Hello everyone. I guess I need to check this board more often
Quite a few questions have been raised about the CBS format and my converter. First the question of color fringing:
Color fringing is visible on the operating CBS sets using the converter, just to a lesser extent than would have been apparent originally. In the CBS system, a complete color image is made up of 6 fields repeated as RBGRBG. (Since it still used interlaced scanning, it required two sets of RBG sequences to make up the entire color frame since each color had to appear in both fields.) In the original system, if an object moved in any direction horizontally or vertically, it's component colors would separate. The amount of separation is proportional to the speed the object moves relative to the scanning speed in that direction across the 6 fields. In this system, each of the 6 fields could be temporally different from the previous one, and since each field represented a different color, color fringing would occur.
Since we are converting from NTSC which contains 2 fields for each color frame, only 2 groups of 3 fields in the converter output can be temporally different per frame. While this tends to decrease the number of fields that appear different, the time difference between the 2 fields in the NTSC input is greater than the difference between two fields in the CBS system making this worse.
To sum it up, because of the nature of the NTSC input, and the frame rate conversion, there is less color fringing in the output of the converter than what would have been observed originally, the field sequential source being the main difference.
As a side note, the converter performs a trick that senses if the original NTSC video came from a progressive source like a telecined movie, in which case it reconstructs the original 24fps progressive movie, which exactly matches the CBS frame rate, so no color fringing appears at all.
Of course none of this addresses the issue of darting your eyes around or moving an object quickly across the screen and seeing the color image break apart. This is inherent in any field sequential system, and is the same today using the converter as it would have been originally. I think this is the effect that most folks noticed when viewing these sets last year.
As for this being a viable option for color, keep in mind that while the frame rate was low on the CBS system to keep the bandwidth down, the field rate was at 144Hz. Compare this to most state-of-the-art single chip DLP projectors that use 4X (120Hz) or some that use 5X (150Hz) field rates. While the DLP projectors have the advantage of coming from non-field sequential sources, they will appear similar to what the CBS system would have looked like.
Someone mentioned the flicker difference between the CBS and ColorTel demonstrations last year. Remember that the CBS system while using a low 24Hz frame rate gave a complete color image at this rate. (actually your eye perceives a complete color image at 48Hz with the CBS system) while the ColorTel converter uses 6 NTSC fields to make a color frame at a 5 Hz rate. (similarly your eye will perceive a 10Hz rate with the ColorTel) This is why the CBS is basically flicker free while the ColorTel has objectionable flicker.
On the converter it self, only a composite and S-Video input were provided. As Steve McVoy mentioned, one of the downsides to the CBS system was it's relatively low bandwidth. The composite input is nice as it connects to just about anything, and the S-Video input is a component format, with the same Y bandwidth as a full YUV input, but with just somewhat less color bandwidth. Because the cost and size of the unit would have gone up with the addition of a YUV input, and the additional color bandwidth would not have been realized, it was decided to leave this off.
Hope this wasn't too long and boring of a post
Darryl