Encoding and processing of color engravings (using MRC)

Digitization of printed illustrations for archive purposes is not always a simple procedure, due to the varied nature of illustration processes. For example, colored engravings were once the predominant type of book illustrations. Due to the specific printing process they consist of regions of both very fine lines (high-frequency) and almost uniformly colored regions (low-frequency). In order to keep the compression rate high, compression algorithms tend to destroy the fine lines that are the essence of this type of image. However, the images compressed using the modified mixed raster content (MRC) compression scheme showed 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 segmentation algorithm for fast separation of engraved and colored layers, as a part of the image processing process necessary for MRC scheme implementation. This is demonstrated on the case study of the William Blake Archive.