Cross Pulse Display
On a professional video monitor, the image can be shifted horizontally to make the horizontal blanking period visible. The image can also be shifted vertically to make the vertical blanking interval visible. When the image is shifted both horizontally and vertically at the same time, the display is known as a cross pulse or pulse cross display. A cross pulse display is a visual image of what is represented electronically on a waveform monitor. This display shows several of the signals created in the sync generator.
Other Signal Outputs
There are several other outputs from the synchronizing generator that are used for testing or other purposes. These test signal outputs are not so much used for driving the system as they are for checking it, or checking the synchronizing generator itself.
Quite often, test signal outputs and black burst or color subcarrier appear at the front of the sync generator for ease of access, though they are also available at the back of the sync generator. Horizontal and vertical drive pulses may be available at the rear of the sync generator, as they are not used for testing purposes or to drive any other piece of equipment other than a tube camera. Test signals that are available from a sync generator are discussed in Chapter 21.
Vertical Interval Signals
The NTSC analog video image is 525 lines, 480 of which represent picture information, referred to as active video. The remaining lines in the vertical interval are used for synchronizing information. Test signals are inserted in the vertical interval as well. While not part of the active video, they are a valuable part of the composite signal.
These signals are usually created by devices connected to one or more of the outputs of a sync generator. These extra signals can then be inserted in the vertical interval. These signals may include vertical interval test signals, vertical interval reference signals, closed captioning, teletext, commercial insertion data, and satellite data.
In the case of the vertical interval test signals (VITS), a test signal generator can create one-line representations of several test signals.
These one-line test signals are inserted in one of the unused video lines in the vertical interval. The VITS can be displayed on an oscilloscope.
This test signal provides a constant reference with respect to the active video contained within the frame.
The vertical interval reference signal (VIRS) was developed to maintain color fidelity. Small differences in color synchronization can occur when signals are switched between pieces of equipment. The VIRS provides a constant color reference for the monitor or receiver.
Without the VIRS, the color balance of the image may change.
Closed captioning was originally developed so the hearing impaired could watch a program and understand the dialogue. In closed captioning, a special receiver takes the information from the verticalinterval and decodes it into subtitles in the active video. Closed captioning may also be used in environments where the audio may not be appropriate or desired. Technically, since closed captioning appears on line 21, which is active video, the data is not truly in
the vertical interval.
Teletext can be used for broadcasting completely separate information unrelated to program content. An example of this is seen on many cable news stations. While the camera may be covering a news story or pointing to an anchor, the ticker tape of information below the image is an ongoing feed of text.
Commercial insertion data can be used to automatically initiate the playback of a commercial. This can eliminate the possibility of operator error. The data are designed to trigger the playback of the required material at the appropriate time, as well as for verification that the commercial was broadcast as ordered.
Satellite data contains information about the satellite being used, the specific channel or transponder on the satellite, and the frequencies used for the audio signals.
The blanking portions of the video signal, both horizontal and vertical, carry critical information. In addition to synchronizing, the blanking periods are used to carry other data that enhance the quality and usefulness of the video signal.
On a professional video monitor, the image can be shifted horizontally to make the horizontal blanking period visible. The image can also be shifted vertically to make the vertical blanking interval visible. When the image is shifted both horizontally and vertically at the same time, the display is known as a cross pulse or pulse cross display. A cross pulse display is a visual image of what is represented electronically on a waveform monitor. This display shows several of the signals created in the sync generator.
Other Signal Outputs
There are several other outputs from the synchronizing generator that are used for testing or other purposes. These test signal outputs are not so much used for driving the system as they are for checking it, or checking the synchronizing generator itself.
Quite often, test signal outputs and black burst or color subcarrier appear at the front of the sync generator for ease of access, though they are also available at the back of the sync generator. Horizontal and vertical drive pulses may be available at the rear of the sync generator, as they are not used for testing purposes or to drive any other piece of equipment other than a tube camera. Test signals that are available from a sync generator are discussed in Chapter 21.
Vertical Interval SignalsThe NTSC analog video image is 525 lines, 480 of which represent picture information, referred to as active video. The remaining lines in the vertical interval are used for synchronizing information. Test signals are inserted in the vertical interval as well. While not part of the active video, they are a valuable part of the composite signal.
These signals are usually created by devices connected to one or more of the outputs of a sync generator. These extra signals can then be inserted in the vertical interval. These signals may include vertical interval test signals, vertical interval reference signals, closed captioning, teletext, commercial insertion data, and satellite data.
In the case of the vertical interval test signals (VITS), a test signal generator can create one-line representations of several test signals.
These one-line test signals are inserted in one of the unused video lines in the vertical interval. The VITS can be displayed on an oscilloscope.
This test signal provides a constant reference with respect to the active video contained within the frame.
The vertical interval reference signal (VIRS) was developed to maintain color fidelity. Small differences in color synchronization can occur when signals are switched between pieces of equipment. The VIRS provides a constant color reference for the monitor or receiver.
Without the VIRS, the color balance of the image may change.
Closed captioning was originally developed so the hearing impaired could watch a program and understand the dialogue. In closed captioning, a special receiver takes the information from the verticalinterval and decodes it into subtitles in the active video. Closed captioning may also be used in environments where the audio may not be appropriate or desired. Technically, since closed captioning appears on line 21, which is active video, the data is not truly in
the vertical interval.
Teletext can be used for broadcasting completely separate information unrelated to program content. An example of this is seen on many cable news stations. While the camera may be covering a news story or pointing to an anchor, the ticker tape of information below the image is an ongoing feed of text.
Commercial insertion data can be used to automatically initiate the playback of a commercial. This can eliminate the possibility of operator error. The data are designed to trigger the playback of the required material at the appropriate time, as well as for verification that the commercial was broadcast as ordered.
Satellite data contains information about the satellite being used, the specific channel or transponder on the satellite, and the frequencies used for the audio signals.
The blanking portions of the video signal, both horizontal and vertical, carry critical information. In addition to synchronizing, the blanking periods are used to carry other data that enhance the quality and usefulness of the video signal.
3 comments:
Thank you! Very useful, I'm having an exam tomorrow and i was searching some info about "Pulse Cross", now i got it!
Greetings from Spain!
You will also find Macrovision copy protection in the V an H intervals.
In the digital realm, 480 lines would be 23-262 and 285-524 in Fields 1 and 2, respectively. In broadcast standards, it would be 486 lines - 21-263 and 283-525. However, some screencaps done in the full 486 line window on a website dealing with restorations of 2" quad videotapes show only 484 lines used, given what has been said about 483 lines being used (484 if digitized). In such realm, F1 and F2 would be 22-263 and 284-525. To mention the horizontal resolution as per 13.5 MHz sampling clock, of all the other pulses - sync, EQ, and vertical serrations - would take up too much space.
Post a Comment