[Coco] Coco game engine demo

[William Astle]

On 13-02-03 05:23 PM, Harry Hurst wrote:
>> That's interesting and unexpected.  Any idea why they chose 60000/1001
>> instead of 60 fps exactly as the NTSC standard frame rate?
>>
>
> I can't find the reference book I would usually consult before addressing
> this question, but Wikipedia has a pretty good explanation.
>
> http://en.wikipedia.org/wiki/NTSC#History
>
> When the color subcarrier was added to video signal a visible interference
> was seen on the B&W screens. To get rid of it the field rate was lowered.
> It couldn't be much or the old sets wouldn't be able to sync up with it.
>
> And just to split a few hairs ;D , the actual field rate can be calculated
> by dividing the color subcarrier frequency, 3.579545 MHz, by (227.5*525),
> which is exactly 1,431,818/47,775, or ~29.97 fps. The frame rate is double
> that, at 2,863,636/47,775, or ~59.94 Hz.

To split a few more hairs, you have the terms field and frame reversed 
here. The field rate is 59.94 and the frame rate is 29.97. Though, when 
dealing with interlaced signals, one really doesn't have a true notion 
of frames since the two fields necessary to make a full frame are offset 
in time.

>
> BTW the interference pattern can still be seen at times. Try taking a
> picture of your television screen (CRT, not LCD, LED or other state of the
> art screens) and you should be able to see it, unless your camera filters
> it out, as some do.

The interference patterns can actually be used to recover colour 
information (to a greater or lesser degree) from B&W recordings of an 
NTSC colour signal, too. Having seen a before and after of such a 
process, I have to say the results do leave a bit to be desired, but it 
is impressive nonetheless.

>
> HH
>
>
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