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How to make composite video black and white?

signalblocking

Nov 30, 2021
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How to make composite video black and white? I notice that sometimes when the wire is not fully inserted the signal is black and white.

Are there any mods I can do to make composite video signal black and white or covert it into component video signal?
 

Harald Kapp

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To convert RGB to B&W you add the red, green and blue components in varying amounts. See e.g. the equations under "Luma coding in video systems" here.
 

signalblocking

Nov 30, 2021
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To convert RGB to B&W you add the red, green and blue components in varying amounts. See e.g. the equations under "Luma coding in video systems" here.

I was looking for an already designed schematic.

Turn down the color (intensity) pot on the receiver.

Why do you want to eliminate the color?
To eliminate it in the composite signal, you would have to sharply filter out anything above about 3MHz.

Why would you want it converted to component video?

I don't have such option on the receiver. This is for regular computer use, the graphics card doesn't have that option and monitor's options to reduce RGB is not making it entirely black and white.

I want to eliminate color to avoid distractions and make it easy on my eyes.

I thought if I converted it to component video, I could remove one or two components and make it black and white, this would be less complicated than creating filter for composite video signal.
 

signalblocking

Nov 30, 2021
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Which would be easy to achieve, will it be easy to mod an HDMI connection to make it display black and white or will it be easy to mod VGA connection to make it black and white.
 

Harald Kapp

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crutschow

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I know of no ready built circuit but you could sum the 3 color signals of the VGA to make one black and white signal, and then connect that signal to the three VGA color inputs on you monitor. That should give a black and white picture.
That could possibly be done with just a simple emitter follower mixer.
What resolution is the picture?

Below is an example circuit that should do what you want, depending upon the resolution and thus frequency content of the signal.
It uses an NPN and PNP BJT to give a complimentary emitter follower circuit with near zero offset.
The input resistor values are selected to match a 75Ω coax line.
upload_2021-12-2_1-15-29.png
 
Last edited:

Tha fios agaibh

Aug 11, 2014
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Did you check to see if there's color settings for your graphics card in the control panel?

Switching to another graphics card is an option.
 

signalblocking

Nov 30, 2021
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I know of no ready built circuit but you could sum the 3 color signals of the VGA to make one black and white signal, and then connect that signal to the three VGA color inputs on you monitor. That should give a black and white picture.
That could possibly be done with just a simple emitter follower mixer.
What resolution is the picture?

Below is an example circuit that should do what you want, depending upon the resolution and thus frequency content of the signal.
It uses an NPN and PNP BJT to give a complimentary emitter follower circuit with near zero offset.
The input resistor values are selected to match a 75Ω coax line.
View attachment 53471

Thanks for this. Will it work for 1080p 60Hz?

Did you check to see if there's color settings for your graphics card in the control panel?

Switching to another graphics card is an option.

No graphics card doesn't have such option.

See this discussion for achieving B&W using windows settings.

I rather it was a hardware solution than software solution
 

AnalogKid

Jun 10, 2015
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Composite video has the color information modulated onto a 3.58 MHz subcarrier, which is added to the monochrome signal. A notch filter centered at the subcarrier frequency will attenuate it and some of its harmonics, but it also will attenuate the high frequency part of the monochrome signal, removing some sharpness detail from the image.

The "right" way to remove the color subcarrier is with a comb filter. This is a form of notch filter that removes the notch frequency (3.579545 MHz) plus its harmonics and sub-harmonics. In the time domain, the attenuation curve looks like a series of dips, like the teeth of a comb. In the frequency domain, the filter attenuation peaks are interleaved with the monochrome video's major energy bands centered on multiples of the horizontal line frequency. No filter is perfect, but this way the color removal is better and the monochrome degradation is less than with a simple notch filter. BTW that interleave is part of the reason the color subcarrier frequency is such a weird value.

Older analog gear did this with a filter plus a short delay line, but today's equipment does this in a digital signal processor chip with lotsa math. Analog video is a messy business. Not trying to overload you, but here is a page that covers how and why it is constructed.

http://what-when-how.com/display-in...-part-i-television-display-interfaces-part-1/

ak
 
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signalblocking

Nov 30, 2021
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I know of no ready built circuit but you could sum the 3 color signals of the VGA to make one black and white signal, and then connect that signal to the three VGA color inputs on you monitor. That should give a black and white picture.
That could possibly be done with just a simple emitter follower mixer.
What resolution is the picture?

Below is an example circuit that should do what you want, depending upon the resolution and thus frequency content of the signal.
It uses an NPN and PNP BJT to give a complimentary emitter follower circuit with near zero offset.
The input resistor values are selected to match a 75Ω coax line.
View attachment 53471

What is +5v(battery?)and for ground can I use the ground found on VGA socket? Instead of adding resistors and transistors, what happens if I just combine the RGB outputs into one and from that I take 3 separate outputs for RGB? The combine signal would be black & white, I think, would it achieve the same effect?
 

AnalogKid

Jun 10, 2015
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Same effect, yes. B.U.T . . .

Analog video runs around on controlled impedance coaxial cables for a reason. The reason is a butt-load of math, but the problem is the termination resistors at each end of the signal path, and the quality(?) of the VGA driver circuit. There probably is a 75 ohm resistor in series with each VGA output signal, and another 75 ohm resistor to GND at each VGA signal input in the monitor.

Shorting everything together in the middle means that each output driver now is driving a much lower impedance. Looking outward, each signal driver will "see" its own output terminator plus *five* other terminators in parallel, for a combined impedance of 90 ohms; not just one terminator at each end for an impedance of 150 ohms.

Might work, *probably* will not destroy the chips in the output circuit, but no warranties expressed or implied.

ak
 
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