Enhancement of colored engravings

Digitization of printed illustrations for archive purposes is not always a simple procedure. For example, colored engravings (a common book-illustration type of the XVIII and XIX century) consist of regions of both very fine lines and almost uniformly colored regions. In order to keep the compression rate high, compression algorithms tend to destroy fine lines (the high-frequency content) that are the essence of this type of image. However, the images compressed using the modified mixed raster content (mMRC) compression scheme retain the lines and show exceptional fidelity to their prototypes at low bit-rates when compared to alternate compression methods such as JPEG and JPEG2000. This paper presents the simple algorithm for data-filling of the MRC background layer, that improves the compression results, and - at the same time - enhances the reconstructed image. This is demonstrated on the case study of the colored engravings from the William Blake Archive.