Ordering Techniques for Coding of Two-Tone Facsimile Pictures

Abstract

This paper describes some techniques for efficient coding of two‐tone (black and white) facsimile pictures. These techniques use the two‐dimensional correlation present in spatially close picture elements to change the relative order of transmission of elements in a scan line. This ordering increases the average length of the runs of consecutive black or white elements in the ordered line, making the data more amenable to one‐dimensional run‐length coding. We describe several variations of the ordering scheme, which differ in complexity and coding efficiency and evaluate their coding efficiency. For a variety of 8‐1/2 inch by 11‐inch typed documents, road maps, and circuit diagrams scanned with 200 lines/inch, these techniques reduce the bit rate by 30 to 50 percent over and above the one‐dimensional run‐length coding along a scan line; for single‐spaced typed material with 100 lines/inch, this reduction is about 25 percent. We compare one of our techniques with a two‐dimensional compression technique recently proposed by Preuss. We show that our technique results in an entropy about 10 to 18 percent lower than that obtainable through Preuss' technique.

Adaptation of Ordering Techniques for Facsimile Pictures with No Single Element Runs

“…6 Pictures are modified so t h a t runs of single " w h i t e " (="0") or "black" (="1") elements along a scan line a r e suppressed. A t high resolution of 200 dots/inch, such a modification does n o t degrade t h e picture signifi cantly.…”

An investigation of storage and communication codes for an electronic library

“…Reference [5] is a continuation of the work in [3] done by the same authors. It used the ordering technique that depends on the state of the pel as described in the discussion of [3]. It had the follow ing enhancements;…”

“…Reference [3] gave some techniques for using the correlation be tween pels from line to line. It did this by ordering, in a buffer, pels or error prediction of current line based on information from cur rent line and/or previous line.…”

“…3 shows that the compression factor of image doc4a is 1.96 which corresponds to a compressed image of size 8163 bytes.Figure 4.10 shows that white run-length 2 has a frequency equal to 5905. The modified Huffman table assigns a code of length 2 bits to this run.…”