A transformation system for increasing the compressibility of digital images. In one embodiment, the pixels of a digital image are examined, one at a time. The color of the examined pixel is compared to that of its neighbors. If the difference in color from either of the neighboring pixels is below a threshold, the color of the neighbor that is closer to the color of the examined pixel is copied to the examined pixel. If neither of the neighbors is close enough in color, the color of the examined pixel is unchanged. The pixels are examined in a single pass. After each pixel has been examined, and possibly changed, the compressibility of the image using a dictionary-based technique, such as one of the Lempel-Ziv techniques, is typically improved.