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jasen
electronics forum Guru Wannabe
Joined: 18 Jun 2006
Posts: 204
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 Posted: Mon Jul 17, 2006 10:05 am Post subject:
Re: Reduce color saturation
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aOn 2006-07-16, TSM <nonsidice@non.sidice> wrote:
| Quote: | "Bob Myers" <nospamplease@address.invalid> wrote:
Have you checked the peak levels of the video
signals these boards are producing for the same
image?
No, because they don't produce the same image. One is a Neo Geo MVS
and the other one is a Sega STV (Titan). So they are different boards.
The owner is supposed to adjust R, G & B with trimmers on the
monitor's board. But I can't open my monitor any time I want to swap
boards. So I wanted to build some circuit to alter color saturation.
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is sounds like you'd get what you want by adjusting gain and bias
(contrast and brightness) saturation is what the colour control on
a TV does.
if you're over-driving the inputs you could gea a saturation problem of
another kind - transistor saturation.
sticking some resistors in the R G abd B wires could help that,
or maybe not, it depends how radically different the two boards are.
Bye.
Jasen |
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TSM
electronics forum beginner
Joined: 16 Jul 2006
Posts: 12
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| Posted: Mon Jul 17, 2006 5:24 am Post subject:
Re: Reduce color saturation
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"Bob Myers" <nospamplease@address.invalid> wrote:
| Quote: | [...] If that doesn't
do it, you'd have to work out some way to drop the signal
levels while maintaining the right termination impedance -
which likely would require an active buffer. But try the trimpots
first - they're cheap and easy, and stand at least a fair chance
of working.
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Thank you very much for your advice, I will try the pots.
By the way... If the result should not be acceptable, wich IC would
you use as a buffer? How would you wire it? I'm worthless at
electronics, so if you could point me to some schematics I would
really appreciate it.
--
TSM |
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Bob Myers
electronics forum Guru Wannabe
Joined: 25 Jun 2005
Posts: 171
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| Posted: Mon Jul 17, 2006 4:33 am Post subject:
Re: Reduce color saturation
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"TSM" <nonsidice@non.sidice> wrote in message
news:44bab2ad.23997666@news.tin.it...
| Quote: | No, because they don't produce the same image. One is a Neo Geo MVS
and the other one is a Sega STV (Titan). So they are different boards.
The owner is supposed to adjust R, G & B with trimmers on the
monitor's board. But I can't open my monitor any time I want to swap
boards. So I wanted to build some circuit to alter color saturation.
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OK - I think I see what your problem is now. Apologies, I was
misled by the use of the word "saturation."
What you're trying to do here really ISN'T reducing the
"saturation" in the standard color use of the word; the problem
is that the cards in question don't do a very good job of
keeping their video signals within standard levels, and they
need you to adjust the video amp gains in the monitor as a
result (or else the cards are likely to overdrive the video
amp and produce the problem you're seeing). If the sync
signals are separate, you MIGHT try simply sticking some
series resistance in the video lines to drop the level as seen
by the monitor - this will cause an impedance mismatch, but
if the signal is fairly low-frequency (and most of these old
arcade games are running at TV rates anyway, so it shouldn't
be that bad), it's not going to be that much of a problem.
Sticking a 25 to 50 ohm* variable resistance (a trimpot) in
series with each video signal, ahead of the monitor inputs
(or just before the output connections at the board) could
let you play with this and see if it helps, at least. If that doesn't
do it, you'd have to work out some way to drop the signal
levels while maintaining the right termination impedance -
which likely would require an active buffer. But try the trimpots
first - they're cheap and easy, and stand at least a fair chance
of working.
Bob M.
* - These values assume a standard 75 ohm video system. |
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TSM
electronics forum beginner
Joined: 16 Jul 2006
Posts: 12
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| Posted: Sun Jul 16, 2006 9:44 pm Post subject:
Re: Reduce color saturation
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"Bob Myers" <nospamplease@address.invalid> wrote:
| Quote: | Have you checked the peak levels of the video
signals these boards are producing for the same
image?
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No, because they don't produce the same image. One is a Neo Geo MVS
and the other one is a Sega STV (Titan). So they are different boards.
The owner is supposed to adjust R, G & B with trimmers on the
monitor's board. But I can't open my monitor any time I want to swap
boards. So I wanted to build some circuit to alter color saturation.
--
TSM |
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Bob Myers
electronics forum Guru Wannabe
Joined: 25 Jun 2005
Posts: 171
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| Posted: Sun Jul 16, 2006 9:24 pm Post subject:
Re: Reduce color saturation
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"TSM" <nonsidice@non.sidice> wrote in message
news:44ba9590.16545240@news.tin.it...
| Quote: | "Bob Myers" <nospamplease@address.invalid> wrote:
Why, by the way, do you want to do this? There
may be a simpler approach.
I have a couple of arcade boards to mess with and a Commodore monitor.
While one of the board gives a pretty balanced picture, the other one
has a problem. The colors seem too saturated. Some details can only be
seen when the screen is fading to black, so the overall appearance is
flat.
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Have you checked the peak levels of the video
signals these boards are producing for the same
image?
Bob M. |
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TSM
electronics forum beginner
Joined: 16 Jul 2006
Posts: 12
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| Posted: Sun Jul 16, 2006 7:45 pm Post subject:
Re: Reduce color saturation
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"Bob Myers" <nospamplease@address.invalid> wrote:
| Quote: | Why, by the way, do you want to do this? There
may be a simpler approach.
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I have a couple of arcade boards to mess with and a Commodore monitor.
While one of the board gives a pretty balanced picture, the other one
has a problem. The colors seem too saturated. Some details can only be
seen when the screen is fading to black, so the overall appearance is
flat.
Thanks for your help.
--
TSM |
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Bob Myers
electronics forum Guru Wannabe
Joined: 25 Jun 2005
Posts: 171
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| Posted: Sun Jul 16, 2006 7:23 pm Post subject:
Re: Reduce color saturation
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"TSM" <nonsidice@non.sidice> wrote in message
news:44ba6340.3664899@news.tin.it...
| Quote: | Hello, I want to build a circuit with trimmers to reduce the color
saturation of a signal going to a monitor. The signal is made up of
these wires: R, G, B, Sync, GND.
Do I need some IC? Are there any schematics to look at?
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Yes, you would need an IC (or more correctly,
SOME active circuit) to do this properly. The
relationship between RGB values and color
saturation across the board is not a simple one.
What you'd basically be doing is converting the
RGB levels into a Y/C representation, and then
varying the relative level of the "C" components -
and then going back to RGB again.
Why, by the way, do you want to do this? There
may be a simpler approach.
Bob M. |
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TSM
electronics forum beginner
Joined: 16 Jul 2006
Posts: 12
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| Posted: Sun Jul 16, 2006 4:03 pm Post subject:
Reduce color saturation
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Hello, I want to build a circuit with trimmers to reduce the color
saturation of a signal going to a monitor. The signal is made up of
these wires: R, G, B, Sync, GND.
Do I need some IC? Are there any schematics to look at?
Thank you
--
TSM |
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