Page 274 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

FIGURE 10.20
Line 1 Line 2 Line 3 Line 4
Line n Last line
Electron beam
Horizontal retrace
Vertical retrace
10.2 How it works 263
Video screen render/raster of picture.
Blanking: Lines of video are painted horizontally beginning from the top left corner of
the video screen and continuing from left to right further continuing from top to bottom
(Figure 10.20). Once a row has been rendered, the electron beam (for CRT displays) must reposition to the next line for continued rendering. The blanking interval is the time delay whereby the beam is turned off for the interval between the end of one line to the beginning of the next (termed “horizontal retrace/blanking”) or the end of the frame to the beginning of the next frame (termed “vertical retrace/blanking”). Components of the horizontal blanking interval are the front porch (blanking while still moving past the end of one line), the synch pulse (blanking while moving rapid left for repositioning to the next line), and the back porch (blanking while resuming moving right before the beginning of the next line). Color burst happens on the back porch followed by unblanking at the beginning of the line to begin rendering. Blanking is specifically used to avoid rendering of the retrace line across the screen. In television broadcasts, the vertical blanking interval is used to embed and transmit data such as closed captioning, time codes, and copyright information.
Synch: The synchronization signal is embedded within the video signal to synchronize the timing and alignment of the screen paint. The synch signal is comprised of both horizontal and vertical synchronization.
The video picture is built by the sequential updating of a series of individual pixels arranged horizontally and vertically on a picture screen. Beginning on the first line of the picture (in the top left corner of the screen), the electron beam illuminates each pixel from left to right and then from top to bottom. There is a “blanking” line between each paint line whereby the beam is blanked (or