topic Re: Bitmap Output Amount, Offset, RGB Level and Premultiplied Alpha in 3ds Max Programming Forum

Bitmap Output Amount, Offset, RGB Level and Premultiplied Alpha

robert3dsmax — Mon, 16 Jan 2017 13:32:43 GMT

Dear all,

I am tearing my hairs out trying to figure out how the Bitmap Operators work. I want to create them in a hlsl shader and try to figure out how it works:

Here is what I have got for Output, Offset and rgb Level:

Bitmap.rgb *= rgbLevel; 
Bitmap.rgb = clamp(Bitmap.rgb + offset * Bitmap.a, 0, 1);
Bitmap.rgba = Bitmap.rgba * outputAmount;

The Output amount seams not to be correct, the Color is different from the Max material.

Does anybody know where I can find the resources how 3dsmax treats the Bitmap internally?

Thank you much

Robert

Re: Bitmap Output Amount, Offset, RGB Level and Premultiplied Alpha

Anonymous — Mon, 16 Jan 2017 19:53:45 GMT

Is the output of your shader just darker/brighter than the Max material? Then you'll probably need to do gamma correction.

float gamma = 2.2;
Bitmap.rgb = pow(Bitmap.rgb, vec3(1.0/gamma));

Re: Bitmap Output Amount, Offset, RGB Level and Premultiplied Alpha

robert3dsmax — Mon, 19 Mar 2018 16:41:42 GMT

Thank you for your answer and my very late reply. I fixed it that time (I hope), the order is important as well:

//rgbLevel:

bitmap.rgb = bitmap.rgb * rgbLevel;

//offset:

bitmap.rgb = bitmap.rgb + offset * bitmap.a;

//outputAmount:

bitmap.rgba = bitmap.rgba * outputAmount;

//inbetween clamp:

bitmap.rgba = clamp(bitmap.rgba, 0.0, 1.0);

//invert
bitmap.rgb = 1.0 - bitmap.rgb;
//clamp
bitmap.rgba = clamp(bitmap.rgba, 0, 1);
//alpha from rgb Amount
bitmap.a = (bitmap.r + bitmap.g + bitmap.b) / 3.0;