Samsung LN46A750

Color Temperature (7.35)
You might think that white is white on a television, but it isn't that simple. Instead, the color of white can vary as a display shows different intensities of white, and that's what we look at here. On a perfect display, the color of the white would stay the same whether it is a pale grey or the brightest white that the display can manage. In reality, that doesn't happen; because of the way the display processes colors, the color of white varies slightly, and that's what we test here; how constant the white is. When the color temperature increases, the picture gains a slight bluish hue; when the temperature decreases, it acquires a reddish hue.

The LN46A750 did well here; the shifts in color change that we saw were generally very minor and would not be noticeable by most users; they are just too small. Another way to look at this test is to plot the actual color data, which we do in the graph below. The red circle on this graph indicates the minimum color change that is generally detectable by the human eye, and the dots represent the measured color values.  The bottom line here is that if a dot falls within the circle, you aren't going to be able to spot the difference between the two whites. but if it is outside of the line, you might be able to spot a slight color cast in the white.

As you can see from this, a lot of the points are right on the edge of the circle, while others are outside, veering towards the red, indicating that there are some of the grays that have a slight, but possibly noticeable color cast to them. These errors are generally small, though, and most people won't notice them.

RGB Curve (9.04)
All of the colors that you see on the screen are made of three basic components; red, green and blue, which are created by the individual elements of the display that we discussed earlier. To create colors, the display turns these on to create a color mix. To create yellow for instance, the display turns on the red and green elements. To create violet, the display turns on the red and blue elements. To create white, the display turns on all three. This means that it is vital for the TV to work correctly that each of the primary colors is displayed correctly, and has a good response to the incoming signal. That's what we test here; we look at how the display takes a signal of each of the primary colors at different intensities and translates this into the colors you see on screen. Our tests produces the following graphs that show the curves for each of the primary colors.

On a perfect display, these curves would be completely smooth like a child's slide, indicating that the intensity of the input signal was accurately reproduced; every slight increase in the intensity of the input lead to a similar increase in the intensity of the color on the screen. In practice, the graphs we see tend to look more like a bumpy mountainside than a child's slide, because of the way that the TVs process the images.

The curves for the LN46A750 were very smooth; we didn't find any big jumps, steps or other problems. This means that slight changes in all of the colors are accurately represented, so subtle details won't get lost. And this was borne out with our testing with a number of difficult test images; subjects with lots of subtle color (such as sunsets, skin tones and foliage) looked great; all of the subtle details were visible and well reproduced. Overall, the LN46A750 did very well in this test, producing accurate color across the range of tones. 

Color Gamut (5.03)
Television signals contain a certain range of colors, called the color gamut that are defined in an international standard (called the ITU Recommendation .709). So, a decent display should accurately match this color gamut, and we measure the properties of the red, greens and blues that the TV can produce and match them against the standard; a perfect display would exactly match the standard gamut. On the graph below, the gamut is shown by the dotted line, while the measured gamut from the LN46A750 is shown by the solid line.

For the geeks amongst you, the chromaticity values of the colors are in the table below.

	X (rec.709 / tested)	Y (Rec.709 / tested)	Error
Red	0.4507 / 0.4502	0.5529 / 0.5329	0.0011
Green	0.125 / 0.1157	0.5625 / 0.5615	0.0093
Blue	0.1754 / 0.1757	0.1579 / 0.1443	0.013
D65	0.1978 / 0.1943	0.4683 / 0.4679	0.003

This is a decent result; the measured maximum limits of the gamut only vary from the recommended ones by a small amount on the gren and blue corners of the triangle. The biggest error is in the green, where the maximum extent of the gamut was shifted slightly towards the blue.