Electronics > Projects, Designs, and Technical Stuff
Amplifying Color Carrier (Saturation) on CVBS signal.
(1/1)
syntax333:
Hi, I want to amplify only the saturation part of the CVBS signal as shown in attachment.
Is there a circuit for this purpose only? or do I have to first high pass the CVBS then amplify and somehow add to the original signal?
Benta:
Never heard of this demand before, and I'm convinced there's no IC available. This would normally be done by demodulating to RGB and doing colour processing from there.
Can you shed a bit of light on the application? (I have a suspicion).
Richard Crowley:
Even back in the analog TV era, there was not a special IC for that purpose.
You will have to separate the "C" (color) component from the "VBS" (vdeo, blanking, sync).
Fortunately, that is relatively easy because the "C" component is a fixed-frequency carrier signal.
For NTSC, the FSCis 3.579545MHz, and for PAL, it is 4.43362MHz
So, if you want to boost the saturation, you simply amplify the color subcarrier before you re-insert it into the CVBS.
Your profile does not reveal where you are, but if you are in NTSC-land, you must be careful to avoid diddling the PHASE of the color subcarrier because that will affect the hue of the color. And even a slight change will produce a disturbing shift in color. But PAL is designed to be less sensitive since it reverses the phase of the FSC with every line.
Back in the day we used "processing amplifier" or "ProcAmp" gadgets. They would separately adjust all four parameters:
1) "Brightness" ("pedestal" in the video terms or "offset" in electronic terms.)
2) "Contrast" (luminance gain)
3) "Hue" (color subcarrier phase)
4) "Saturation" (color subcarrier amplitude/gain)
There are still NTSC and PAL proc-amps available on Ebay And maybe even some still available new.
vk6zgo:
To do it properly, you will need a comb filter, as the sidebands of the chroma signal are "frequency interlaced" with the luma signal.
In other words, the sidebands of the subcarrier modulated with the colour difference signals fall in the spectral "gaps" of the luma signal.
You could "cheat" with an ordinary BPF, but there will still be artefacts from the luma signal in the recovered "chroma" from this, which could cause intermodulation.(Remember luma is full bandwidth).
Probably demodulation of the colour difference signal & re modulating it on a chroma carrier is the least problematic way of doing this.
The easiest way would be to look around & see if you can pick up some surplus analog Broadcast equipment designed to do the job.( It was something which was quite commonly done in Broadcasting).
Navigation
[0] Message Index
Go to full version