1. A computer-implemented method comprising execution, by a processor, of operations including: obtaining, from a memory, an a×b pixel macro-cell from a digital image that contains 4 non-overlapping m×n pixel cells, wherein pixels in the a×b pixel macro-cell have respective pixel values and are associated with respective tags; determining that less than e of the respective tags indicate that their associated pixels represent edges in the digital image, wherein e is at least 1; based on less than e of the respective tags indicating that their associated pixels represent edges, and ranges of pixel values in each of the 4 non-overlapping m×n pixel cells, selecting a compression technique, wherein selecting the compression technique comprises (i) determining that the ranges of pixel values in each of the 4 non-overlapping m×n pixel cells are less than or equal to a non-zero threshold value, (ii) determining respective average pixel values for each of the 4 non-overlapping m×n pixel cells, and (iii) determining that either (a) at least one of the ranges of pixel values is greater than a cell-level threshold value, or (b) a range of the respective average pixel values is greater than or equal to a macro-cell-level threshold value; applying the selected compression technique to the a×b pixel macro-cell to form a compressed representation of the a×b pixel macro-cell, wherein applying the selected compression technique comprises: (i) downsampling blocks of pixels in the a×b pixel macro-cell to a downsampled m×n pixel cell, wherein the downsampling does not consider whether pixels in the a×b pixel macro-cells represent edges in the digital image, and (ii) encoding a transform of the downsampled m×n pixel cell; and storing, in the memory, the compressed representation of the a×b pixel macro-cell.