Color Mapping Exponential + Clamped values ?

[stilgarna]

Hello Guys,

I'm using exponential color mapping because I found the light's attenuation better than linear color mapping.

My only problem is to get unclamped value, ( Scene02.jpg), when I picket into the hemisphere's light reflection I've got a 1/1/1 value.

When I'm using linear color mapping (scene03.jpg) I've got a 15/15/15 value... I need I value for nuke (glow/glare only on value greater than 1)

How to achieve exponential color mapping base on linear render ?
I only need to apply a exponential curve on my linear render ?

I'm not a mathematical expert, so how the exponential curve looks like ?

Like this ??? :
http://upload.wikimedia.org/wikipedi...als%282%29.svg

Red, blue, black ?


Sorry, my English s*cks, hope to be clear...

Best regards...

[sv]

one option could be to do the exponential colour mapping within nuke itself.
Render out the without any colour mapping (linear 1,1) then within nuke add a colourlookup node, and recreate the exponential curve.
There were some curves vlado put up somewhere which showed what the different colormappings equated to - i'll have a search for them shortly, but basically in the colorlookup, you'll see a straight linear line from 0 to 1 - grab the 1 bezier and move it to the right until it hits 2 - this is more or less how to recreate it....

[stilgarna]

I agree...

here is the exponential curve :

http://upload.wikimedia.org/wikipedi...s/c/c6/Exp.svg


Exponential curve look like this, I was hoping to found a way to achieve it in nuke without any coding skills...

I want to achieve a real mathematical operation, not an approximative one.

Someone got a tips to achieve this ?

A nuke node or expression ?



Best regards...

[stilgarna]

Sorry for double posting but I try to render the light directly in the camera view, and i've got value : 1/1/1 with a vray sphere light with intensity value setup to 20.

So my question is : does the exponential color mapping clamping highlight values ?

Best regards...

[sv]

so this:
http://www.chaosgroup.com/forums/vbu...ighlight=graph
Look for Eric's post...

in nuke, someting similar to this:


not sure about 100% mathematical accuracy, but you do also get a lot more control doing it in real-time in post

[stilgarna]

Ok, now I see why values are clamped...

Thanks... I think I can deal with a none accurate curve...

Best regards...

[instinct]

you can use a ColorExpression to do a mathematically correct exponential lookup.

Regards,
Thorsten