Does this supports RGB buffer for input?

[masterq32]

Does this supports RGB buffer for input?

[MasterQ32]

This implementation operates not on a byte array, but always on a Color array which is an RGBA value. But if you serialize an image with all alpha bytes as fully opaque, it is serialized as RGB.

Note that this doen't matter at all, as QOI only can encode RGBA images anyways, the file header value is purely informational

[wx257osn2]

This implementation operates not on a byte array, but always on a Color array which is an RGBA value.

OK, so we need to convert a 3-channel packed pixel byte array to a Color array by adding fully opaque alpha channels before encoding, right?

as QOI only can encode RGBA images anyways, the file header value is purely informational

Your point also make sense; the reference implementation always handles 4-channel pixels, but just doesn't touch the alpha when channels == 3.
However, at least the reference can encode the byte array which contains a 3-channel packed pixel image directly according to the channels.
IMO that is an overstatement from this point of view.