Background Color Support for RGB Point Clouds

[jasonyzhang]

🚀 Feature

Hi,

The AlphaCompositor and NormWeightedCompositor currently only apply the background color if the point cloud is RGBA rather than RGB. However, the _add_background_color_to_images actually works fine whether the pointcloud is RGB or RGBA.

The current code does not apply the background color for RGB point clouds, explicitly checking for an alpha channel:

pytorch3d/pytorch3d/renderer/points/compositor.py

Lines 37 to 39 in 9e2bc3a

	# check for background color & feature size C (C=4 indicates rgba)
	if background_color is not None and images.shape[1] == 4:
	return _add_background_color_to_images(fragments, images, background_color)

pytorch3d/pytorch3d/renderer/points/compositor.py

Lines 59 to 61 in 9e2bc3a

	# check for background color & feature size C (C=4 indicates rgba)
	if background_color is not None and images.shape[1] == 4:
	return _add_background_color_to_images(fragments, images, background_color)

Is there a specific rationale for this? I have tested setting images.shape[1] == 4 to images.shape[1] in (3, 4), and the output is as expected.

Thanks in advance!

[nikhilaravi]

Thanks for pointing this out! We will update this function to work for both RGB and RGBA.