Sharp Aquos LC-46D64U LCD HDTV Review - Performance: Color

Mixed is perhaps the best phrase to use for the color performance of the LC-46D64U. Although it had clean whites and good response for the primary colors, we found that the colors were slightly inaccurate.

Color Temperature (9.88)
Putting white on the screen of a HDTV isn't as simple as you might think; because the display has to create the white from the three primary colors it can display, there can be problems if the three different colors don't change at the same rate. That's what we test for here, looking for any issues with the whites at different intensity levels having a color cast. The graph below shows the results of our tests: the intensity of the signal (from the brightest white at the left to nearly black on the right) is on the bottom axis, and the color temperature is on the side axis. As part of our calibration process, we set this to as close to 6500k as possible (to simulate daylight), and the line on the graph shows any variation from this.

The variations are very small for most of the way; the graph only shifts slightly from the initial setting. But it goes a bit crazy at the bottom end of the intensity scale, with the whites taking on a distinctly bluish cast. Another way to look at this is to plot the measured color values of the different levels, which is what we do on the next graph. On this graph, the color of the white for the maximum intensity is at the center of the graph, and the dots indicate the color of the whites at different intensity levels. The red circle indicates the color shift that the human eye can detect; if a dot falls within this circle, you aren't going to be able to see the a color change. But if a dot falls outside of the circle, you might be able to spot the color shift.

Again, you can see that quite a few of the dots fall outside the circle, although the majority are nicely within the circle limit. This means that for most intensities of white, the LC-46D64U has good, consistent whites. But with low intensity whites (such as shadow details), the color of the white shifts towards the blue. However, this shift is limited to a small part of the range, and should not be an issue for most users.

RGB Curve (6.64)
All TVs make the colors you see on screen by mixing the primary colors; red, green and blue. They do this by turning on and off the red, green and blue elements of the screen, and your eye does the work of combining the colors to make the required color. To create an area of yellow, for instance, the HDTV turns on the red and green elements. More subtle colors are created by turning on the elements gradually; a more orange-yellow can be created by turning down the intensity of the green. In order to accurately reproduce colors, HDTVs need an accurate response to each of the primary colors; if a slight change in intensity in the incoming signal doesn't translate into a slight change in the luminance of the color on the screen, colors are not going to be accurate. So, we test the response of each of the primary colors, and the results are on the graph below. On these graph, the intensity of the signal is along the bottom, and the resulting luminance is along the side.

These graphs have some issues; they are a little bumpy and have slightly different slopes. The bumps indicate that the response of the HDTV is not smooth; there are points where the response suddenly jumps, and issues like this can cause inaccurate colors and color banding. This is where a subtle change in color (such as a blue sky) becomes a sudden one, and we saw some evidence of this in our tests with sample images on the LC-46D64U; some images had distinct, unattractive color banding.

Color Gamut (4.7)
An international group of experts has defined a set of guidelines on the limits for what colors a HDTV signal should contain (called the Rec.709), and a good HDTV should match those limits. So, we test this by looking at what the color gamut of a HDTV is. This is shown on the graph below; the dotted line is the limits set in the recommendation, and the solid line is what we saw from the LC-46U64U.

The blue and red corners of the gamut are pretty close to where they should be, but the green is a little bit off, with the gamut edge being shifted towards the blue. This could cause some colors to look inaccurate; bright greens in particular will look a little bluer than they should. For the hardcore color space fans amongst you, the chromaticity values of the colors are in the table below.