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Some notes on VHS resolution...
I have the impression that people are often mistaking "lines" for
"pixels" when it comes to determining the optimum resolution for
video recording. I have often read in this forum that a resolution
of something like 352x288 at 25 Hz would be "identical" to VHS-PAL
resolution, or even that VHS recorders can't display more than 200
pixels per line anyway. I have even read someone stating that NTSC
is "defined" as 300x240 which is absolute rubbish. I would like to
take this opportunity to get rid of these prejudices.
The manual of my (PAL) videorecorder states that it has a
resolution of 200 lines. So it should be able to show me
roughly 200 vertical lines, that's either dark lines against
a light background or vice versa. Come to think of it, there's
a minimum of 400 PIXELS required to do that on a monitor
screen, isn't it?
Let's do a quick check to verify this. A TV has a line frequency
of 15625 Hz. VHS has a system bandwidth of 3 MHz. Therefore, in
one display line, there's room for 3000000/15625 = 192 full
wavelengths. Each wave has a crest (white) and a valley (black)
so we're actually talking about 192 lines here, which is 384
pixels. There's some overhead involved, so about 350 pixels
remain visible.
The vertical resolution is 15625/25 = 625 "pixels" interlaced at
50 Hz, of which 576 remain after subtracting overhead.
Interlacing is a "brilliant" technique used to improve smoothness
of motion, reduce flicker and increase vertical resolution by
using "half-frames" that are displayed with a slight vertical
offset.
Every VCR is capable of displaying interlaced video, so there's
no reduction in vertical resolution. My conclusion is, that
my VCR displays 350 x 576 pixels interlaced !!!
The Marvel offers you a similar resolution, 352 x 576 x 50 (i).
Non-interlaced resolutions, such as 352 x 288 x 25Hz, that
are used in programs like MediaStudio, reduce both the visual
VERTICAL resolution and the smoothness of movement by half
because instead of using two distinct half-frames, they
simply display the same frame twice. The quality you get is
visibly poorer then what a good VHS system delivers.
I'm personally convinced that even the "half-pal" resolution
352x576x50 (i) causes too much quality loss to serve as source
material for VHS copies: If the output signal of the Marvel
is comparable to VHS quality, and you copy this signal onto VHS
tape, you'll get a second-generation copy. Comparable to
copying VHS to VHS....
So I advise everybody to stick to full-resolution when it comes
to video editing!
[This message has been edited by Flying dutchman (edited 05 November 1999).]
"pixels" when it comes to determining the optimum resolution for
video recording. I have often read in this forum that a resolution
of something like 352x288 at 25 Hz would be "identical" to VHS-PAL
resolution, or even that VHS recorders can't display more than 200
pixels per line anyway. I have even read someone stating that NTSC
is "defined" as 300x240 which is absolute rubbish. I would like to
take this opportunity to get rid of these prejudices.
The manual of my (PAL) videorecorder states that it has a
resolution of 200 lines. So it should be able to show me
roughly 200 vertical lines, that's either dark lines against
a light background or vice versa. Come to think of it, there's
a minimum of 400 PIXELS required to do that on a monitor
screen, isn't it?
Let's do a quick check to verify this. A TV has a line frequency
of 15625 Hz. VHS has a system bandwidth of 3 MHz. Therefore, in
one display line, there's room for 3000000/15625 = 192 full
wavelengths. Each wave has a crest (white) and a valley (black)
so we're actually talking about 192 lines here, which is 384
pixels. There's some overhead involved, so about 350 pixels
remain visible.
The vertical resolution is 15625/25 = 625 "pixels" interlaced at
50 Hz, of which 576 remain after subtracting overhead.
Interlacing is a "brilliant" technique used to improve smoothness
of motion, reduce flicker and increase vertical resolution by
using "half-frames" that are displayed with a slight vertical
offset.
Every VCR is capable of displaying interlaced video, so there's
no reduction in vertical resolution. My conclusion is, that
my VCR displays 350 x 576 pixels interlaced !!!
The Marvel offers you a similar resolution, 352 x 576 x 50 (i).
Non-interlaced resolutions, such as 352 x 288 x 25Hz, that
are used in programs like MediaStudio, reduce both the visual
VERTICAL resolution and the smoothness of movement by half
because instead of using two distinct half-frames, they
simply display the same frame twice. The quality you get is
visibly poorer then what a good VHS system delivers.
I'm personally convinced that even the "half-pal" resolution
352x576x50 (i) causes too much quality loss to serve as source
material for VHS copies: If the output signal of the Marvel
is comparable to VHS quality, and you copy this signal onto VHS
tape, you'll get a second-generation copy. Comparable to
copying VHS to VHS....
So I advise everybody to stick to full-resolution when it comes
to video editing!
[This message has been edited by Flying dutchman (edited 05 November 1999).]
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