Grey Card Test

[LFedit]

Hey guys, a seemingly easy test is proving to be more difficult than expected. Make a 127,127,127 sRGB matte surface render out as 127,127,127 sRGB value in Photoshop. When either using linear or sRGB color management, or using linear response curve and white balance. The render always varies in a somewhat predictable manner. It always render a bit green, and also shifts more green the less light there is and less green the more light there is.

My test is a 127,127,127 matte material on a cube primitive. Use a black body emitter with 6500k. And render to sRGB through the render cue. Is it possible in this simple of a test to render a luminance shift only and not a hue shift? I've also tried using the normalized black body emitter and still get a hue shift that is always lean a bit greener than neutral.

any help is appreciated. I've read through the linear section of the manual and postings here in the forums, but getting color cast is a bit different than a gamma curve issue. Any thoughts on a how to sorting this out?

thanks,

LFedit.

[roeland]

It's a bit greenish because the tone mapping uses a slightly different white point than sRGB. Our white point is chosen to have an environment with an RGB color of (1, 1, 1) rendered as neutral grey. If you need D65 to be rendered as neutral grey you can change the white point in the imager settings to (0.754, 0.958, 1.000).

--
Roeland

[LFedit]

Thanks for the response roeland,

When going to the white point setting in the imager in C4d, from what I can tell we can only input RGB numbers (whole numbers) not decimal/linear numbers. Am I missing something when inputting this white point compensation? Also, do you have a list of white point compensation for the traditional photography lighting. 3200 Tungsten and 5600 Daylight? As i'm assuming this compensation for D65 is not going to be relative as we change color temperature warmer and cooler in Octane. Thanks again.

[zackyd]

Click on the small arrow on the left hand side of the color picker to drop down various ways of displaying the values.

[LFedit]

Thanks zackyd, using the suggested numbers in the RGB 0%-100% as a white point, it shift the output image really red. I think i'm missing how to input the correct data to compensate. Using a tone mapped or linear output from Octane still shifts from neutral. Thanks for the help.

[aoktar]

Thanks zackyd, using the suggested numbers in the RGB 0%-100% as a white point, it shift the output image really red. I think i'm missing how to input the correct data to compensate. Using a tone mapped or linear output from Octane still shifts from neutral. Thanks for the help.

Try to use the color control of diffuse on octane material to see corrected values

[LFedit]

Thanks Aoktar, doing that in the diffuse material makes a very Cyan color in the render. Any other ideas? Am I doing it wrong?

[aoktar]

can you put your scene here to check it

[LFedit]

thanks for taking a look, this is just a really simple test i'm trying to apply the concept to a product rendering. But if I can't get this simple test to be neutral and understand how to do it I can't really move forward with the product rendering. Also notice how the hue of the lighter side leans green, and the shadows lean more yellow. As always Aoktar you're doing an awesome job with the plug-in and I love using it!

https://www.hightail.com/download/ZUcyN ... MUJ3SGNUQw

[aoktar]

well, Roeland is right. This is my result with blueish white balance and linear camera response. I changed to arealights for getting faster results. Also i converted standart material to octane. Because it was giving wrong colors due srgb. Scene color profile has been changed to Linear