PLUGE BARS
There is another color bar display that is helpful in setting up a color monitor. These bars are referred to as PLUGE bars, which stands for Picture Line Up Generating Equipment. PLUGE bars contain the standard color bar pattern, plus two additional references. The first reference is a set of three color chips and one white chip separated by three black chips going across the lower third of the screen. (Figure 7-3) The second reference is two additional black chips within the larger black chip in the lower right hand corner of the screen.
The four chips that appear across the lower third of the screen are used for setting the hue and saturation of the monitor. The four chips — blue, magenta, cyan, and white — each separated by black, are in the opposite order from the color bars. All four chips contain the color blue. With the red and green displays turned off, there is a blue chip under each of the blue bars. Without PLUGE bars, it was necessary to scan the entire monitor and try to balance the four color bars against each other across the screen. With the use of the PLUGE bar signal, the eye does not have to cover such a wide area when comparing signals.
Use the hue and saturation controls as above to make all the blue bars, and the chips underneath them, the same. The additional black chips in the black field aid in setting brightness. One chip is 4 units of video, or blacker than analog black. The other is 10 units, or dark grey. These are in addition to the 7.5 units of analog black.
The proper brightness for the monitor can be set by adjusting the brightness control until the 10 unit chip is just barely visible. If the brightness is set too high, the 4 unit chip becomes visible. If the brightness is set lower than the point at which the 10 unit chip is just visible, the colors will appear dull and the picture dark.
Color Image
If everything was adjusted correctly, the white chip in the color bar image will appear pure white without a hue and the black will appear pure black with no color shading. Once a good monochrome image has been set, the next step is to restore color to the monitor. Whatever procedure was used to turn color off should now be reversed to turn color back on. Color bars continue to be used as the video input signal and color reference.
Some monitors have a switch marked Set Up. This switch collapses the vertical drive so that the picture is reduced to a line or bar across the tube. This acts as an aid in setting up the basic balance of the three colors. However, the reduced scan may have a different color balance than the full picture, and therefore may not be totally reliable.
Once the monitor is set up correctly, the details of the electronic video signal can be viewed on scopes. |
