Grayscale Calibration of Home Theater Televisions - page 4

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.