There shouldn’t be a Bayer “channel”, but the Bayer filter mosaic is an arrangement of color filters used in digital image sensors.
It should contain a pattern of 50% green, 25% red and 25% blue pixels, thus the color format would be BGGR, RGBG, GRGB, or RGGB.
In that case 4 input channels might be expected. However, your current images seem to only contain 3 channels so you would have to check, if you are really reading the RAW images in this format.