Issue with curves in C4D Filter Shader?

[greymiura]

I Thought I had done this a hundred times, but when I tried to adjust a bitmap texture with the curves in the C4D Filter Shader I realized that simply activating the curve section of the Filter Shader drastically changes V-Ray's interpretation of the input texture.
In this example the filter shader with a jpg inside controls the reflection glossiness. As long as the curves are disabled you get what you'd expect. Whith the default linear 0/0 - 1/1 curves enabled the resulting value is interpreted as pure black. And as soon as you lower the intensity value just a tiny little bit, the result, although a bit different than with the box unchecked, looks correct again.
In other channels (diffuse, reflection colour, ...) the result seems to be some kind of Gamma 1/2.2 version of the original texture after enabeling the curves checkbox. And it happens with Vray bitmaps as well as C4D bitmap shaders.
May I ask you to check this on your side?

S24.111, V-Ray v5.10.22, Windows 10, 2 x XEON E5-2698 v4, GTX 1080

[aleksandar.kasabov]

Hello greymiura,

I managed to reproduce this issue and have now reported it to our developers (bug ID:VC4D-1122). I will let you know once we have updates on the matter. Until then, as a workaround, you could load the C4D filter shader inside a VRayC4DBake texture. Thanks.

[aleksandar.kasabov]

Hello greymiura,

Please note that the issue reflection glossiness map was recently fixed and the fix can be found in the latest stable builds. You can get the latest one from here.

The reason for the difference in the look of the texture, once the Gradation Curves are enabled, is that the default interpolation type (spline) for the curves is currently unsupported. To get the same result with the gradation curves enabled and disabled, you will need to set the interpolation of all curves and knots to linear. Please note that both the RGB and individual R, G and B curves need to be linear to achieve the same result. I will let you know once we add support for the spline interpolation in the Filter shader.

[greymiura]

Hey Aleksandar,

great, thanks for your efforts! That was fast...

And it's good to know that only the linear interpolation is supported yet. I tried a few times to lighten up the midtones with the spline mode and was always wondering why that didn't translate in the rendering

Have a nice day!