1. A data file for storing a still image, the data file comprising: a plurality of decomposition levels representing the still image at increasingly higher levels of resolution, the decomposition levels being arranged in order of increasing levels of resolution; individual decomposition levels each comprising a plurality of subimages which allow reconstruction of an image representation of the still image, said subimages having rows of subimage values corresponding to rows of said image representation; said rows of subimage values being arranged within each particular decomposition level in row blocks, each row block containing a row of subimage values from a plurality of subimages of the particular decomposition level, wherein the rows of each row block correspond to a common image representation row.