CBS sequential colour rides again!

[ppppenguin]

Did you think that sequential colour and colour wheels began and ended with the the CBS system in the late 1940s? Or a brief revival for the Apollo missions?

Look at:

http://www.bookham.com/documents/ColorLocWheel.pdf

to see how colour wheels are being used in the latest TV projectors.

[Aerodyne]

Not to forget that Baird also experimented with sequential colour - before 1940, I believe, before CBS... which company by the way was using colour wheels in 1941 (according to 'John Logie Baird - a Life')
I noted with a passing interest that some types of projector use colour wheels. As I only read about them in a Jessop's catalogue there was little in the way of technical info, though they claimed that the system produced bright, pure images.
Nothing new under the sun, then.
-Tony

[Steve_McVoy]

Here is CBS field sequential color in 1941:

http://www.earlytelevision.org/life_9-22-41.html

[oldeurope]

I think brightness decreases much with this
color disc .

Darius

[Aerodyne]

On the same site, here's a page about Baird's 'Telechrome' all-electronic colour TV system:

http://www.earlytelevision.org/baird...nic_color.html

Also, elsewhere on the site, the CBS system of sequential colour is described as being used into the early 1950s. Being biased, I'm inclined to believe that Baird was ahead of anyone else at this point in time!
I do know that RCA, when developing the shadowmask tube, described Baird's telechrome as 'prior art'. Without looking into it further, though, I do not know his imaging method - what type of camera did he use? Could this have been semi-mechanical, using a colour wheel, or was this also fully electronic in operation?
Fascinating site, BTW.
-Tony

[AC/HL]

Hi Tony,
I believe Baird favoured the Farnsworth image dissector tube when he turned towards electronic transmitters. Unlike most others it scans the whole picture across the sensor rather than the sensor across the picture.
I think it worked OK, but by then the money was behind EMI.

[Aerodyne]

Hi Bill
Yes, I'm sure you are right re the Farnsworth camera for monochrome use. After taking a look again in 'John Logie Baird: a Life', I have found a diagram illustrating Baird's 600-line colour TV system of 1940. At that time he used, seemingly, an electromechanical mix: to quote the text: " A grid (raster) is traced out very rapidly by scanning beams projected from a cathode ray tube* through a rotating colour filter, blue-green** and red-orange onto the subject being televised. Reflected light is picked up by several photocells and the amplified signal is transmitted to the receiver where the picture is built up through a cathode-ray tube and projected onto a ground glass screen. A good 600 line picture was obtained by having the lines transmitted alternately in different colours (interlacing). "
* No, I don't understand it either. How bright would that spot need to be?
**Cyan, of course.
The description above is hardly a technical expose. In fact I cannot see how it could work as described. It may be typical of Baird to provide half an explanation: he was always wary of giving away his secrets.
His Telechrome tube, in both two-colour and three colour forms, formed the first single-CRT colour tube display, demonstrated to the press in 1944. Again, no mention of camera source. Perhaps he was still using a wheel.
Two-colour TV probably looked as poor as the early 'two-strip' technicolour film images. Better than nothing, but muddied and impure rendering.
I wonder, did Philo T. experiment with colour?
-Tony

[jim_beacon]

The Baird system description seems to be a flying spot slide scanner - I think it would be a little ambitious to try it with a three dimensional subject (or a least a serious burn on the scanner tube).

Jim.

[peter_scott]

Originally Posted by Aerodyne

Hi Bill
. Reflected light is picked up by several photocells and the amplified signal is transmitted to the receiver

The description above is hardly a technical expose. In fact I cannot see how it could work as described. It may be typical of Baird to provide half an explanation: he was always wary of giving away his secrets.

-Tony

I took a look at my copy of JLB A Life and it is subtly different and even more confused. The illustration shows the crt as a spotlight source projecting through a set of RGB revolving filters and spiral shutter but it also shows three photo cells each positioned differently and the text reads " The reflected light was picked up by three special multiplier photo-cells, one for each colour. "

I think the author has confused the use of several photo cells with colour separation. As I understand it the multiple photo cells were positioned in a way analogous to studio lighting e.g. a cell beneath the chin would brighten that part of the image. They had nothing to do with colour separation which was purely a time function related to the rotating filters.

Peter.

[ppppenguin]

I believe Baird favoured the Farnsworth image dissector t

This tube was always going to be of little use for TV broadcasting because it was inherently extremely insensitive. This is because it did not use image storage so it's effective exposure time was probably less than 1/1000 second. Early Emitron/iconoscope tubes were not particularly sensitive but their effective exposure time was a full field (1/50 sec in the UK) and were capable of improvement.

I think the Image Dissector found limited application in taks such as the viewing of furnaces where its simplicity and ruggedness were a virtue and lack of light was not a problem.