The sound of phonographic records is contained in the radial position of the groove (and sometimes also its depth). The sound is usually extracted by a mechanical device (the stylus of the record player). Many old records are in such bad shape that no mechanical contact is possible. An alternative is to take a picture of the record and to estimate the radial groove position, using image processing. In this paper, we present the technique to extract the radial position of the groove and therefore the sound of the records.

The optical retrieval and storage technique called VisualAudio provides a way to extract sound information from an analog disk without any mechanical contact. The process is straightforward: we take a picture of each side of the disk using a dedicated analog camera, we store the film as our working copy, and when needed, we scan the film and process the image in order to extract the sound. This technique can be used to retrieve the sound from old records that are in such a bad shape that no regular turntable can be used. A working prototype has been built and has retrieved the sound from several records. We present the signal processing issues of this system and, in particular, a signal-to-noise ratio analysis.

A technique is proposed for transmitting two-tone images in a progression of stages. In the first stage, information is transmitted to allow a crude reproduction of the picture. In the following stages, the quality of the received picture is improved until a copy identical to the original is obtained. The proposed technique uses a modification of the two-dimensional code recommended by the CCITT for transmission of facsimile. The main features of the coding scheme are as follows. 1) A crude version of the image is obtained after approximately 10-20 percent of the total transmission time. A good version, with half the resolution in both the horizontal and vertical directions, is obtained after 50 percent of the total transmission time. 2) Compatibility with the CCITT codes for transmission of facsimile. 3) Total transmission time is only about 20 percent larger than the time required for nonprogressive transmission using the CCITT codes.

Some properties of Huffman codes are presented. It is shown that knowing the probabilityP_{1}of the most likely source letter, there exist new lower and upper bounds on the redundancy of the Huffman code which are tighter forP_{1} \geq 0.4than those given by Shannon's first theorem or by the more recent results of Gallager. It is also shown that the new bounds are the tightest possible forP_{1} \geq 0.4when it is supposed that PI is the only known probability.