

excellent answer joconnell. Though I think you answered the question like 3 times in 3 different ways.

[joconnell]

I seem to that a bit - used to be a lecturer and i found that you need to look at things different ways since people learn in different ways - must pare back some of this stuff on a do a proper doc on it to save peoples time from my ramblings

[WWX]

I am still not sure about what to do (don't worry the short coming is not in your answer but my lack of knowledge/understanding of LWF)

Let me phrase my question like this:
I have a good understand of photography as for what shutter speed/f-stop combinations will be required for a given scene and how to manipulate these values to achieve the effect i want.

I would like to use this knowledge in VRay, since I will be working with the Physical Camera.

My Max gamma is set to 2.2, I use Linear multiply for Colour Mapping and the gamma is also set to 2.2 under this tab.
I render out to VRay's VFB where "Use colour correction curve" is switch on and the curve is set with the left hand point's tanget at 0:0.64 and the right hand point's tanget reset.

With these as my starting point, should i switch "Don't affect colours" on or off before I start playing around with shutter and f-stop values? (I won't be playing with the gamma curve on post)

Thanks

[dlparisi]

Keep in mind that the "Don't affect colors" option affects ALL of the settings in the color mapping rollout (type, multipliers, clamping, etc) and not just the gamma. It effectively forces a linear, full float image, albeit with the sampling done using the color mapping settings. This could be why your shadows look different when it is checked vs. unchecked.

The impact of the checkbox isn't really evident by the layout as the "Don't affect colors" checkbox is just another in the list of settings. IMO, it should be placed in a new group box with a better description of what it does but this is a minor quibble.

[dlparisi]

My Max gamma is set to 2.2, I use Linear multiply for Colour Mapping and the gamma is also set to 2.2 under this tab.
I render out to VRay's VFB where "Use colour correction curve" is switch on and the curve is set with the left hand point's tanget at 0:0.64 and the right hand point's tanget reset.

With these as my starting point, should i switch "Don't affect colours" on or off before I start playing around with shutter and f-stop values? (I won't be playing with the gamma curve on post)

First off you can forget about the "Use color curves and setting to .64...". Leave those off and click the "display colors in sRGB space" at the far right of the icons. It's more accurate and is easier (it wasn't available when throb did his original tutorial).

For the setup you describe you should check the "Don't affect colors" option, otherwise you're double correcting your image since you're adjusting the display by the "sRGB" button. Alternative you could leave it unchecked and also unclick the "sRGB" button in the vray VFB and get nearly identical results (see my post above)

[WWX]

Cool Thanks

[joconnell]

If you're using the gamma control in the color mapping dialog then it means you're burning the curve into the image so vray will sample properly to get even noise in the shadows - the only time you'd have to use the "don't affect colours" option would be if you were rendering to a non-lwf image but you were applying a lwf curve in post.

However if you are enabling the max gamma and also using the vray gamma it sounds like you're applying gamma to your images twice - vray will use the max gamma settings in place of its own colour mapping settings so be careful you're not double correcting your images.

Here's a case where you would use the "don't affect colours" option

1. Max gamma is set to 1.0
2. Vray colour mapping is set to 2.2, "don't affect colours" is turned on.
3. Image is being rendered to the vray frame buffer
4. Either the srgb button or use colour correction curve is turned on in the frame buffer - this is for preview purposes only - it won't actually save with the image itself unless you save the file from the vray frame buffer
5. A 2.2 curve is applied to the image in photoshop, nuke, after effects or another compositor.

[WWX]

Damn just as I think I am starting to understand

dlparisi, if i use the sRGB option, safe the image out from VRay VFB and open it in PS the image is much darker, just like as if the sRGB button was not on at all.
If I use the curve option the image opens in PS as it displayed in VRay's VFB.

joconell, if I use the sRGB option switch on and have Max gamma set to 1 and then copy the rendered image from VRay's VFB to Max VFB the image is also dark, as it would be if i switch sRGB off in VRay VFB.
With Max gamma set to 2.2 the two images look the same.

[dlparisi]

The sRGB option only changes the colors as they are displayed on screen but doesn't change the values, unlike the curves option. AFAIK, you can solve this by either saving the image as an .exr (my preference), change the bitmap output gamma to 2.2 (I'm not sure what else this would screw up), set the Gamma in the save image dialog box to 2.2 (instead of system default), or just apply a 2.2 gamma exposure correction in photoshop. Depending on your workflow though one option may be better than another and I'm not sure that the last two are all that accurate.

For your second question, the max VFB is aware of the Max gamma setting and adjusts the image accordingly. The Vray VFB does not use the max gamma setting so checking the "display sRGB" button should make them match. I don't think setting the Max gamma to 1 is a good idea as you're definitely not working in LWF at that point.

Since your not going to be adjusting the gamma curve in post, perhaps the easiest way is to just leave the "Don't affect colors" button OFF and just use the Vray VFB as the default. You can save your images as JPG's or TIFF's and everything should look OK in Photoshop.

John?

[joconnell]

Yup I'd agree - simplest method is to set either the max or vray colour mapping to 2.2, set the max bitmap input gamma to 2.2 so your texture maps are aware you're working in lwf and then render to whatever format you want.

[rivoli]

Since your not going to be adjusting the gamma curve in post, perhaps the easiest way is to just leave the "Don't affect colors" button OFF

I guess "don't affect colours" comes really handy when you want to work with full float formats, and have vray doing the best sampling at the same time.
if you wanted to have vray sampling a linear image, you had to gamma correct via colour mapping. so I guess you couldn't save to a linear format such as exr or your render would have been double corrected. now you can tell vray to do the sampling for a gamma corrected image without affecting the actual colours, so I guess you can either save in a ldr format and gamma correct later, or output directly to a hdr format.

[dlparisi]

Since your not going to be adjusting the gamma curve in post, perhaps the easiest way is to just leave the "Don't affect colors" button OFF

I guess "don't affect colours" comes really handy when you want to work with full float formats, and have vray doing the best sampling at the same time.
if you wanted to have vray sampling a linear image, you had to gamma correct via colour mapping. so I guess you couldn't save to a linear format such as exr or your render would have been double corrected. now you can tell vray to do the sampling for a gamma corrected image without affecting the actual colours, so I guess you can either save in a ldr format and gamma correct later, or output directly to a hdr format.

Exactly. I've also had trouble with extreme black gradients on a 2.2 gamma image resulting in some very odd colors (reds, yellows, etc) but I believe this has been more or less corrected for 1.5. In a quick comparison on 1.5 though, I still notice a slight difference in the black levels on a linear vs. 2.2 gamma image (the 2.2. gamma's black levels are slightly higher); the odd colors are gone though. I just mention it as another reason to possiby not use the 2.2 gamma on some images.