1. A method for coding information for prosthetic visual presentation, the method comprising: sequentially selecting portions of an image; and for each selected portion, forming a plurality of values to represent the portion, and forming signals for presentation of the plurality of values representing the portion of the image on corresponding electrodes, including forming signals for sequential presentation of a plurality of disjoint subsets of the values in corresponding successive time intervals; wherein the image is represented as a plurality of scan lines of pixels, and each selected portion includes a corresponding subset of the scan lines of the image; and wherein forming the plurality of values to represent the selected portion of the image includes forming a plurality of blocks of pixels in the subset of scan lines, and forming a transform representation of each of the blocks of pixels.