Methods, apparatus and computer programs are provided for storing a set of sensor output images for multi-exposure high dynamic range processing to produce a processed image. The multi-exposure high dynamic range processing combines pixel values from one or more of the sensor output images to produce the processed image. In one example, a method comprises receiving from an image sensor a first sensor output image. The first sensor output image has a first exposure. The method also comprises receiving from the image sensor a second sensor output image. The second sensor output image has a second exposure different than the first exposure. First image pixels of the first sensor output image having pixel values which are unlikely to have a substantial contribution to the processed image are identified, and the amount of information stored in relation to the first image pixels is reduced on the basis of the identifying step.