Video signal processing ( 15 ) :

• Video faders

• Circuit facilitates video fading - Turning potentiometer P1 adjusts the image brightness from normal video to a black image. With the P2 potentiometer ganged to P1 , the sound also varies accordingly. The objectives in building this circuit are to use inexpensive, readily available components and to obtain batteryless operation.   
• Simple Video fader - This is a very basic circuit for fading video signal. You can use this between two video equipments. The circuit is so simple that the impedance matching and some other things are not exactly correct, so might not always work reliably with all equipment. Anyway it is so simple and easy to build that it does not hurt much to try.   
• Video amplifiers make low-cost fader - bandwidths handle SVGA or Super Mac (up to 70-MHz) video signals without degradation, fading is voltage controlled   
• Video fader preserves synchronization - The common video effect "fade to black" is usually accomplished by increasing video signal attenuation to the point where the picture disappears, leaving a black screen. As the composite signal is attenuated, the signal's sync amplitude becomes too small to synchronize the picture properly, and the picture rolls and tears. This circuit shows a simple video "volume control" that operates on the picture but leaves the sync unchanged, allowing a smooth fade to black while maintaining video fidelity.   
   

• Sync related video signal processing

• Digital sync-tip clamping: a new approach to video-signal conditioning - digital sync-tip clamping allows an ac-coupled ADC to digitize analog video without restoring the horizontal timing   
• Video Amplifier with Sync Stripper and PC Restore - This document is an application note of 200 MHz video amplifier, sync stripper and DC restorer in pdf format.   
• Video circuit clamps under all conditions - Many video-circuit clamps operate well in the presence of a composite-video signal but cannot achieve a clamp level with signals other than composite video or in the absence of an input signal. This circuit, developed for the ADC1175 (a popular and inexpensive, high-performance, 8-bit, 20M-sample/sec ADC), provides the normal back-porch clamp function to the input of the ADC in the presence of a composite-video signal. The circuit further ensures that the voltage presented to the ADC is within its correct operating range in the absence of an input signal and forces any signal other than composite video to be within the ADC's input common-mode range.   
• Video Circuit Clamps Under All Conditions - Many video-circuit clamps operate well in the presence of a composite-video signal but cannot achieve a clamp level with signals other than composite video or in the absence of an input signal. This circuit, developed for the ADC1175 (a popular and inexpensive, high-performance, 8-bit, 20M-sample/sec ADC), provides the normal back-porch clamp function to the input of the ADC in the presence of a composite-video signal. The circuit further ensures that the voltage presented to the ADC is within its correct operating range in the absence of an input signal and forces any signal other than composite video to be within the ADC's input common-mode range.   
   

• Video parameter adjustment

• The KD2BD ATV AM Video Modulator - This video signal processing circuit that allows adjustment of video gain, video bias, sync and sync level. The first section of the video modulator performs a video level clamping function. The clamped video is then level shifted. Video is amplified. FM subcarrier audio at 4.5 MHz is also injected. Clamped video is also fed into an LM311 voltage comparator that serves as a video sync detector.   
   

• Reconstruction filters

• Active Filters for Video -Originally, video filters were passive L-C circuits surrounded by amplifiers, but the increased gain-bandwidth product (GBW) of modern op-amps makes it possible to combine them with R-C circuits to achieve smaller, more accurate designs. Active filters developed a bad reputation because of problems getting repeatable results until sensitivity analysis methods provided solutions for these problems in the 1960s.   
• SDTV Reconstruction Filter with Adjustable Group Delay - This application note describes a 5.25MHz, 3-Pole, Butterworth filter using a Sallen-Key realization. It has gain of 2V/V, for driving a 75 back-terminated coax to an overall gain of 1. Such filters are used for video reconstruction of RGB and component video (Y, Pb, Pr) signals following a DAC to remove the higher frequency replicas of the signal, and as an anti-aliasing filter before an ADC.   
   

• Image sharpness processing and enhancement

• Video equalizer sharpens VCR images - sharpens picture images without introducing the shadows, ringing, and noise often observed with commercial video equalizers   
• Video Signal Edge Enhancements - This circuit is based on the claims that the edge enhancement technique would improve the quality of standard TV images. This circuit adds information to the edges of the objects and was reported to bring out more detail. Accordign the designer this circuit gives only a marginal improvement. Still, it is an interesting circuit with which someone might experiment. This circuit is designed for NTSC video in mind.   
   

• Signal inversion

• Video Inverter - This is a simple one transistor circuit to invert the whole video signal, including sync pulses.   

• Time base correction

• Homebuilt digital video TBC/standards converter - This project is a timebase corrector/standards converter with the following features: Two CVBS inputs and one Y/C (SVHS) input; CVBS, Y/C and RGB outputs available simultaneously. This device supports PAL BGHDIN, PAL M, NTSC M, NTSC-Japan, NTSC 4.43 and SECAM input standards. Supports PAL, NTSC and SECAM output standards. Conversion of 60Hz NTSC to 50Hz PAL is possible. The 525->625 line conversion is done using line interpolation. Device supports also freeze, inverted video and mirro image effects. Device has built-in black burst and colorbar features.

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