Grayscale Calibration of Home Theater Televisions - page 3
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.