Secrets Product Review
 

Epson Home Cinema 1080 LCD 1080p Projector

Part III

October, 2007

Steve Smallcombe

 

 

On the Bench


Calibrations in the 1080i mode were performed using an Accupel HDG-3000 Component Video Calibration Generator, a device capable of generating video calibration test signals in a wide range of video formats. I also used a Toshiba HD-XA2 High Definition DVD player for DVD viewing with a 1080p output, as well as watching HD and standard definition material in 1080i with my DISH ViP622 PVR.


Measurements


When I evaluate a projector, I not only look at images, but also measure the color balance of the projector at various light intensity levels and determine the quality of what is called Grayscale Tracking. The idea is that black, white, and all shades of gray, should have the correct ratio of the three primary colors used in video projection Red, Green, and Blue. You can read more about the testing method in my past projector reviews in Secrets, at http://www.smartavtweaks.com.


Using the Digital Video Essentials HD DVD, the proper brightness level was seen to be 0, the default value, but with the default contrast setting of 0, there appeared to be some compression of levels just below white. A setting of -2 showed these levels properly. Color decoding seemed fine with the default settings.


I then switched to the Accupel signal generator to check grayscale tracking, starting with a Color Temperature setting on the HC 1080 of 6500K.


To check the absolute color balance of new projectors, I typically compare the light from the projector displaying an IRE 50 to 70 grayscale window with light from my reference D65 light source, a SolSource lamp from GretagMacBeth. This lamp not only has a color very close to D65 (D65 defines a unique point in the CIE color space, whereas 6500K defines a line), it also has a very similar spectrum to daylight, and therefore makes an excellent reference to compare with projector-generated light. By this comparison, the projectors 6500K setting was lacking in green. Measurements with SMART also suggested that while the color temperature was about 6150K, the light from the projector was definitely shifted away from green and towards magenta from the target D65 coordinates. I found that this could be largely corrected by boosting the Skin Tone level, but decided to use the RGB Offset and Gain controls instead, as they would allow more flexibility in tweaking overall grayscale tracking. Therefore, I increased the Green Gain control so that the projector's light better matched the color of gray from the D65 light source.


The measurements below were made with these settings for color balance and the Theater Back 1 setting for Color Mode, and with the Auto Iris Off, and Gamma set to 2.2, the default setting.

 


As can be seen in the Color Intensity chart above, the HC 1080 color balance was well behaved through the entire range of IRE input levels or Percent Stimulation.

 

 

The Color Balance Graph above shows the same data, but in this case, plotted as a ratio between the various colors. The ratios shown in the Color Balance chart do a much better job of showing details at the lower input values, and in this case that there is a bit too much red and not enough green at the mid to lower input levels.

 

 

Lowering the Red Offset control and raising the Green Offset improved the grayscale tracking as can be seen above.


The ANSI contrast ratio with the projector so adjusted, was 420:1. The light intensity at my 92 inch diagonal 1.3 gain screen was 16.1 ftL with the Brightness Control in the Low setting and 20.7 ftL with the Brightness Control in the High setting. ANSI lumens were calculated to be 309 and 397 respectively.


Gamma Tracking


The other thing we measure is Gamma Tracking, or how the light output of the projector responds to the input signal. If the projector's Gamma Tracking is off, then details in the image will either be lost, or the image may look flat and have little contrast. The Gamma Tracking graph shows the combined light intensity at the various input levels relative to a theoretical level. If the projector is accurately producing the intended light intensity level as a function of input or IRE level, all values should be close to 1 in the gamma tracking graph.

 

 

In the Gamma Tracking graph above, we can see that the Epson HC 1080 has accurate gamma tracking through the low to mid input levels, relative to the intensity levels calculated for a target gamma of 2.2. This graph also shows just a bit of compression at high input levels. Note that this graph, as all measurements above, were made with the Auto Iris off.


Measurements with Auto Iris On


The Epson HC 1080 is equipped with an Auto Iris feature intended to improve black levels and contrast ratios. The advantages and disadvantages of an Auto Iris will be discussed below.

 

 

The graph above compares the light output of the projector with the Auto Iris on (Black) and off (Yellow). Note that the measurements compare the light intensity of a small IRE window displayed in a black field. From this graph one might conclude that the Auto Iris feature had little effect of the projectors light output, which is largely true at high input levels. The problem however with graphs that show output light intensity vs. input levels is that details of the behavior at low input levels are lost. (This is why I always show gamma tracking as a ratio of the measured output level to the theoretical or calculated levels for a given target gamma rather than as a graphical comparison of light intensities.)

 

 

By displaying the same data as a ratio of the light intensities of the projector with the Iris on and off, one can clearly see the effect of the Auto Iris feature on the light output for the small IRE window being measured. As might be inferred from the graph, use of the Auto Iris had no effect on the overall brightness of the image at high input levels, but improved the black levels by almost a factor of six. As a consequence, the measured contrast ratio with the Auto Iris on was 2,570:1. As one would expect, measured color balance and grayscale tracking did not change with the Auto Iris function on.

 

 

With the Auto Iris on, Gamma tracking, when displaying small IRE windows at least, was reasonably well behaved with an overall gamma of 2.2.

 

Go to Part IV.

© Copyright 2007 Secrets of Home Theater & High Fidelity

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