[mythtv-users] Image quality, what effects it?

Gert van der Knokke gertk at xs4all.nl
Mon Aug 9 07:05:07 EDT 2004

Terrence Martin wrote:

> So I have my mythtv set up, insofar as it records properly.
> However I am not happy as yet with the output, neither livetv nor 
> recorded programs.
> The image seems grainy. Now currently I am attributing this mostly to 
> the WinTV bt8x8 that I am using. Once my PVR250 arrives I will know 
> better where I stand.  In particular the color is a bit washed out. 
> Even with a filter. I understand the bt8x8 are known for this.

You can adjust color, brightness, hue and contrast on all BT8x8 cards. 
Try playing with them,  starting from the 'middle' position. you can 
easily do this from Xawtv for checking.

> I have a couple more questions though...
> Is there a quality difference between svideo and composite?

Hmm, not sure what you mean by this since you are using the antenna/coax 
input for your cable signal I assume, so I guss you mean output from the 
computer to the TV. S-Video has separated video (Y) and color (C)  
signals so quality should be better than  composite (CVBS) .

> How much effect does the cable quality have on the output?

Very much effect... Use double-shielded coax in all connections since 
your computer is a major source of radio signals which interfere with 
the cable signals resulting in all kinds of stripes, patterns, spots..

> What kind of vertical and horizontal refresh do people find a standard 
> analog TV can do?  Specifically does anyone know what a sony trinitron 
> 32 inch KV32S42 do?

All standard TV's handle the same (input) refresh rate that is: 60 Hz 
for NTSC and 50 Hz for PAL sets, some of them handle both 
(multistandard). Note: this has nothing to with the fact that there are 
so called 100 Hz TV-sets, the output framerate is created/converted 
inside the set, input framerate will always be 50 or 60 Hz since it must 
comply to the NTSC or PAL standard. PAL and NTSC have a line frequency 
(horizontal rate) of about 15 KHz.
You will notice improvement if your output videocard can do interlaced 
output, this will effectively double you vertical resolution. The 
horizontal resolution  is not really  a standard since the signal always 
was analog, you can use the typical DVD  'standard' of 720 pixels per 
line. Remember however, the higher the horizontal resolution, the more 
work your computer has to do.

> I am thinking I want to switch from svideo to composite out, for the 
> primary reason that if I do that I can use my reciever (svideo 
> overides my Sony Trinitrons composite video in).  Of course only if I 
> do not loose quality as a result.
This will decrease the quality a bit, most notably in things like 
(diagonal) stripe patterns (for instance a newsreader with a striped 
suit or tie) for the rest you probably won't notice the difference.
Just use a proper (75 ohm coax) cable for the composite output to your 
TV set (do not use an audio cable).


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