Applicability of a standardized discrete cosine transform coding method to character images

The Joint Photographic Experts Group (JPEG) baseline system, which is scheduled to be standardized in 1992, is applied to character images, and the characteristics of the application are investigated. The JPEG system is suitable for continuous-tone images, however, continuous-tone images are usually accompanied by characters. The image quality of characters is investigated on various magnitudes of quantization tables and the deterioration mechanisms are discussed. A method of image quality improvement that is accomplished by density transformation after decoding is proposed and its effects are confirmed.