Error processing techniques for the Modified READ facsimile code

The purpose of this Technical Information Bulletin is to evaluate the relative effectiveness of four different 'error processing techniques' for the Modified READ code. The four different techniques which are investigated are listed below in order of increasing complexity of implementation: Print White (PW); Print Previous Line (PPL); Print Previous Line/White (PLW); and Normal Decode/Previous Line (NDPL). The analysis is performed by means of computer simulation. A total of 72 computer runs were performed at different combinations of CCITT test document, vertical resolution, K-factor and source of transmission errors. The performance of four candidate techniques is measured by both objective and subjective procedures. The quantitative analysis is accomplished using the Error Sensitivity Factor (ESF) which represents the average number of incorrect pels in the output document caused by a transmission error. The subjective analysis is based upon viewing actual error-contaminated images generated in the simulation process. The quantitative performance of the Print White technique was found to be significantly poorer than the other three. The ESP of the PW, under the conditions analyzed, was found to be 56.3, while the average of the other three is 46.1. The error performance of the PLW approach was found to be subjectively superior to the Print White technique and comparable to the Previous Line technique. The NDPL has superior legibility and shows promise for improved overall error performance.