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
might do the trick, or even just 3 100 ohm pots might work if the cable length is short
martin
Hmmm, since there is no luminance signal, just 3 color signals, it would appear to be nary impossible to do what you want. These are not
3 voltages, but time varying signals. So no matter how you set the individual levels, you cant reduce the color without reducing the overall signal.Nicht var?
Luhan
Hmm, why do you think there is no luminance? All the broadcast cameras I've used generally used RGB to the Camera control units, and they worked, then DA'd in YUV. Since video distribution in RGB sucks bigtime. CRTs tend to need RGB to drive the bits of metal that dangle in the vacuum. If you put 1V on the R channel it should show red and 0V will show not a lot. I could go on, but I'm sure Mike T will chip in
martin
I't must be possible in some way, even if you have to construct a luminance/cromanance signal in an intermediary stage, reduce the chomanance signal, and then regenerate as RGB.
Luhan
I agree that RGB>YUV> RGB is the cleanest way. Maybe one of those overcomplicated SAA71xxx series ic's from Philips would do the trick
martin
Since a saturated color represents one of RGB being very much higher or lower than the other two, you might do an experiment of putting a resistor in series with each of those lines, follower by a resistor between each of them. Something like 47 ohms in series and 470 ohms between the output side of them. If that does anything like what you are looking for, we can try to come up with a single control that does something like this, in a variable way.
Maybe something like this:
R out | _V_ R ---------|___|---------+ 100R | | G out | | | _V_ | G ---------|___|---------+ 100R | | B out | | | _V_ | B ---------|___|---------+ 100R
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
If you have only R, G & B signals, reducing luminance in the display is a simple matter of blending R, G & B together with a resistive mixer!
Once stated that way, you are obviously correct.
Luhan
Err... how? :-) What is a resistive mixer?
Thank you
-- TSM
a bit of homework for you, but you may needto buy a pack of asprin
martin
That would also reduce the brightness and contrast, since there is no luminance input.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
You still need a bit of active stuff, as a resistive mixer is a tad lossy, and will need some gain, so not really practical. But I must admit I havent done the sums in a long while I was very lucky in my video engineering epoch, the boss just said "We need this, build it", so I did, so if I needed a yuv to rgb or whatever box, I just bought it, lot quicker than diy, when you are trying to get clients in through the door
martin
If I couldn't adjust the source, I would use three variable gain video amplifiers and add an adjustable DC offset to give some control, but without a separate luminance channel it still wouldn't be perfect. Maybe some four quadrant multipliers and a 18 bit D/A convert like I used on the video gain control for the Microdyne 700 series receiver. One D/A controlled gain, and the other controlled the DC offset.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
What is the video source? If it is a computer you should be able to use the advanced settings to adjust it, or go into the setup menu in the monitor and reduce the saturation. Not all monitors allow you to adjust the video, but decent video cards do. I was using a 21 inch HP monitor recently that was quite green. I went into the advanced settings and balanced the colors there. After I used the monitor a few days I re-calibrated the color, then reset the video card to the default settings.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
Be nice to hear what the OP wants to do specifically, why he needs to reduce the saturation, there might be a different approach
martin
Notice I'm not grounding the right-hand side..
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
How are you going to maintain the 75 Ohm impedance that way?
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
LM324. ?
Been there Terminated it, this resistive stuff is shit without buffering and a modicum of gain, sorry Speff.
Time to invoke Godwins' Law maybe
martin
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