With Display Daily you can count on receiving the most up to date information on all segments of the display technology world. The expert team of writers and analysts are truly dedicated to the dissemination of leading edge and sometimes bleeding edge information on display technologies for you to revel in each day. One topic that has not been addressed in depth is display calibration. Why it is necessary to consider display calibration, and what does it actually entail? As the director of the newly launched Imaging Science Foundation (ISF) Commercial Program which teaches the science and art of display calibration, please permit me to take the proverbial "whack" at explaining why it is important.

Alan Brawn
Insight Media Consultant

It is a fact of life that video display devices never perform at their peak levels as they are delivered from a manufacturer. Manufacturers provide a generic setting of the display parameters. For consumer displays, these settings are often intended to make the TV stand out in a big-box store, not optimize the image quality in the living room. Most often they set the brightness and contrast at exorbitantly high levels and the "evil" sharpness control at the ¾ position. For proof of this go to any big box store and look at all the displays and sit in wonder at the patchwork quilt of images that you encounter. On the commercial side, go to nearly any network operation center with a big video wall and see the differences from screen to screen. The digital age is upon us with HDTV, high resolution graphics, and ever increasing screen sizes. This would lead to overall improvements in color, contrast, and picture performance for the end user if the display is set up correctly. Hence the need for display calibration versus mere adjustments.

The issue of calibration goes beyond randomly turning some knobs or adjusting some settings on a display. Each display type has it own unique "personality" and responds to inputs and environments in different ways. Understanding the nuances of each technology and how to address each type of input to provide the "perfect picture" is a must. The bottom line is that one size does not fit all. Don Stewart, of Stewart Filmscreen fame, preaches the gospel of dynamic range in a picture. Do not bother looking for this as specification because it is not a single issue rather the blending together of art and science in a picture to maximize the impact of images on screen in a particular set of "living" conditions. This blending or tweaking of settings cannot be done in a vacuum but must be done in the environment in which the display and images will "live." According to Don, and most display experts agree, there are as many types of display calibrations as there are applications and environments. The film industry has done its best to standardize on the projector, the film or more recently the digital signal, relative to the typical theater environment in order to set a uniform standard. The other parts of display world are fraught with inconsistencies and nuances that must be accounted for in display calibration.

Sans a scientific process that is repeatable, we are left with a rough order of magnitude estimation of what "looks" right. In a recent calibration session we performed the "eyeball estimation" as a point of reference. We then went back with our video test generator, colorimeter and light meter to see just how accurate we were. Much to our dismay but not surprise, we were way off. The color temperature was at 2x the D65 we were aiming at. The white level and black levels were both off substantially and the gamma was not tracking as it should have been. We then applied the scientific calibration procedures and wanted to see the difference in the image. The properly calibrated image looked more natural in terms of color space, detail in the blacks was restored, and brightness did not over power the image on screen. In short, we took the display technology and maximized the image quality for the inputs and environment. This still begs the question: What does display calibration entail?

Fundamentally, calibration is the process of optimizing the projector or flat panel display to reproduce the information from video and data sources (DVD, HD, Satellite, PC, etc) in a manner that closely approximates the quality and dynamic range experienced in a 35MM film theater. Seeking the "holy grail" of film performance and dynamic range, calibration involves color, contrast, and detail along with the environment. A good, well calibrated electronic display can match film in most properties but avoid the image jitter and other artifacts of the film experience. The main elements of calibration are:

1. Maximizing Contrast Ratio: The difference between the darkest and lightest image details the display can reproduce.
2. Optimizing Gray Scale: Adjusting gray scale means the display properly reproduces the color of white at D65 (6500° Kelvin) which is done by adjusting the ratio between the Red, Green, and Blue (RGB) pixel levels. All colors reference this "white point" so it is critical that it be set accurately.
3. Optimizing the Gamma Curves: This defines how much light the RGB pixels emit for a given brightness level prescribed by the video signal. This setting is especially important to get details in the shadows.
4. Optimizing Color Space and Reproduction: This is directly linked to the gray scale optimization.
5. Flat Field Uniformity: The projector displays a pure white image from a white test pattern, free of any blotches or colors that alter the image.

Each display manufacturer will have different levels of calibration capability in their products for the end user to use. At one end of the spectrum are studio monitors used for grading and color correcting video signals. These monitors have calibration hardware and software built in and are typically calibrated daily. For good reason, many manufacturers of consumer electronics limit the access to internal calibration capabilities to the basics of brightness, contrast, color temperature (as presets), and tint/hue adjustments for color. They recognize that a good deal of harm can come from an inexperienced consumer randomly making adjustments to their displays and getting lost in the process. The amount of customer service follow up required to return the display to even the factory default image quality is not acceptable. Thus, the need for certified technicians to perform calibrations on behalf of those not qualified to perform the tasks themselves.

Many physical factors are important in display calibration including but not limited to visual acuity, ambient light, reflected light, and off axis viewing. Calibration is simply the last task that must be undertaken to ensure that the display system is optimized for the intended purpose in the environment which it resides. Once again, one size does not fit all.