A method for image decoding, comprising: generating a reconstructed image, wherein generating the reconstructed image includes generating the reconstructed image using alpha channel prediction, wherein generating the reconstructed image using alpha channel prediction includes: obtaining reconstructed color channel values for a current pixel of the current image expressed with reference to a first color space; obtaining color space converted color channel values for the current pixel by converting the reconstructed color channel values to a second color space; obtaining an alpha channel lower bound for an alpha channel value for the current pixel using the color space converted color channel values; generating a candidate predicted alpha value for the current pixel; obtaining an adjusted predicted alpha value for the current pixel using the candidate predicted alpha value and the alpha channel lower bound; obtaining a decoded residual alpha value and generating a reconstructed alpha value for the current pixel as a sum of the adjusted predicted alpha value and the decoded residual alpha value; generating a reconstructed pixel for the current pixel using the reconstructed alpha value; and including the reconstructed pixel in the reconstructed image; and outputting the reconstructed image. generating a reconstructed image, wherein generating the reconstructed image includes generating the reconstructed image using alpha channel prediction, wherein generating the reconstructed image using alpha channel prediction includes: obtaining reconstructed color channel values for a current pixel of the current image expressed with reference to a first color space; obtaining color space converted color channel values for the current pixel by converting the reconstructed color channel values to a second color space; obtaining an alpha channel lower bound for an alpha channel value for the current pixel using the color space converted color channel values; generating a candidate predicted alpha value for the current pixel; obtaining an adjusted predicted alpha value for the current pixel using the candidate predicted alpha value and the alpha channel lower bound; obtaining a decoded residual alpha value and generating a reconstructed alpha value for the current pixel as a sum of the adjusted predicted alpha value and the decoded residual alpha value; generating a reconstructed pixel for the current pixel using the reconstructed alpha value; and including the reconstructed pixel in the reconstructed image; and obtaining reconstructed color channel values for a current pixel of the current image expressed with reference to a first color space; obtaining color space converted color channel values for the current pixel by converting the reconstructed color channel values to a second color space; obtaining an alpha channel lower bound for an alpha channel value for the current pixel using the color space converted color channel values; generating a candidate predicted alpha value for the current pixel; obtaining an adjusted predicted alpha value for the current pixel using the candidate predicted alpha value and the alpha channel lower bound; obtaining a decoded residual alpha value and generating a reconstructed alpha value for the current pixel as a sum of the adjusted predicted alpha value and the decoded residual alpha value; generating a reconstructed pixel for the current pixel using the reconstructed alpha value; and including the reconstructed pixel in the reconstructed image; and outputting the reconstructed image.