Render Color Equation

[saptarshi1234]

kaolin-wisp/wisp/tracers/packed_rf_tracer.py

Lines 148 to 153 in cb47e10

	# Populate the background
	if bg_color == 'white':
	color = (1.0-alpha) + ray_colors
	else:
	color = alpha * ray_colors
	rgb[ridx_hit] = color

I have a doubt in this section of the code.
When the background is white what is the interpretation of adding "ray_colors" to "(1-alpha)"?
Will this not make the value of "color" to more than 1?

[orperel]

White background assumes the image was created with premultiplied alphas:
https://microsoft.github.io/Win2D/WinUI3/html/PremultipliedAlpha.htm

Specifically:
result = source.RGB + (dest.RGB * (1 - source.A))
but here dest.RGB is simply 1.0 due to white background.

This is only true if the data is compatible, and indeed the NeRFSyntheticDataset applies this fix, see here:
https://github.com/NVIDIAGameWorks/kaolin-wisp/blob/main/wisp/datasets/formats/nerf_standard_dataset.py#L426-L428

Are you seeing any bug here?
Thinking out loud here - maybe it makes sense to separate this param to actual "bg color" and "is_premultiplied_alphas"