ImageMagick: Magick::Image Class

ChannelType layer_ Extract channel from image. Use this option to extract a particular channel from the image. alphaChannel for example, is useful for extracting the opacity values from an image. / const std::string &comment_ Comment image (add comment string to image). By default, each image is commented with its file name. Use this method to assign a specific comment to the image. Optionally you can include the image filename, type, width, height, or other image attributes by embedding special format characters.