The present invention relates generally to color image processing. One claim recites a method of color masking an image or video including: reading color values of an image sample of the image or video and a corresponding change of an attribute of the image sample; and based on the color values of the image sample, and using a programmed electronic processor, mapping the change in the image sample attribute to a change in color components of the image sample that is equivalent to the change in the image sample attribute, yet reduces visibility of the change in the image sample attribute for the specific color values of the image sample. Another claim recites a method including: obtaining data representing digital imagery or video; analyzing at least a portion of the data to determine one or more color characteristics associated with the at least a portion of the data, said act of analyzing yielding a result; based at least in part on the result, generating a key; and using a programmed electronic processor, embedding auxiliary data in the data representing digital imagery or video using the key. Of course other claims and combinations are provided as well.