Sstv Camera

Fig. 3. Alignment method used in televising process.,

It is possible, with some SSTV imaging systems, to do direct color separation with the SSTV camera. Slow-scan systems employing 931A photomultiplier tubes (Mutton. 1^68) or conventional vidicons such as the 6326 (Taggart, 1968: Mutton, I96c>) have spectral response functions suitable for use in direct color separation (Cohen and Parr; 73, Jan. 1970). Slow-scan vidicon tubes, however, peak in the blue-violet, and cameras employing these tubes (Macdonald, 1965) can not be used for direct color analysis- As a camera employing a WL-7 290 vidicon was used in the present work, it was necessary to perform the color separation by photographic means.

Color Synthesis

The separation pictures were displayed on a 3 in. hybrid monitor employing a 3RP7A cathode-ray tube (CRT). The Polaroid HOB camera* now loaded with type 48 Polacolor film (ASA 75), was rigidly fixed in front of the monitor. To minimize relative camera-monitor move-

merit, the camera shutter was not used, and a black card placed before the lens between exposures. All work was done in a completely darkened room. No changes in monitor control settings were made bet wee n a given set of time exposures. Some experimentation with exposure time was necessary to produce an acceptable Polacolor print. The direction such experimentation took was influenced by careful analysis of preceding exposures. For the type CRT and film used, we found it necessary to photograph ft frames of each separation picture, through its respective filter, at an f/stop setting of 4.7. The room temperature, 7 5°F, dictated a developing time of 60 seconds.

Results & Conclusions

We have demonstrated a method for quickly and economically analyzing and synthesizing a color picture. At most, two photographic steps are required, both of which can involve the use of Polaroid quick-processing film. Careful attention must be given to insure registration of the black-and-white separation prints. However, by exercising care, amateurs should

Fig. 4. Synthesized color subject.

now be able to use this method to transmit color information by slow-scan television.

the synthesis of the color subject is shown in Fig. 4. This picture was obtained on the third try. To the extent that the color in the reconstructed picture matches the color of the original subject and the color chips, we classify the picture quality as "good/'

Acknowledgment

We thank D.J. Holscher, Hughes Aircraft Company, "ulver City. California, for supplying a copy of D.R. Davies' report. Subject photo courtesy VAR1G Airline,

References

1.Cohen. f.J, and WX. ' arr, Slow-Scan Color Transmission, 73, January* i 970,

2. Davies, D.R. Color Photography Using Surveyor Television, Hughes Aircraft Company, Culver City, California, 17 November 1964,

3. Mutton, L.I. A Slow-Scan TV Picture Generator, 73, October 1967.

4. Mutton, L.L A Fast-Scan Vidicon in the Slow-Scan TV Camera, 73, February 1969.

5. Macdonald, CM A Slow-Scan Vidicon Camera, QST> June, .lulj\ and August, 1965.

6. Taggart, R.E. Slow-Scan with Regular Vidicons, in. Technical Correspondence, QST, December, 1968.

Additional information on the transmission of color pictures by SSTV, and I heir reconstruction by additive synthesis, is to be found in an article by R.E. Taggart, 73, November, 1969.

Slow-Scan Television

Journals

Macdonald, C, "A New Narrow-Band Image Transmission System/1 QS T, August and September, 1958. Macdonald, C., "Slow-Scan Image Transmission: A Progress Report/' QST, April, 1960. Macdonald, C., "S.C.FM. - An Improved System for Slow-Scan image Transmission/' QST, Jjnuary and February, 1961.

Plowman, J.AM Slow-Scan Picture Transmission* The British Amateur Television r

Club, London, 196L Macdonald, Cs "A Compact Slow-Scan TV

Monitor/* QST> March, 1964. Macdonald, C,, "A Slow-Scan Vidicon Camera," QST, June, July, and August,

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