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Discussion Starter · #1 ·
I have a Sony XBR 61 rear projection TV, about 3 years old. While DirectTV on S-Video is great, I find that both DVD players I've had so far (one Toshiba, now a Sony) have what I think is referred to as dot crawl on S-Video.


One large areas of similar color when there is movement I see sort of a "screen door" effect in that area, like there is a fine mesh that I am viewing the picture through. When there isn't movement its ok. I'm NOT referring to MPEG artifacting...


Does this sound like dot crawl? If so, is it possible that this fairly high-end TV has a better comb filter than the DVD players, which is why I don't see it on composite?


I'd like to run S-Video, but is it possible that even aside from dot crawl the composite connection will really provide a better image given a sufficiently superior comb filter in the set?


Thanks for any info... I'm currently quite bummed about the DVD image quality because of this!
 

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Poor chroma decoding usually causes 'hanging dots' which appear as small dots on the right edge of an area of solid colour. The colour inside the area is solid, though.


DVD and digital satellite should not show chroma decoding artifacts originating from the player as video is transported with the colour signal already split into separate components. (Though I have occasionally seen decoding artifacts which are due to the signal being mixed to composite and then decoded in the production chain - this isn't the fault of your player however.)


It sounds like what you're seeing is interlacing. This will always be noticeable on a large screen and is a function of the video standard itself. The only way to avoid this is to put a deinterlacer (line-doubler) into the display chain. You'd need to check if your TV can handle the higher refresh rates of a line-doubler though (it will display a full frame every 1/60th of a second instead of just half the frame every 1/60th).
 

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Well, you are not seeing dot crawl or hanging dots, and it's not an effect of a comb decoder!


Dot Crawl is seen on a transition between two significantly different colours in the horizontal direction (i.e. on vertical edges) Dot Crawl is a by-product of 'simple' composite decoders.


Hanging dots occur on a colour, or colour to no colour transition in the vertical direction ( i.e. on Horizontal edges) Hanging dots are a by-product of Comb decoders


The best decoder will adaptively switch between simple and comb decoding depending on the picture content (but they are expensive!)


These by-products are the result of separating the colour and black and white information, which is already separated in a S-Video signal.


There are two possible causes of what you see;


one is M-PEG artefacts called 'mosquito noise' which will occur in flat areas with slight movement or content changes - though you do say it's not M-PEG.


The other is that the colour information is breaking through onto the luminance part of the S-Video signal. this high frequency 'noise' will look like a rough diamon pattern across flat colour areas. This could be caused by poor screening on the cable or within the player or TV - or possibly the player is not set up correctly, some need to have the correct output selected even though they otherwise appear to work OK.


I hope this helps!


Richard Ansell


Snell & Wilcox
 

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Discussion Starter · #4 ·
It does sound like it better fits your descriptions of "mosquito noise" (does that derive from the appearance mosquito netting perhaps?) or the color information breaking into the luminance portion.


Is there a way to distinguish one from the other? I do note that that I'm seeing it even in the still image displayed by the disk player when no disc is present, which I think would rule out MPEG artifacts.


I've tried a different DVD player (no change), and I'm sure I've tried a different cable, but will repeat that. I will also try a different input on the TV. Any other tips in tracking it down and eliminating it would be very welcome!


Thanks,

Dave
 

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Discussion Starter · #5 ·
As a followup, I picked up a rudely expensive Monster S-Video cable (just the $60 one though, not the $100 one), which actually cured the problem.


I'm pretty cynical about high-dollar cables for audio, but I guess for video it paid off this time!
 
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