WHY CALIBRATE?

There are 3 ways to “calibrate” a TV

1) You take the TV out of the box, put batteries in remote; adjust the TV controls (Brightness, Contrast, Color, Tint, and Sharpness) by eye. This is about the same as telling time without a reference (sundial, clock, GPS, etc.)

2) You can adjust the TV controls with Industry Standard test patterns found on AVIA, Digital Video Essentials, and Sound and Vision DVD’s. You now have a reference, but are limited by adjustments available from remote control.

3) ISF Calibration by a trained technician. He uses the television service menus to adjust TV controls, the industry standard DVD’s to adjust regular TV images to maximum resolution of 480P. He also uses a High-Definition test pattern generator to adjust the maximum resolution to limit of the TV. With these calibration procedures, the quality of the TV picture is only limited by the TV and technicians experience. Almost everyone has an opinion of what is a perfect picture, despite lacking a reliable reference for the original image. Ultimately the only perfect picture is an accurate picture, and the only way to achieve accuracy is through professional calibration.

ISF - Image Science Foundation, did research to find a repeatable way to make TV pictures accurate. It’s all based on standard’s developed in the 1950’s, and then defined in the 70’s.

Let's start with a little background. Mathematicians and engineers set our NTSC (National Television Standards Committee) system on paper in 1953. Their ideal system was not easily implemented. In fact, there are still some parameters that we have difficulty implementing today. They have been set up as goals for the coming of HDTV. In the meantime, we've been improvising around some of the original ideas that were difficult to implement. The lack of a single, workable standard for setting color picture monitors that includes monitor design more than any other factor, has contributed to NTSC being known as "Never Twice the Same Color." In the original concept of the NTSC system, the monitor was supposed to be a fixed device, with all variability controlled at the picture source. Several things went wrong with that concept. First, usable green phosphors couldn't produce the ideal primary green point of the NTSC system. The right color of green had a long decay time relative to the red and blue. It was the same green used in oscilloscopes. Also imagine that phosphors are like LED’s. When you buy a green LED, there is no standard for how ‘green’ it will be. Manufacturers produced picture tubes with whatever red, green, and blue phosphors they could make or buy. Since the original NTSC primary colors weren’t being met, monitor calibration became ‘best guess’. Set up by eye, was the rule of the day. Also, early monitors weren't as stable as today's, so they needed to be adjusted often The situation had deteriorated in the movie and TV show world to a point where SMPTE (Society of Motion Picture and Television Engineers) had to establish a workable standard around existing technology. Their 1970 efforts at establishing standards provided difficult to implement. As an example, one of the most important parameters, gray scale tracking was accomplished solely with an optical comparator, a time consuming art at best. Technological developments in both monitors and test equipment for calibrating monitors in the early 1980s made it possible for SMPTE to develop more easily implemented practices. Companies like Graseby, Minolta, Philips, Photo Research, Sencore, Tektronix, and Tomas are now providing test instrumentation necessary to make setup of monitors easier. SMPTE's effort to bring these developments together will help improve the quality of NTSC video. Their current goal is to bring the NTSC viewing environment closer to the consistent conditions originally envisioned by the NTSC.

One of the originators of ISF was Joe Kane. He was on the SMPTE committee which originally created the standards. Joe then created a reference with the laser disc “A Video Standard” and later another one “Video Essentials”. These laser discs were the first consumer accessible reference test patterns available. The consumers that wanted the very best picture were able to use these discs to find the limitations in their TV’s. Some even went so far as to find commercial test equipment to measure TV color with these discs.

Manufacturers do check the calibration on each set, as part of the quality control process. But, this is just to make sure each TV is functioning. If a manufacturer does perform any calibration, it is limited to what can be adjusted on the assembly line in just a few seconds. Marketing has determined the default color settings, so it will look OK under the ‘warehouse lighting’ of mass retailers. The goal is to sell TV’s, and if every TV looks different, then it is easier to explain why one is better than the other, without getting into features and ease of use. When calibrated, all TV’s should look the same. Only the brightness would differ based on the type of device.

However, manufacturers choose color of phosphors based on marketing’s decisions of what “color” is easiest to sell. An ‘oranger’ red will make skin look tanned. A ‘deeper’ blue will make sky scenes look more vivid.

It takes a small amount of difference to be noticeable on a test pattern.

But with a color picture, the small amount of difference is more subjective.

Brightness and Contrast do affect the overall picture also.

You should be able to see 10 distinct levels of white with this test pattern. If on the right side (white) you can’t see a difference in 80, 90 and 100 blocks of white, you will damage your TV over long periods of time. A plasma TV will be damaged in less that 6 months. This damage is known as ‘burn-in’ and is permanent. The damage is the same as you see on the older ATM machines, where you can still read the words on the screen even though the screen has changed.

By simply adjusting the brightness and contrast with a reference DVD and this test pattern, you can prolong the life (and quality of picture) of your TV.
The other end of the video scale is black. If you can’t see a difference in the 30, 20, and 10 blocks of black, then your picture will not have any details in shadows and dark scenes. This is another step in making sure that your picture is adjusted to that ‘reference’ that we wrote about earlier. However, black is a moving target. The regular TV standard of black is not really black. To be able to transmit images with less effort, the NTSC (National Television Standards Committee) decided that 7 ½ % above true black, or 0, was good enough. So TV shows are recorded with black as 7 ½ instead of 0. Even DVD’s are done this way, and only a few DVD players will actual reproduce real black (0%). Only HDTV uses 0% black as black. There are test patterns to show this difference and adjusting the contrast with these patterns will allow you to get the most out of your TV.

So, now we have talked about how Grey Scale, Brightness, and Black Level affect the picture. We haven’t talked about Color and Tint yet. That will be the next article.

9/1/2003

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