Colour mapping

[Guest]

It is my understanding that each colour mapping option adjusts the exposure and gamma of the image in a slightly different way. First, is this correct? And second, is there a formula or algorithm for each?

As a blue sky example and in no means correct, does Reinhard lower the exposure but changes the gamma to 1.8?

[glorybound]

Type - this is the type of transformation used. These are the possible types:

Linear multiply - this mode will simply multiply the final image colors based on their brightness are. Color components that are too bright (above 1.0 or 255) will be clipped. This can result in burnt out spots near bright light sources.

Exponential - this mode will saturate the colors based on their brightness. This can be useful to prevent burn-outs in very bright areas (for example around light sources etc). This mode will not clip bright colors, but will instead saturate them.

HSV exponential - this mode is very similar to the Exponential mode, but it will preserve the color hue and saturation, instead of washing out the color towards white.

Intensity exponential - this mode is similar to the Exponential one, but it will preserve the ratio of the RGB color components and will only affect the intensity of the colors.

Gamma correction - this mode applies a gamma curve to the colors. In this case, the Dark multiplier is a general multiplier for the colors before they are gamma-corrected. The Bright multiplier is the inverse of the gamma value (f.e. for gamma 2.2, the Bright multiplier must be 0.4545).

Intensity gamma - this mode applies a gamma curve to the intensity of the colors, instead of each channel (r/g/b) independently.

Reinhard - this mode is a blend between exponential-style color mapping and linear mapping. If the Burn value is 1.0, the result is linear color mapping and if the Burn value is 0.0, the result is exponential-style mapping.

[Guest]

I have read the above before, I just wondered if there was a mathematical equation for each. So for example if my scene was set up to be gamma 2.2, then I used Reinhard. what would my resulting gamma be?

[glorybound]

This thread might help you
http://www.chaosgroup.com/forums/vbu...Colour+mapping

[Guest]

Interesting, so do you think it possible to render in linear space and then apply the colour mapping in Photoshop?

[JeffG2]

You can create your own Reinhard curve in the VRay framebuffer.

[samuel_bubat]

Interesting, so do you think it possible to render in linear space and then apply the colour mapping in Photoshop?

I don´t know about photoshop, but i did this with Digital Fusion and it works well. Also this is what I would call a real linear workflow.
You would render the image out without any exposure (especially no physical camera exposure) and do all the exposure/color correction afterwards.
http://sorceress.netfrag.org/optix/_Post_Exposure.jpg
This is a test I did several years ago.

Next to that I´m a big fan of Reinhard Tonemapping. It´s pretty easy to get a decent exposure, especially in rooms with small windows.
You can get them as bright as you want without color bleeding and without harming any system Gamma values
(wich i still believe is utter nonsense the way most people use it ).
Also you don´t need to mess around with Realworld Camera Exposure settings wich are pretty limited and make no real sense at all unless
you have pyhsically correct reflectance/transmitance values for each of your materials.