This disclosure concerns a method for enhancing vision for a vision impaired user comprises. A processor, such as a controller of a retinal prosthesis, determines based on input image data a shape associated with an object represented by the input image data. The processor then determines for each of multiple areas of the input image data a coverage value that indicates to what extent the shape covers that area of the input image. Each of the multiple areas is associated with one of multiple imaging elements of the retinal prosthesis. The processor then determines an output value for each of the multiple imaging elements of the retinal prosthesis, such that when the output values are applied to the imaging elements to create a visual stimulus, a contrast is perceivable between a first element and a second element based on their respective coverage values.