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| The LT-47899 had pretty strong color performance; the color temperature was fairly uniform and the colors curves were reasonably smooth. However, the green component was rather inaccurate, which could lead to inaccurate greens. |
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Color Temperature (6.51) 
You might assume that white is white, but you'd be wrong; the color of white on a display is determined by something called the color temperature. This is a rather complex issue, but the bottom line is that a display should have an identical color temperature whatever the intensity of the white on the screen. However, displays seldom have this, so we test how the color temperature varies as the intensity of the white on the screen varies, going from the brightest white right down to nearly totally black. As part of our calibration process, we calibrate the TV so that the color temperature of the brightest white is as close to 6500k as possible (which is the same as daylight), then test how this varies as the intensity of the white decreases. An ideal TV would have a flat curve here, but the LT-47X899 didn't have that; particularly at the darker end of the curve, the color temperature got significantly higher, which means that some pale grays could look rather cool and slightly bluish. However, it is worth pointing out that for the majority of the curve, the difference is not enough to be noticeable by most users; it's only at the very low end of the range that the slight error creeps in.
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Another way to look at this is to plot the measured color values of the different intensities, which is below. On this graph, all of the the measurements of the different intensities of white (shown by the black line) would be on the same spot. The red line indicates the smallest change in color that is perceptible by the human eye; if the line stayed inside the red circle, you would not be able to see the change. But the line goes outside the circle, indicating that some people with good eyesight might be able to spot a very slight blue cast to the low intensity whites.
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RGB Curve (7.73)
To analyze the performance of displays such as the LT-47X899 in more depth, we also analyze the red, green and blue components of the display. All displays use red, green and blue to create the colors you see on the screen, so it is important that these are accurately represented. In particular, our tests look at how well the display represents the range of colors for each of these primary color components, going from black to the maximum color intensity. Our testing produces this graph, which shows the intensity of the input color signal (from 0 to 255) along the bottom, and the intensity of the resulting color on the screen along the side.
The critical factor here is not the height or shape of the curve, but the smoothness of the curve. A bumpy curve indicates that the display is not rendering the color accurately; bumps and jumps are a sign that there are issues with the way the display processes the color behind the scenes and then displays it on the screen. These could lead to inaccurate colors and even artifacts such as banding, where a gradual change in color becomes a sudden one, creating a visible band of color in subject such as blue skies and subtle foliage. The LT-47X899 has some issues here; the red and blue curves show distinct stepping, which makes them look more like elevator steps than a smooth curve. This stepping leads to problems such as banding and fringing because subtle color changes get lost, and we saw evidence of this on our tests with a variety of test images; a sunset had a rather grainy look, and some colors had a slightly flat, artificial look to them.
Color Gamut (3.59)
The color gamut is the range of colors that a display can reproduce, based upon the three primary colors (red, green and blue). There is a specific set of recommendations for this that were defined by color experts which detail the gamut of colors that a HDTV signal should contain (called Rec.709, short for the ITU-R Recommendation.709), so we measure how closely the range of colors that the display can reproduce matches this range. The results of our tests are shown below; the dotted line indicates the recommended gamut, and the solid line is the gamut that we found on the LT-47X899. An ideal display would have exactly the same gamut as the recommendation, with the solid and dotted lines overlapping. The dots in the middle are the D65 white point, and again on a perfect display, the two dots would be right on top of each other.
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As you can see, the LT-47X899 has a mixed result here; the red and blue edges of the gamut are a little bit away from the ideal, and the green (at the top) is significantly off. This would mean that greens would be inaccurate; pure greens in particular will look slightly unnatural as the colors are pushed further out into the color gamut than they should be. Again, this was borne out in our test images; on this TV, foliage looked darker and deeper than it should, and other greens had a distinct color cast to them.
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