Aperture: Unexpected results when working with grayscale or other non-RGB images
Aperture 2.x, Aperture 3.x
Adjustments on grayscale images sometimes give unexpected results, or do not work at all.
Aperture is designed to work with images from digital cameras which use an RGB color space. Non RGB images, such as grayscale TIFFs, grayscale PNGs, or RGB-A images (with alpha transparency) may not render correctly.