Panasonic Viera TC-37LZ85

Color Temperature (5.71)
Any HDTV needs to display an array of whites from bright white to dark greys. In this test we look at how stable those whites are in terms of color temperature. Ideally we want the color temperature to stay around 6500 kelvin across the range. If the temperature rises too high you get a bluish cast and if it falls too low you get reddish casts. Below is a chart showing the color temperature of whites on the Panasonic TC-37LZ85 across the greyscale.

You can see that across most whites the color temperature stays pretty stable, but especially as you get into the darker greys the color temperature skyrockets. It's not uncommon to see this happen with darker greys, but the effect is significantly more pronounced with the Panasonic TC-37LZ85 than we've seen on other HDTVs. In order to see how significant this problem is we also want to know whether the humany eye can actually make out the changes in color temperature.

That's what we look at in the graph above. Here you see the color coordinates of each white graphed onto a color space. The red line indicates the point the range within which the human eye can't tell the difference. Thankfully the Panasonic TC-37LZ85's whites almost all fall within this circle, as we would expect as we saw only a small amount of deviation across most whites. Those that fall outside the circle, however, are pretty far out there. What this means in practice is that the Panasonic TC-37LZ85 will display a strong bluish cast as you start getting into darker greys, much more pronounced thant we've seen on other HDTVs. It's this that produces the Panasonic TC-37LZ85's rather mediocre score in this test.

RGB Curve (7.06)
All colors you see on your HDTV are produced by combining three basic colors: red, blue and green. Each pixel on the screen is actually made up of these three colors. As such the accuracy with which the HDTV can reproduce these colors is critical in producing accurate colors overall. Below you can see each of the three colors graphed across all intensities for the Panasonic TC-37LZ85.

Ideally we would like to see smooth and slightly concave curves for all three. You can see that although green and blue do a decent job with this the reds show a noticeable hump across the mid range of intensities. We could see the effect of this innacuracy when we looked at a scene with a lot of reds and noted that we lost a lot of detail in these mid tones.

The other thing we look for is peaking. Some HDTVs stop being able to reproduce actual differences in colors as you get to higher intensities. You can see this on their graphs as a plateau at the end of the curve. You can see from the curves above that this isn't a major problem with the Panasonic TC-37LZ85. Overall the issue with accuracy in the reds does drop the Panasonic TC-37LZ85's overall score a bit, but it's not the worst we've ever seen.

Color Gamut (0.0)
All HDTVs are supposed to reproduce colors in the exact same way, using an international standard color gamut known as ITU Recommendation .709. This ensures that content producers can be sure that the colors they want reproduced on the screen will be reproduced accurately across all displays. Below you can see the Panasonic TC-37LZ85's color gamut graphed against this standard.

You can see that the Panasonic TC-37LZ85 has some significant problems, especially in the reds, but even greens and blues are slightly off. What this means in practice is that some colors on the display won't come through in the way that the original producer wanted them to be seen. The Panasonic TC-37LZ85's performance in this test is actually about average, which says more about the generally unimpressive color gamut performance amongst HDTVs than it does anything good about the Panasonic TC-37LZ85. Below you can see a table with the exact color coordinates and error for each of the points of the color gamut triangle as well as the white point (D65).

	u' (rec.709 / tested)	v' (Rec.709 / tested)	Error
Red	0.4507 / 0.4671	0.5229 / 0.5227	0.016401219
Green	0.125 / 0.122	0.5625 / 0.5681	0.006352952
Blue	0.1754 / 0.1727	0.1579 / 0.1626	0.005420332
D65	0.1978 / 0.1948	0.4683 / 0.4665	0.003498571