Calibration – What Is Wrong with This Picture?
What’s wrong with this picture? Here is a beautiful outdoor family scene, in a quality that you might see when viewed on one of today’s high-end HDTV video displays. Does the display accurately reproduce what your eyes would see if you were standing just up the hill from this family’s camping site? Does the display provide an honest sense of being there? It can, but only after being professionally calibrated. Here’s why.				Glen Kropuenske SENCORE, Inc. Application Engineer 1.800.736.2673 or 1.605.339.0100 mailto:ae@sencore.com http://www.sencore.com
Actually, there are a number of controls misadjusted on this video display. For example, the black level is set too high, making the rich black areas of the picture muddy gray.
What’s Wrong? Movie cinematographers go to painstaking levels to be sure what is captured on film and transferred to electronic video is an exact reproduction of the scene’s light and color content. Color balance (temperature) of pickup cameras, color saturation levels, and light levels are all closely monitored. How else could you get the sense of being there when you watch that movie at your local movie theater?
When program material is cut to a DVD or broadcast, the process is both electronically monitored and visually monitored by engineers using displays that are calibrated to industry standards. Film to electronic video transfers and display calibration procedures are all conducted according to industry standards established by the Society of Motion Picture and Television Engineers (SMPTE). Similar Broadcast standards, such as NTSC and ATSC, insure proper broadcast video. These standards have been perfected over the last 60 years and are meticulously adhered to.
If the video content on the signal coming into the display contains painstakingly accurate scene information, then the last step is simply reproducing it on the display screen. Houston, we have a problem! If you have walked into a TV showroom, you likely noticed that each display has a slightly different looking picture. In theory, if each was calibrated like a broadcast studio monitor using SMPTE procedures, they would look nearly identical. More importantly, each display would be accurately reproducing the video scenes. Goal accomplished, right? Not so fast. Video display manufacturers have discovered that displays sell better when the brightness is turned up, picture transitions emphasized and, grey scale is shifted blue. Furthermore, they have introduced non-standard picture corrections or enhancements such as scan velocity modulation (SVM), sharpness control, and color enhancement or “red push.” These features combined with automatic color adjustment and room light sensing correction further degrades the true picture reproduction. It should then be no surprise why the grass is bluish, jersey colors are not the right color, faces are red, color is washed out and/or picture distortion trails off picture transitions.
Even if the manufacturer calibrated to known standards, it would NOT guarantee accurate reproduction.	Is it up to the manufacturer to get it right? Even if the manufacturer calibrated to the known standards, which would increase the price, it would not guarantee accurate reproduction. Electronic display components such as CRTs, Plasma panels, DLP bulbs age at varying rates. This causes light level, color, color balance and, video peaking variations upon installation, during burn-in and through the life of the display. Unique room lighting conditions or changes can also cause variation.
Professional Calibration What can be done? Consumer Electronic Manufacturers continue to improve display technologies. The good news is that most displays come equipped with a full set of control and adjustment capabilities. This means you can calibrate that big screen picture so it reproduces video comparable to that broadcast studio monitor calibrated to SMPTE standards. Yes, with the proper procedures, equipment and know how, you can transform the picture into the same beautiful life-like pictures and scenes that the artists intended. Furthermore, a precision calibration can make a modest display look like a system that costs thousands of dollars more. Most installation technicians make adjustments until it looks right in their eyes. This is NOT professional calibration, as they do not adhere to any specifications or standard procedures. While some improvement may be made, a standard performance level is not realized and there is no consistency between installations and technicians to insure good quality display performance. Do you have to work in video production or at a broadcast station to learn how to do a professional calibration? Absolutely not, it’s not rocket science! You simply need to learn a few basic procedures and apply the appropriate tests and adjustments. Here are the nuts and bolts of it.
Display Calibration – Nuts & Bolts To calibrate a video display, you will perform some or all of the following steps. You will accurately adjust the black level (brightness control), peak white level (contrast control), color saturation and hue. You will disable the sharpness enhancement circuit (no more shadow artifacts surrounding all the faces and text), the SVM circuit (fine detail won't be all blurred together), the auto-color circuit and the room light sensor (auto-brightness, iris, etc.). You will adjust the background grayscale color (white balance) to the industry standard white reference (D65) for which the overlaying colors are designed. If possible, you will adjust for accurate color decoder operation, with no red push (allows rich, normal saturation for all other colors). Plus, you will adjust the focus and geometry controls for optimum picture quality. While calibration may sound complicated at first, once you have calibrated a few displays, it will seem like clockwork. It does help to have test equipment designed specifically to make every step of the calibration as easy as possible. The typical calibration steps are as follows: 1) Disable the room light sensor feature, preset the black level and preset the peak white level. This puts the video display into a normal operating range, so that all other controls can be adjusted properly. 2) Adjust the focus and geometry (picture size, centering, shape, CRT convergence), if necessary. Disable the sharpness correction, scan velocity modulation and auto-color. 3) Adjust the grayscale tracking; also called white balance. 4) Adjust the brightness, contrast, color, hue and sharpness presets for optimum picture quality. The control presets are adjusted so a client can do desired "tweaks" but return to calibrated settings by selecting a reset function. A preferred calibration may provide separately calibrated user selections for daytime and nighttime viewing. 5) Adjust the color decoder or color matrix for accurate operation. The adjustment will be possible for the NTSC and component video inputs only if color decoder controls are provided in the service menu.
More Detailed Procedures Here is a more detailed calibration step procedure to help you gain a better understanding: Black level setup: Brightness control is set to make the black parts of the picture dark without losing any of the darkest gray picture detail. A calibration product such as the Sencore VideoPro generator provides a special Pluge pattern that alternates a large, open rectangle between black and blacker-than-black video signal levels. This makes it very easy to precisely adjust the black level. First, set the user brightness control to its midrange position. Then, adjust the sub-brightness control in the service menu high enough to be able to see the alternation between black and blacker-than-black. Finally, adjust the sub-brightness back down, just to the point that you no longer see the difference between black and blacker-than-black.
A properly calibrated display provides a standard reference level of brightness, contrast, color, tint and, picture enhancements.
Peak white level setup: The contrast control should be set to produce the highest white level possible, without degrading the picture. The contrast control is often set so high that the picture quality is severely degraded. To calibrate a display's peak white level, first set the user contrast control to its maximum position. Then, adjust the sub-contrast control in the service menu for best picture quality. The user won't be able to push the white level too high and impair the picture. On CRT-type displays, excessive white level causes out of focus blooming, picture bending and yellowing of peak white parts of the picture (the blue phosphors run out of steam first). The VideoPro generator's Needle pattern allows you to detect any of these picture impairments so you can adjust the sub-contrast control as high as possible, without degrading the picture. On fixed-pixel displays, excessive white level causes the brightest gray detail to blend together with full white parts of the picture, called white compression. The VideoPro generator HiLoTrk pattern contains very bright gray boxes on a 100 percent white background, making it easy to detect white compression. Increase the sub-contrast control until you see the brightest gray box just start to blend into the background. Then, back off the control setting one or two steps to insure no white compression. Grayscale tracking adjustment: You should calibrate the background "canvas" color of the display (what you see with the color disabled) to be the industry standard white reference (D65), so that all other colors are reproduced accurately when they are overlaid on the neutral background. This background color needs to be correct across the entire grayscale, from darkest gray to brightest white. Most displays provide two sets of color balance controls. These allow you to white balance the background at a fairly dark gray and at a medium-white gray. Once these two luminance levels are balanced perfectly, there should be very little color shift from the desired white reference at other luminance levels. The three color controls used to balance the dark end of the grayscale are typically called cutoff controls. The three color controls used to balance the bright end of the grayscale are typically called drive controls. To adjust grayscale tracking, you will use a video generator, such as a Sencore VideoPro, that provides a centered white window with adjustable light levels (0-100 IRE). You will use a colorimeter, such as the Sencore CP5000 Color Analyzer, to measure the color balance of the light output and tell you how to adjust the red, green and blue cutoff and drive controls to balance the display's light output to the standard white reference color. White balance the dark end of the gray scale, with the cutoff controls, at a very low light level. This is important, because the human eye is most sensitive to grayscale color shift in the very darkest parts of the picture. Set your Window pattern to whatever IRE level produces about 0.5 foot-Lambert on the display you are calibrating. Adjust the red and blue cutoff controls to balance to the D65 standard white reference color, usually leaving the green cutoff control untouched, as your adjustment reference. White balance the bright end of the gray scale, with the drive controls, at a medium-gray light level. Set your Window pattern to 70 IRE and adjust the red and blue drive controls to balance to the D65 standard white reference color. Repeat the cutoff and drive adjustments a couple of times, to minimize interaction between the two sets of controls.
A colorimeter (Sencore CP5000) measures the light output and tells you how to adjust the displays red, green and blue cutoff and drive controls for a 6500 degree color temperature.
Color and hue adjustments: First, set the user color and hue controls to their midrange positions. Then, adjust the sub-color and sub-hue controls in the service menu for proper color reproduction. Select the SMPTEBar color bar pattern and view the pattern through a blue filter. Adjust the sub-color control, in the service menu, to produce equal intensity in the adjacent white and blue sections of the test pattern. Adjust the sub-hue control, in the service menu, to produce equal intensity in the adjacent cyan and magenta sections of the test pattern. Color decoder adjustment: The display's color decoder is usually adjusted at the factory to over-emphasize red picture coloration, to somewhat compensate for the excessive showroom blue that they want in the background grayscale. After you calibrate the grayscale to the D65 industry standard, you should also adjust the color decoder back to accurate operation, if color decoder controls are provided in the service menu. After you adjust the user controls for accurate blue saturation and blue hue, adjust the color decoder controls for accurate red saturation and red hue, and green saturation and green hue. The VideoPro generators provide a special DecodAdj pattern that makes it easy to calibrate these color decoder controls. Color decoder controls are often labeled R-YR (red saturation), R-YB (red hue), G-YR (green saturation) and G-YB (green hue). Some midrange Sony displays have an AXIS adjust, instead, that gives you four preset color decoder adjustment conditions. Simply choose the AXIS setting that yields the most accurate color decoder operation. If color decoder controls aren't available, you will have to compensate for the red push (over-saturated reds) by decreasing the user color saturation control somewhat, judging the effect on the faces on assorted program material. This, of course, de-saturates all the other picture colors as well, yielding duller looking pictures, making a good argument for calibrating the color decoder, if possible.
A properly calibrated home theater display: · Displays a sharper focused, full resolution image. · Shows full detail in both the darkest and brightest parts of all scenes. · Is properly matched to the video system and the viewing environment. · Maintains the same accurate color balance in both picture lowlights and highlights. · Produces a full range of accurate colors, including flesh tones, grass, sky, and sports jerseys. · Produces a "film look" comparable to 35mm pictures or cinema theaters. · Displays film qualities as the cinematographer intended. · Minimizes picture artifacts (distortions). · Is easier on your eyes. · Lasts up to twice as long as a display with factory default settings.
Calibration Makes Good Business Sense It makes good sense! If you currently offer video services or installations, professional display calibration fits right in. Here’s why.
By offering professional video display calibration you can: · Increase your profits on installations. · Provide repeatable top quality installations. · Differentiate yourself from your competition. · Increase your customer referral base. · Create recurring revenue with yearly calibration schedules: · Promote your company as the technology leader in professional video services.
Professional Calibration Equipment VP403 ‘VideoPro’ The VP403 ‘VideoPro’ Multimedia Video Generator generates the video signal outputs you need for testing, calibrating and servicing any video display type.
The ‘VideoPro’ Multimedia Video Generators produce high quality video signals giving you confidence in your calibration with the video bandwidth required for testing HDTV displays to their full performance capabilities. The generators provide all HDTV formats for testing a video display in all operating modes. The VP403 Generators provide innovative test patterns for determining a video display’s performance and making quick adjustments including Linearity (circles), Pluge, Color Decoder Check, Color Decoder Adjust and more.
The VP403 Multimedia Video Generator is handheld, portable and battery operated so you can service, test and calibrate video displays wherever the job takes you. The VP403 delivers DVI, ATSC RF, standard RF, component video, S-video, composite video and computer monitor signals for all of your display testing needs
CP5000 ‘ColorPro’ The CP5000 All-Display ColorPro is a portable color analyzer for calibrating all video display technologies including DLP, LCD, plasma, CRT and more. The CP5000 calibrates front and rear projectors as well as direct view displays.
The easy-to-use graphical interface greatly decreases calibration time with easy-to-follow measurement screens. The CIE and RGB screens make calibrations simple by illustrating exactly which colors need adjusting. The portable, operation of the CP5000 makes it easy to align displays on location—in the home theater. The performance specifications of the CP5000 mean you can calibrate video display anywhere with lab grade accuracy. The specifications of the CP5000 are NIST traceable. The CP5000’s custom software lets you download calibration data to a PC for documentation, data storage and report generation.
After calibration, you get the sense of being at a local movie theater while enjoying your home theater. Proper video calibration is relatively easy to perform, and the payback for both your client and yourself can be substantial. Don’t let viewers say, “What is wrong with this picture?” Learn more - VP400 VideoPro family: http://www.sencore.com/vp400/index.htm Learn more - CP5000 ColorPro: http://www.sencore.com/products/cp5000.htm
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