Exponential color mapping - background image elements

[Lupaz]

Hi all,

I couldn't find the answer with a search on the forums.

If you use exponential color mapping or other than linear, how do you keep your images that create parallax from being affected?

In other words, the images (bitmaps) I use on the background placed on planes (I don't use 3ds max's background) change their original color. I can't use linear color mapping because it's useful for my foreground elements.

Is there a way to exclude certain objects from exponential color mapping? (this question was asked before in 2007! no answers though).

How do you deal with this?

Thanks much.

[Slazzo]

I would apply a reverse exponential curve on those backplates, but best is to compose them in post.

[Lupaz]

I was hoping not to have to do that in post. It's coming pretty good straight from 3d except for the plates.

HSV exponential isn't bad actually, but it affects the entire render. It would be great to have a texture map/material that could be used to exclude objects from being affected by any curve during rendering. (I am aware that working in full linear workflow is better, I just don't want to)

[samuel_bubat]

I think there is no way to exclude textures from the color mapping other than the background image from the global environment slot
(untick affect background in the Vray environment dialogue).
But you can adjust the curve of other textures by hand. You can do this in the "output" rollout within the bitmap. Also give Reinhard tonemapping a try. Usually you just need to
turn down or up the curve a little depending on how your settings are in the exponential or similar color mapping. There is no real way to say how your color curve looks like
just by settings because it changes when you adjust the parameter of a tone mapping. But there´s a way to "extract" the color curve of a rendering. But it´s a bit
more to explain. Tell me if you´re interested.

[Lupaz]

Thanks Samuel.
I believe what you are suggesting with the output options is what Slazzo was saying, no?

It seems that that's the way to go. It's just that being these"self-illuminated plates" so popular, I'm kind of surprised that there isn't a way to bypass the color mapping curve for specific objects as opposed to letting it apply the curve to the texture and reversing that with another step.

May be I'm surprised bc I'm ignorant in programming.
But perhaps chaosgroup has a workaround with a script or something. Like a macro that automates what you guys are suggesting.

[Slazzo]

I guess an experienced scripter could write a map plugin that will invert the color mapping settings for the texture, maybe not 100% accurate, but I think it's easier for chaos to add a checkbox in the vrayHdri map.

[Lupaz]

ChaosGroup? Is there something like what Slazzo says hidden somewhere? other existing alternatives?
thanks.

[tashko.zashev]

Hi,

I think you could derive the unmapped object/material, if you use V-ray Material select render element with "Color mapping" option "Off".
About the color mapping check-box in the HDRI map, maybe it's a good idea. I will discuss it with our developers team.

[Lupaz]

I'm not sure what you mean by -select render element with "Color mapping" option "Off".-
Which render element has that option?
tnx

[tashko.zashev]

I'm not sure what you mean by -select render element with "Color mapping" option "Off".-
Which render element has that option?
tnx

There is a "VRayMTLSelect" render element available in the Render elements list. You can add your shader with HDR map there and uncheck the color mapping option. Then you will have separate pass for it, without any color mapping applied.

[Lupaz]

Thanks Tashko.

However, if the material you are choosing is a vraylightmtl, the option "compensate camera exposure" affects the pass. So it comes out way too bright.

If I uncheck "compensate camera exposure" I get the result I want on that render element but on the rendering itself it looks completely dark. no?

[tashko.zashev]

Thanks Tashko.

However, if the material you are choosing is a vraylightmtl, the option "compensate camera exposure" affects the pass. So it comes out way too bright.

If I uncheck "compensate camera exposure" I get the result I want on that render element but on the rendering itself it looks completely dark. no?

Yes, you are right, when the camera exposure is involved this workaround will not going to work.
If "Color mapping" option in the render element is unchecked, the exposure will not be taken into account.

In this case i can suggest to render on two passes and do it on post or to adjust the texture curve approach mentioned above.

[Lupaz]

got it. thanks.

[peterguthrie]

just bringing a very old thread here back to life.

Is there any way to do this in vray these days?

We use planes with vraylightmtl applied to it and its so hard to get the image (usually a backplate photo) looking good when you are using exponential or reinhard mapping.

Any help much appreciated

[peterguthrie]

anyone? ...