Abstract: Imagery data is compressed by subdividing the data into a plurality of blocks. Each block is encoded into a bit map and a pair of threshold values. The bit map provides an array of binary encoded imagery data-representative vector combinations. A vector combination is subdivided into a set of adjacent sub-blocks, each which is examined to determine whether or not it is associated with a prescribed attribute of the image. If the vector is associated with a prescribed attribute, a code representative of that attribute is generated. If the vector is not associated with a prescribed attribute of the image, prescribed portions of the vector are inverted to derive modified vectors that are associated with prescribed image attributes. For each such modified vector a corresponding code is generated. Using each of these corresponding codes, image data is effectively reconstructed and then compared with the original image data.