A pixel test is a test designed to evaluate computer monitor screens and high definition television (HDTV) screens for the presence of pixel defects, such as dead or stuck pixels. Every computer screen or HDTV is comprised of many of these pixels, which can range in number from several thousand to many millions. Pixel tests can come in the form of a program, a prerecorded set of images, a Web site, or can even be the simple act of a person examining a screen closely for defects.
Each pixel is capable of producing a different basic color, such as red, green, blue, cyan, magenta, and others. The pixels as a whole will produce the picture on the screen, and a dead pixel will usually show up as a tiny black dot against a white background. A "stuck" pixel is one that is fixed in one of its color states, so it may not show up as easily against different colored backgrounds. For example, a red stuck pixel that is not able to change colors will not be seen very easily against a red or white background, but may be glaringly obvious when the pixels that surround it are green.
The simplest type of pixel test is to scan the whole picture with the naked eye and search for defects. It will be easier to spot stuck pixels than dead pixels this way because they are tiny, bright colorful spots. Dead pixels are nearly impossible to see with the human eye, and looking for problems on a moving picture is practically impossible unless you know where the defect is. It is becomes more and more difficult as the screen gets bigger; trying to find one dead pixel in a sea of 30 million others is a near impossibility.
There are software programs to test and find dead and stuck pixels, but these still require the human eye to scan the screen to find them. A pixel test program will usually involve a user examining a screen while it changes from one color to another. The colors used will be ideal for spotting a problem pixel. There are also Web sites that offer similar tests, and most of them of cheap or free.
It is important to know what a pixel test is because most manufacturers of HDTVs and computer monitors will typically not consider a few defective pixels to be covered under a warranty. It is up to the consumer to test the device prior to buying it, otherwise defects may turn out to be an annoyance that a person simply has to live with. Sometimes pixel problems can be fixed with additional programs and techniques, but most of the time dead pixels are permanent. This makes buying monitors and HDTVs from unseen sources, such as online stores, without a prior pixel test even more risky.