Grayscale Calibration of Home Theater Televisions

With the onset of larger TVs and Rear Projector TVs, many Home Theater Systems are as good as movie theaters, and sometimes, even better. As more and more consumers enter into the TV market, it's obvious that the widescreen Rear Projector TV (RPTV) is becoming king. What many people don 't know about TV's in general is that they require calibration in order to produce a close to accurate representation of the video signal being displayed. Many of the new TV's have fancy user menus with all the adjustments one can handle. But fundamentally, these adjustments do not aid in creating a balanced picture, especially when it comes to setting grayscale, which is the basis of most TV calibrations. In fact, user settings such as hue, color, picture and contrast, have little to no effect on grayscale calibration at all. They simply move the entire luminance uniformly within the gamma scale, but these settings do not adjust the CRT's individual outputs as required for grayscale calibration. Yes, you'll see a difference in the way the picture appears from one extreme to another with these user settings but rest assured the grayscale calibration remains unaltered. Interestingly though, the inverse statement is not true. Calibrating the grayscale by using the service menu can greatly improve the TV's ability to produce black and white accurately while improving the contrast, as explained later on in this article.

What is Grayscale?

Grayscale is the result of all three video channels within a display device having the correct gain and bias settings such that an accurate display gray from black to white can be produced at or near 6500K. In a nutshell, calibrating a TV's for accurate grayscale helps ensure that black images are as close to black as possible and white images are as close to white as possible without the intrusion of unwanted colors. Lastly, by calibrating the grayscale, it allows the CRTs (or LCD or DLP or Plasma), to operate closer to the optimal levels where their luminance is as close to D65 or 6500 Kelvin, thus prolonging operating life. Many TVs from the manufacturer are set with red much higher in the dark band and blue much higher in the lighter band of luminance, but this should not be mistaken as the also common "redpush."

Some very important information to understand prior to learning more about grayscale is as follows:

1) Grayscale does NOT effect how the TV will produce color on color images. This is a common misconception that even I was guilty of prior to my ISF Training. Grayscale calibration only effects how the TV produces black through gray to white. Therefore any color in the grayscale should not be misinterpreted as "redpush" or "bluepush" as both of these parameters are color related.

2) D65 is not the same as 6500 Kelvins. D65 is simply a reference point within the black body curve of the CIE color chart that stands for Daylight 6500K. It's coordinates are exactly placed on the chart at X = .313 and Y = .329 which is said to be "daylight." But how many different "daylight's are there? Sunsets, sunrises, pollution, clouds......all effect what we perceive as "daylight." Or as Joel Silver puts it, "How many different shades of white are there?" So a TV can be producing 6500 Kelvins at specified IRE windows, but not be performing at D65 for that window. Instead, there is an actual band along the black body curve where performance can be measured at 6500 K, but not point to X.313 and Y.329. This "zone" is known as the Isotemperature line .

3) IRE stands for International Radio Engineers and it is a relative scale, NOT an absolute . It defines the volt peak to peak video divided up into 140 IRE units. This is done to make numbers for luminance levels easier to communicate. In the ISF Training Manual, it is described as the amplitude of the video signal from blanking (zero volts) to peak white is 0.714286 volts or 100 IRE units. Synchronization signals extend from blanking to -0.285714 volts or -40 IRE units.

• Picture Black Level: 7.5 IRE (above zero volts)

• Picture White Level: 100.0 IRE (above zero volts)

• Blanking Level : 0.0 IRE (zero volt level)

• Burst Pedestal : 0.0 IRE (zero volt level)

• Synchronization : -40.0 IRE (below zero volts)

4) K means Kevlins and NOT degree Kelvins. It is an absolute measurement where 0 K means -273 degrees C.

5) Adjusting the cutoff (CUT) is the same as adjusting the bias, and adjusting the drive (DRV) is the same as adjusting the gain.

Keep in mind that no TV is perfect and therefore getting near perfect performance is next to impossible with most commercial TV's.

Grayscale is more than just black and white. Gray in RPTVs for example, are actually created by the three primary CRT's (blue, green and red). These CRT's are set perfectly such that they are blended to create gray. Ideally, when viewing grayscale images, the CRTs are all operating at around the same temperature range, preferable 6500K, and interlaced (or progressively scanned) together to create the black and white representations. If one or more CRTs gain is too high or the bias is too low, the grayscale images will actually show color variations on some of the grayscale windows. For most TVs, the grayscale appears with a reddish tint at the lower end between 0-IRE to 30 or 40-IRE and a bluish tint between 50-IRE and above. This can be the result of one or more of the CRT's having too high or too low a gain or bias. But don't mistake this as redpush or blue push as these two problems are a result of the hue and color settings. By adjusting the correct gain and bias within the service menu, it is possible to improve the grayscale representation on a TV. The result assures that the TV will not only create better black and white images, but since the CRT's are operating closer to their optimal levels of 6500 K, it may prolong their life.

How to Calibrate Grayscale

There are a number of ways to calibrate the grayscale of a TV. It can either be done by eye or by measuring the light from the TV with a color meter (Spectroradiometer or Tristimulus Colorimeter). Whatever the method, it will involve using the service menu and requires an understanding of how to navigate through a vast array of numbers and symbols along with knowledge on what parameters to change and which to leave alone. Please note that the service menu of a TV should only be accessed by a trained technician.

Many front projectors are hitting the market now that allow access to these type of service menu adjustments via a remote control that allow for easier navigation through the "service" menu adjustments. But even with this, calibration still requires an understanding on the terminology and what these parameters will effect as any adjustments could result in either an improvement or degradation.

So what's the moral of the story? As always, "Don't Try This at Home." What's important to walk away with after reading this article is not HOW to calibrate, but more importantly, WHY. The "how to" portion should be reserved for the custom installer who is hopefully ISF Certified with proper training and therefore knows what he's doing. This article can be used by you to make sure you hire a good technician and can communicate in his language.

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The most common method of calibrating a grayscale first requires the use of the correct grayscale window images. This can be created with a video generator, or using Ovation Software's AVIA Guide To Home Theater . Avia is an all-inclusive DVD that not only helps calibrate grayscale by providing grayscale window images, but also helps with other video calibrations with an added bonus which includes a vast array of audio calibration test tones. There is a tremendous advantage to using a DVD Test Video for the grayscale generation in place of a video generator. The video generator is great for calibrating grayscale with an HDTV signal, but the DVD allows a real world application where the player and TV can be calibrated together.

When using Avia DVD, the process is relatively simple. You navigate through the menus of the DVD to select the correct grayscale window which range from 0-IRE (black) to 100-IRE (white). In a dark room, with minimum lighting and resulting reflections, you carefully go through each gray window from black to white, and use your eyes to see if the image appears to be gray or have color intrusion. The most common color intrusions seen are red in the darker images and blue push in the lighter images, but please remember this is NOT Red Push or Blue Push. Red Push is related to color and hue, not grayscale. While in each window (black to white), it may be easy to see colors bleed through. If colors are visible, you access the service menu and adjust the correct setting to reduce that color. In some cases, colors may need to be increased in order to make gray look gray. While this process if effective and helps improve the TV's performance, it's not nearly accurate enough to achieve 6500K or D65 as it is more guess work then science. Even the best eyes can not detect enough to determine if the settings are near 6500K as our eye can not accurately detect almost drastic differences in the luminance of bright images such as white.

Calibrating Grayscale using Instrumentation

A more accurate way to monitor and adjust grayscale involves using a sensor and its accompanying software. Two well known companies that provide sensors and software packages include Sencore and Milori. Both have their advantages and disadvantages and can be thought of as almost equal in performance. As most good quality sensor/software packages are out of the working-mans price, it is critical to be sure that the technician you hire uses products like these, or they will likely NEVER achieve optimal performance. It is also critical to use these products in controlled lighting in a room as dark as possible. These sensors are very susceptible to light intrusion which will compromise the measurements. So that tech either needs to be in a very dark room with no windows, or they will be at your house very late an night.

Milori's products were used for the basis of this article. Milori provides two different sensors which includes their EyeOne spectroradiometer, or Trichromat Colorimeter, both operating with Milori's ColorFacts software. Sencore provides a similar Colorimeter Sensor with their CP5000 and ColorPro Software. Either of these packages are an essential tool for trained technicians who make a living doing Home Theater installations and/or calibrating TVs. These sensors hook up to any PC via a USB port and their accompanying software runs in Windows.

What's interesting is that ColorFacts lets you decide how the grayscale images are created; you can choose to have the computer generate the images, or you can generate them externally using a test disk like those on the Avia DVD. There are pros and cons to each method.

Using the ColorFacts Grayscale Wizard

The powerful Milori ColorFacts software package contains a host of wizard menus that guide you through set up of the sensor, taking measurements from the TV and reporting results based on calibration images displayed on the TV. It even has its own grayscale generator that works automatically with the sensor. Just one click, and ColorFacts starts grayscale images from 0-IRE to 100-IRE in 10-IRE increments, and at each increment, it automatically measures the resulting luminance. In a matter of a few minutes, you have a complete read out of the entire luminance spectrum of the TV. While using Colorfacts built-in gray scale test images may be the easiest method, it may not be the best suited for your system. This is because the signal generated by the computer may not match the signal generated by the home theater DVD player or HDTV receiver. For more accuracy, you should consider generating the patterns externally using a test DVD. The Grayscale Wizard is best used for calibrating the display monitor on your PC, not necessarily your RPTV or Front Projector.

Using the DVD Player to Generate Test Images

For me, the primary reason for calibrating the TV is to create the best image possible especially for component video input from my DVD player. The DVD player coupled with the Avia Guide To Home Theater creates a powerful image generator tool that works extremely well with either the Sencore CP500 or Milori CF6000 systems.

When dealing with DVD players, it's important to note that the output signal generated from a DVD player varies from model to model. For this reason, calibrating the grayscale using a player will be somewhat unique to the player used in the calibration. If another DVD player is substituted in the system, the grayscale image may be slightly different. Regardless, there is an advantage in using the DVD player for the grayscale source. By doing so, you are actually calibrating the system with the very source that you will be viewing DVD movies, thus allowing for optimization of the Home Theater System. There is a word of caution however. Many of the newer DVD players have video enhancer's built in. These enhancer's tend to exaggerate colors. Prior to calibrating, be sure to turn off the extra enhancement modes as they will create inaccurate results.

When using DVD as the source, the ColorFacts wizard guides the user through the Avia Guide To Home Theater menu to find all the grayscale images required. This method is a bit more tedious and requires special attention as you navigate through the grayscale images on the DVD player and use the PC to activate the sensor and take a reading. If you're not paying attention, you may accidentally hit the sensor button on the PC without changing the grayscale image on the DVD player, thus making you have to start all over again. It's also worth noting that the darker images take the sensor longer to measure then the lighter, so the wait time between selecting grayscale windows will vary. Ovation Software's Guide To Home Theater is somewhat challenging to navigate because this version does not display chapter and title. Nevertheless, when time and caution are taken, this proves to be a more accurate method of measuring grayscale.

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When the full grayscale has been measured, the ColorFacts software displays the results in a number of easy to understand graphs as shown below.

0-IRE        20-IRE                                                                100-IRE

The image above is a final plot of the RGB (Red, Green, and Blue) levels. Unfortunately, this JPEG image doesn't reveal the graph values very well, so I've also marked critical x-axis values. The x-axis of the graph is the luminance ranging from black (0-IRE) to white (100-IRE). The y-axis is the luminance value with the middle of the graph as 100% (optimal), upwards graphs up to 200% (too much) and downwards to 0% (too little). The TV used for this test is the Sony KP-57WV600 after the CRT modification that stopped the flicker (as discussed in the Sony RPTV review

). The results show the green level is at exactly 100% between 20-IRE to 100-IRE, the red is approximately 80% from 20-IRE to 100-IRE (just a bit too low by 20%), and the blue is approximately 150% from 30-IRE to 70-IRE with a gradual decrease to about 120% thereafter. What's important to point out is the results from 20-IRE and below. Most sensors are not able to accurately measure this range, especially in the blue. There simply isn't enough luminance for them to detect. It's not until you get into the high end $20k liquid cooled sensors that you can accurately measure this range. For this reason, measurements from 20-IRE and below should be ignored. The reason ColorFacts shows them is because this software is also able to support a variety of sensors including the high-end units that cost tens of thousands of dollars. The upcoming release of ColorFacts will allow you to start the reading from any value, so you will not see the effect of the inaccurate low-light reading. The interesting parameter adjusted related to blue which required drastically reducing the bias from 30 to 1.

What's encouraging about the graph of measurements from this RPTV is the red bleed in the whiter part of the spectrum has been eliminated. The first graph (not shown) on this RPTV was not even close to 6500 K and set in the red zone of the CIE chart. Prior to adjusting the RCUT (bias) level in the service menu, the red bleed through was about 150% which was far above 6500 K. The final graph above is a result of changing the RCUT or red-cutoff (which is the bias adjustment for the red CRT) in the service menu from 38 to 29. Other modifications that resulted in the graph above included increasing the green bias (not gain - you can increase bias without changing gain) from 41 to 43 as this color needed a boost in order to approach 100%. I was unable to detect the green was low by eye alone. It's only by measurement that I was able to determine the correct setting.

Several attempts were made to change the BDRV (which is the gain adjustment) to a lesser value in hopes to reduce the blue blled. While a blue bleed between 120% to 140% is typical with most RPTV's, the original value of 150% is excessive and could reduce the longevity of the blue CRT. The original BDRV value on this RPTV was 41 and was decreased substantially to almost 20. Although the blue output is not as linear as the red and green, it is an improvement that is noticeable on the white grayscale windows. It seems this particular model Sony RPTV had the blue CRT performing way too high, thereby creating very inaccurate grayscale representation.

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Another useful ColorFacts graph includes the full display of the RPTV performance on the CIE Chart shown below.

This chart displays how the CRT grayscale is tracking through the color spectrum. The black line represents 6500 K along and is known as the Black Body curve. Although this curve does not show it, the isotemperature line also defines 6500 K but not necessarily along the black body curve. It can be thought of as a broader width along the curve, but does not assure it is on this curve. Furthermore, D65 is a specified point at Y313 and Y329, not just 6500K.

The large dots display actual measurements of the performance curve of the RPTV using the grayscale images. Early plots of this RPTV showed points all over the place. After adjustment, the points are much closer together and are tracking near the black body curve along 6500 K, but are NOT at D65. Further tweaking and the use of other test gear was required with different measurements in order to adjust performance closer to D65.

What's extremely important to note is that that the eye alone is not able to detect these subtle changes and allow proper adjustment which provides this kind of accuracy. Even the best technician with the most experience can not do this without a sensor and software, as explained in the section on the last page regarding the eye.

It's not only a fact, but I know because I tried. When I set the CUT levels and DRV levels by viewing the grayscale with my eye alone, I was far off the mark. In several instances I thought I had the correct setting and after measuring, it was still off. I was surprised to learn how much difference changing these settings just one point value made after measurement, even though my eye could not detect a change to the grayscale window. So be leery of hiring a technician who doesn't have some form of measurement gear if not by Sencore and Milori, then at least another trustworthy manufacturer. Feel free to research test equipment prior to asking what gear your technician uses and don't be afraid to ask them for specifics on their gear along with serial numbers.

Other ColorFacts Results

Another nice feature about the ColorFact software by Milori is that it provides a graphic interpretation of the results compared to the ideal black body curve.

This graph compares the actual measurement values (in yellow) to the ideal settings near 6500 K (dotted white) so you can determine how close to 6500 K your TV is performing. After changing the service menu items listed above, this TV is now accurately tracking along the luminance curve between 100-IRE and 50-IRE. Below that point it dips down some, which may also be a function of stray light which may have interfered with the measurements at these lower IRE settings.

There are many other useful features found in the ColorFacts software including continuous sensing, contrast measurements, and reports. All these tools can be used to measure the TV's performance and help in adjusting the correct values and settings. Furthermore, at the end of each grayscale measurement, ColorFacts wizard asks if you would like to file a report, and if so, if it's an initial measurement or final measurement. When you file the report for both, the end product shows the graphs of the before and after on a neatly formatted page that is stored as a .JPEG file. Don't be afraid to ask your technician for a copy of the post and pre calibration measurements.

After Gray Scale

Upon completion of the grayscale calibration, I realized my work with this RPTV was far from over. For starters, changing the voltages to the CRT's through the service menu settings affected the convergence. It is therefore necessary to carefully and patiently conduct a three point convergence after adjusting the grayscale. The Avia DVD shows test patterns for convergence, but this is really only good for showing you how far off the convergence really is. Many newer TV's have an easy to use user menu two color convergence where the user can converge two of the three colors manually with the TV remote. The user menus for convergence do no allow the green CRT to be adjusted. Doing a convergence with the user menu is a fairly good representation of a convergence, but it is not the most accurate. The newer TV's also have service menu convergence where you can do a full three point convergence on a more refined level, but once again, save this type of work for the pros as you can do more harm then good.

One thing worth pointing out is the TV's with the automatic convergence, or self convergence is based on the three point convergence done within the service menu. Without first calibrating this convergence pattern, the automatic convergence will do little in adjusting the actual convergence of the TV. Once again, this is no place for the common man and should be left to a technician. But be aware that it is another MUST DO part of calibrating, especially Rear and Front Projectors that have CRT's.

Setting Picture and Brightness

After grayscale and convergence, it's time to refine the picture using some of the user menu functions. The Avia Guide To Home Theater DVD actually does an outstanding job of explaining how to adjust picture and brightness, so I won't go into any detail here. The one thing worth pointing out is that after using the test images from the Avia DVD, the final settings will be surprising. The overall tendency is to have the brightness turned up on RPTV's that are in light rooms. This compensation comes at the price of picture quality. After using the Avia test images to adjust the settings, the picture will not appear as bright as before, but it will be a more accurate picture with improved detail.

Color and Hue

There are two key things worth mentioning in this section. Early in this article, I stated that color and hue adjustments via the user and service menus do not affect grayscale. To prove this, use the AVIA DVD and display several grayscale windows. Then play with the color and hue to see if these windows change. Grayscale helps produce better black and whites (or grays), not color. Therefore, it is important to adjust the color and hue in order to ensure that the performance of the TV in color is also accurate.

The Avia DVD has additional useful patterns which help adjust the color and hue. Hue and Color adjustments by eye are challenging, but with the blinking squares found on the Avia DVD, it's a snap. When viewing this image through a blue filter, the blinking squares should disappear and the blue should appear uniform.

As a personal testimony, prior to calibrating this RPTV, I was never able to make the blinking boxes go away. But after using a tricolorimeter sensor and operating software and carefully adjusting the hue and color, in a matter of minutes I was finally able to make the blinking boxes disappear. However, it did require another round through the service menu, this time altering the color filters which included RYR, RYB, GYR, GYB. Notice how there is no adjustment for blue itself. Instead, it is common to adjust the blue using the user menu color and hue and a blue eye filter to make the blue portions match. From there, it is a trip through the service menu and use of the red and green eye filters while carefully adjusting up and down the green and red with respect to blue. Eventually, all the blinking boxes will disappear with the appropriate eye filter.

Closing Comment on the Eye

The eye is not a perfect machine thus the reason for a sensor. But the sensor isn't perfect either. Below 20-IRE most sensor measurements should be avoided. The sensors are not able to see low luminance light and in addition, outside light will virtually corrupt any real measurement even if it could. Grayscale calibration is best complete using both the eye and a sensor. What's interesting is that our eye sees variations of color extremely well and in most cases, better than sensors. But it does not see details in color very well. In addition, the eye sees detail in black and white extremely well, but not variations in black & white. For example, when viewing the 100-IRE (white) window, you can literally double the output (12000K) and not really notice much of a difference in brightness.

Black and White

If you're an adamant black and white movie lover, take note of this. If you have a front projector that allows two different calibration level's to be stored, consider having your tech guru setup and store another grayscale setting using E65 as the standard instead of D65. E65, also on the black body curve, has a slightly different XY coordinate and was the standard used for filming old movies. Therefore playback using E65, even though it is a slight change along the curve, makes a HUGE difference on display of B & W movies. When calibrating to E65, these movies appear more vintage looking and in some cases, even show more definition and detail. I now understand the reason why so many photographers still take black and white images. As explained in the section above, we see more detail in black and white than we do in color. If our TV is properly calibrated for B & W, the amount of detail can be significantly improved.

The True Test

I've had the Sony KP-57WV600 for over a year now. I even had friends who are trained ISF technicians come and help me calibrate the TV by eye alone on several occasions. It's not until after my ISF Training and using a sensor and software that I was able to enjoy the fruits of my labor. It's an undisputed scientific fact that the eye alone can not detect the performance levels required to make the necessary grayscale adjustments, but it will detect the improved performance and refined detail that comes when viewing DVD's. After completing the grayscale adjustments, three point convergence, picture/brightness adjustments and color/hue calibration with the Avia DVD, the true test began.

My personal favorite DVD for showing picture quality is by far, "The Lord of the Rings." This DVD has impeccable video quality. My favorite scene used for testing video performance is just after the introduction when Gandalf comes on horse and wagon to meet Frodo. At the start, there is a scene where Frodo is sitting against a tree and a scene just after when Gandalf is coming down a path on the wagon. I've watched these scenes countless times to try to see differences after adjusting the TV. After calibration with test equipment, I finally see significant improvement. In these scenes, the tree bark, for starters, is much more detailed and almost three dimensional. Then there is the scene where off in the distance you can see sunlight beams clearly defined and outlined between the trees. The sunbeams are much more noticeable with finer detail then before. After adjusting the RYR, RYB, GYR and GYB, the color accuracy was also noticeable as Frodo no longer looks like he's wearing makeup as skin tones appear more natural. Beyond "The Lord of the Rings," I previewed Pixar's "Monsters Inc." and Disney's "Finding Nemo." Perfection, or at least close to it, had been accomplished

Conclusion

This goes to show that having the right tool for the job is extremely valuable. For most, having calibration equipment around the house may be both impractical and unaffordable. I can appreciate that not many will want to purchase a $2,500+ measurement package to adjust a $1,500 TV. But it is worth considering having a professional TV calibration completed by someone who has this type of equipment and knows how to access and navigation through service menus. What I learned form my ISF Training was that there is logic to this calibration method that should be followed in order to maximize performance. For these reasons, we suggest hiring someone who has been ISF certified as it will end up being worth the extra money. We've found too many TV Technicians that know little or nothing about grayscale calibration, and unless they have been properly trained and have the correct gear, they can do more harm than good. Several things to note when searching for a technician to calibrate your TV is as follows:

1) Have they been trained to calibrate using proven methods - ISF is certainly one possible training and certification

2) Will the provide both the pre and post calibration data?

3) Do they understand Convergence, how to set brightness and contrast, Color Calibration using hue and color as well as service menu features, and Grayscale Calibration using bias and gain?

4) Is their measurement equipment licensed? If so ask them to verify this.

5) Be ready to pay some good money. Someone who knows how to calibrate, has been trained, comes over at night, and has measurement equipment, may charge $150 per hour. They also charge per input, so make sure you know how many inputs you want to use.

6) Remember, Grayscale is only one part of calibrating your TV. You also should do color, hue, contrast, three-point convergence and on the list goes, which were briefly covered at the end of this article. The more you ask the technician to do, the more you'll spend. If you're in a bright room, and don't watch too many DVD's or HDTV then don't go the extra mileage. If you are into video as much as audio, then calibrate everything you can as it will make a difference.

7) Most TV's have different calibration settings for standard inputs (Satellite, DVD, ...) and HDTV inputs. You should have your technician do both. While the Ovation DVD's should be used for calibrating your TV to your DVD player, a video generator should be used to provide the grayscale, color, hue, contrast images for HDTV. Do NOT use a DVD and up convert it. Unfortunately, there are no HDTV calibration images being broadcast on HD channels at this time, and your calibrator WILL need a generator, such as the Sencore Video Pro Generator .

Stay tuned as very soon, we will have links to ISF certified technicians who may be in your area.