COMPOSITE VIDEO
1.2 Measure voltage and standard composite video.
1.3 Determining the parameters of composite video.
EQUIPMENT USED:
1 VCD / VTR
1 Oscilloscope 40 MHz and passive probe
An RCA cable connector - BNC (75W)
EQUIPMENT USED:
1 VCD / VTR
1 Oscilloscope 40 MHz and passive probe
An RCA cable connector - BNC (75W)
Circuit diagram:
INTRODUCTION:
The most fundamental job of a video decoder is to separate the color from the black and white information for video composite signals. This task has been achieved many ways since the introduction of color television over 50 years ago. Many different separation methods have been used through the years. With the availability of new cost effective technologies, the consumer has been seeing a gradual improvement in picture quality and detail. Advances in display tube technology and semiconductor processes have pushed the technological envelope providing sharper, more robust video. But separating the chrominance from the luminance information is especially challenging due to the fact that the signals overlap each other in the frequency spectrum. How do you separate them, while minimizing display artifacts?
Composite Signal Construction
The composite video signal is constructed with 3 basic elements:
- Luminance Information from DC to 5.5MHz (B&W Detail)
- Chrominance Information modulated onto a carrier (at 3.58MHz or 4.43MHz)
- Synchronization Information (Horizontal and Vertical Sync)
The three analog elements of a composite video signal carry all the information necessary to display a two dimensional picture on a cathode ray tube (CRT) television.
Luminance (a B&W World)
The luminance signal carries the black and white parts of the picture. This component of the composite video signal requires the most bandwidth (typically to 5MHz), and signal integrity, to convey sharp and clear images. Edge information, brightness, and contrast of the image are entirely contained in the luminance portion of the signal. Until 1947 the broadcast video signal was only black and white. To maintain compatibility with the installed equipment of the time, color or chrominance information was added to the luminance signal
Chrominance (an Add-On)The chrominance information is quadrature modulated onto the luminance information. The chrominance is interleaved into the video signal bandwidth between luminance spectra. The chrominance modulation scheme utilizes an I, Q (U, V for PAL) coordinate system where hue and saturation is in vector format. A camera sensor captures light in Red, Green, and Blue (RGB) format. The RGB signal is converted into Y (luminance signal) and I, Q (Color Difference signal) format along with the synchronization information. The I, Q (commonly referred to as C) color information occupies a smaller bandwidth than the Y signal. C bandwidths typically range from 0.6MHz to 1.3MHz. The chrominance signal is modulated onto a carrier. The carrier resides at 3.58MHz for NTSC signals and 4.43MHz for PAL signals. The chroma information must be separated out of the video signal to demodulate it to baseband. This is difficult because luminance information that resides from 2MHz to 5MHz cannot be differentiated from chroma information. Several techniques have been tried over the years to improve separating Y and C, each increasing in complexity and performance.
Don’t Forget the SyncThe synchronization information is also imbedded in the composite video signal and occupies precious amplitude range of the video signal. Horizontal Sync, Vertical Sync (also know as Vertical retrace) and the Color Reference Bursts are embedded in the composite waveform. Figure 2 shows a typical composite signal.
Composite Video Signal Construction
Composite video signal containing variations of the camera signal (image information), blanking pulses (blanking), and synchronization pulses (sync).
Figure 1. Three sets of composite video signal is a variation of the camera signal, blanking pulses, and synchronizing pulses. (A) camera signals (image information) to a single horizontal line, (b) H blanking pulse signal is added to the camera, (c) Toll-alignment of H added to the pulse discharge.
Figure 2 composite video signals for two horizontal lines
In figure 2, the amplitude of voltage and current are shown sequentially for MRV two horizontal lines in the shadows, as time increases Dalan horizontal direction, the amplitude is changed to white shade, gray, or black in the picture. Starting from the far left at time zero, the signal at the level of white and MRV file located on the left image (the image).
Once the first line dipayar from left to right, found different cameras with different amplitude signal corresponding to image information is required. After penjejakkan (trace) horizontal camera produces the desired signal for one line, MRV file located on the right image (image or image). Then the discharge pulse is inserted in order to restore the video signal amplitude to the top to the black level, so that repetition of traces can be left empty.
After emptying time long enough to cover the trail repetition, emptying the voltage is removed. Then & MRV file located on the left, ready to memayar next line. In this way each horizontal line dipayar respectively. Note that the second line shows the dark image information near the black level.
With regard to time, the amplitude of the signal-amplitude right after emptying in Figure 2 shows the information in accordance with the left side at the start line of MRV. Just before discharge, the signal variation corresponds to the right side. Appropriate information in the middle line of MRV is half the time between discharge pulses.
Figure 3. Details of horizontal blanking and synchronizing pulses.
Details of the horizontal blanking period as figure 3. Intervals marked H is the time required to memayar a complete line including tracking and loop trail.
Pulse-Pulse Alignment in Time Decommissioning V
Sync pulses are inserted in the composite video signal during vertical blanking pulse width shown in Figure 4. This includes pulses to equalize, pulses vertical alignment and horizontal alignment of multiple pulses. Signal-signal is shown at intervals of time at the end of the field and the next one, to describe what happens during the vertical blanking time. Both signals are shown one above the other are the same, except for half-line shift between successive fields are required for MRV intertwined odd lines.
Starting from the left in Figure 4, the fourth-last line of MRV horizontal raster shown on the basis of joint discharge pulses and horizontal alignment is needed. Immediately after following the last visible line, the video signal is made into the black by the vertical blanking pulse in preparation for the repetition of vertical trace. Vertical blanking period begins with a group of six pulses MRV, which separate the half-line intervals. Next is the vertical alignment pulse produces real jagged vertical flyback in a series of MRV. Serration also occur at intervals of half a line. Thus, a complete vertical alignment pulse width is three lines. Following the vertical alignment is a another group of six pulse equation and a series of horizontal pulses.During the vertical blanking period as a whole, there is no information on the resulting image, because the signal level is black or blacker than black so that the repetition of vertical traces can be left empty.
In a signal at the summit, the first pulse is a full line of credit beyond the previous horizontal alignment; in signals below for the next field, the first pulse is as far as half a line. The difference this time and a half lines between the even fields and odd continues through all subsequent pulses, so that the pulses of the vertical alignment for successive fields MRV interwoven set time for the odd lines.
Decommissioning & MRV V and V (V Blanking and V Scanning)
Serrated vertical sync pulses that force the vertical deflection circuit to start the flyback. However, the flyback generally will not begin with the start of vertical alignment because the alignment must build a toll-charge in a capacitor in order to trigger circuits & MRV. If we assume that the vertical flyback starts with the leading edge of the third serration, the elapsed time from one line for vertical alignment before the flyback starts. Also six pulses to equalize the same with the three lines before the vertical alignment. So 3 1 = 4 lines left blank at the bottom of the image, right before the vertical loop trail begins.
How much time is required for the flyback circuit depends on MRV, but the repetition time of a typical vertical traces are 5 lines. Once the loop trail MRV file from the bottom to the top of raster, produced five complete horizontal lines. Repetition vertical trail can be completed with ease during vertical blanking time. With 4 lines left blank at the base before the flyback and 5 lines emptied during flyback, 12 lines remaining from a total of 21 during during vertical blanking. The 12 blank lines at the top raster in the vertical direction of the surface tracking down. In summary, 4 lines left blank at the bottom and 12 on the top line in each field. In the framework of a total of two fields, 8 lines emptied at the base and 24 lines at the top. MRV lines generated during vertical tracking, but that made black by the vertical blanking, forming black rods at the top and the bottom of the image.
High image is slightly reduced by the discharge, compared with a raster that is not emptied. However, height can be fixed easily by enlarging the amplitude of the sawtooth waveform for vertical & MRV.
High image is slightly reduced by the discharge, compared with a raster that is not emptied. However, height can be fixed easily by enlarging the amplitude of the sawtooth waveform for vertical & MRV.
EXPERIMENT PROCEDURE:
1. Set-up equipment as shown above, connect the video out VCR / VCD with CRO input.
2. ON the instrument.
3. Set the appropriate CRO to be easily observed (use MODE switch on the TV-H position and / or TV-V, in accordance with the observed images.) When seeing a wave of horizontal synchronization MODE switch put on the TV-H position, while to see a wave of vertical sync put the MODE switch on the TV-V position.
4. Observe and picture synchronization pulses and horizontal blanking, vertical blanking pulse, the front porch and rear, and image information.
5. Image of the wave forms and determine the voltage. QUESTION:
1. What is the frequency of horizontal sync and vertical sync?
2. What system is used in the video?
EXPERIMENT RESULTS :
1. What is the frequency of horizontal sync and vertical sync?
2. What system is used in the video?
EXPERIMENT RESULTS :
1. Without Cassette CD
TV IMAGES V :
TV IMAGES V :
1.
2.
note : T/D = 2 ms & V/D = 0,2 V
2.
note : T/D = 2 ms & V/D = 0,2 V
2 . Cassette CD has not been in play
1.
2.
Note : T/D = 2ms & V/D = 0,2V
3. With cassette CD after the play
TV IMAGES V :
1.
2.
Note : T/D = 1 ms & V/D = 0,2 V
ANSWER QUESTIONS:
1. What is the frequency of horizontal sync and vertical sync?
Frequency = 31.68 KHz horizontal synchronization
Frequency = 70.71 Hz vertical synchronization
2. What system is used in the video?
The system used is to use the system pemodulasian AM because it can be seen from the changes in amplitude and has a spectrum of AM.
1. What is the frequency of horizontal sync and vertical sync?
Frequency = 31.68 KHz horizontal synchronization
Frequency = 70.71 Hz vertical synchronization
2. What system is used in the video?
The system used is to use the system pemodulasian AM because it can be seen from the changes in amplitude and has a spectrum of AM.
CONCLUSION:
- Comprises a composite video signal consisting of variations of image information, pulse blanking (blanking), and pulse alignment (synchronization), each based on a function of time.
- Interval marked H is the time required to memayar a complete line including tracking and loop trail.
front porch pulse = 0.02 H
horizontal sync pulse H = 0.08
back porch pulse = 0.06 H
horizontal blanking pulse = 0.16 H
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