Tips for using video test patterns and signal generators more effectively.
Using an SMPTE bar pattern to analyze video performance, Tom Schulte, CET, an application engineer at Sencore in Sioux Falls, SD, uses calibration instrumentation to help make
Tips for using video test patterns and signal generators more effectively.
Using an SMPTE bar pattern to analyze video performance, Tom Schulte, CET, an application engineer at Sencore in Sioux Falls, SD, uses calibration instrumentation to help make color adjustments to the display.
Credit: Gary Latza/PeopleScapes
Video test patterns are designed to be applied to the input of a video processing system to be evaluated visually, electronically measured on a video display, or analyzed with an electronic test instrument (e.g. waveform monitor) at a later point in the system. They may also be directly applied to the input of a video display to test or calibrate the display itself. In that case, the test pattern images will be evaluated visually or measured electronically with a light measurement device.
The required visual evaluations typically aren't very subjective because most people with somewhat normal eyesight and an understanding of what they're looking for from each test pattern will give substantially the same evaluation or adjustment. Each different video display or system performance characteristic is typically verified or adjusted with a test pattern designed specifically for that performance characteristic. Anyone with normal eyesight and a basic understanding of the desired image characteristics will normally be able to make any indicated adjustments or evaluate the display's performance as well as almost anyone else.Choosing the right VSG
Video test patterns are usually produced by a video signal generator (VSG). This generator must be capable of producing the required signal format(s) to match the intended video systems or displays. These formats may include NTSC, PAL, ATSC (480p, 1080i, etc.), computer monitor formats (640x480, 1024x768, etc.), or other specialized system signal formats. The generator also needs to be capable of supplying these signals through the proper type of signal connection(s) to interconnect with the intended video systems or displays. These signal connection types may include analog modulated RF signals and baseband composite, S-video, component (YPbPr), or RGB video signals. Desired digital signal connection types may also include digital modulated RF signals (ATSC RF), and baseband DVI, HDMI, SDI, or HD-SDI video signals.
A video generator needs to produce output video and sync signals with a certain degree of accuracy — to ensure observed or measured characteristics of the test patterns can be evaluated effectively without being adversely affected by poor generator accuracy. The generator's pixel clock also needs to reach a high enough frequency to produce full, normal image resolution at the desired signal formats.DVD reference disks
Test patterns are also available on DVD reference disks (or from THX Optimizer, which is available on a number of movie DVDs). These reference disks are extremely useful in evaluating DVD player performance and for optimizing the various video adjustments that are provided in different models of DVD players. Normally, the associated video display would first be fully adj