Monitoring the Color Image

by Diana Weynand and Marcus Weise

Unlike television receivers at home, which are set to personal preferences of brightness, contrast, and color, professional monitors must be set to specifications that have been set by the NTSC, PAL, or SECAM standard. Using a professional standard to set up a video monitor is the only way to ensure that the image that is viewed on a monitor is an exact visual representation of the electronic video signal.

The color monitor is in the group of test equipment used to judge the quality of a video image. Adjustments made to a monitor do not affect the video signal itself, but only the monitor used as a reference to view the video image. Other test equipment is used to view different aspects of the video signal. These will be covered in the following headings.

The Human Eye

The human eye is not an absolute measuring device, but an averaging device. Eyes, like noses, get desensitized when exposed for too long to the same stimulus. As a result of looking at one or more colors for a long period of time, mistakes in color balance can easily be made. During set up, it can be helpful to look away periodically for a few seconds so the eyes don’t become desensitized. In the case of a long set up procedure, it might be best to walk away for a few minutes into a different room with different light. It is imperative to always apply set up procedures to the monitor in the room light that will be used when viewing the video image.

Color Bars

The test signal that is used to set up a video monitor is color bars. Color bars is the international professional reference used to ensure that the color of the images that follow look the same on any monitor as they did when they were created. The color bar signal contains everything needed to set up a color monitor. The signal contains color chips representing each primary and secondary color, analog or digital black, white, and reference chips for gray. (Figure 7-1)

There are several varieties of color bar displays approved by the International Organization for Standardization, or IOS, the organization that sets international standards. Each of these displays contains variations of testing parameters. Different color bars have different elements. For example, some color bar displays do not have a black reference chip. Some color bar displays have multiple black reference chips. Some displays have more than one white reference chip. All color bar signals have the basic chrominance and luminance references.

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Excerpted from "How Video Works" by Diana Weynand and Marcus Weise (Published by Focal Press). An easy to understand explanation of the entire world of video. A complete guide from analog video to all the new digital technologies, including HD, compression and encoding. Purchase Now

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