Our TV Picture Quality Tests  

SDR Color Accuracy

The white balance Delta E, or dE, determines how accurately a TV can display shades of gray from white to black. You'll notice inaccuracies with the white balance the most with large areas of white or gray colors, like if you're using it as a PC monitor or if you're watching sports like hockey and basketball. White balance is extremely important, as the human eye is actually far more sensitive to grayscale than it is to colors.

We measure the white balance from 5% gray (nearly black) to 100% gray (pure white) in increments of either 5% or 10%, depending on what the TV supports in its white balance settings. We calculate the average of the inaccuracy for all the shades.

In the above grayscale gradient examples, you can see a fairly dramatic example of how an imbalance affects a particular shade of gray. The 70% and 80% shades on the left both have a good deal more red than they should, and this throws off not only their appearance but also the way they interact with close shades. The grayscale image on the right shows the same TV after a full calibration. The red tint is gone, and the image looks much better.

Interpreting the results is fairly straightforward, as there's a chart on the left that shows the dE for each shade of white from 0 to 100%. The longer the bar, the more error there is. Most TVs will have the most error with shades closer to white because they require the most color (pure white is a combination of red, green, and blue), while error with darker shades is less common. The graph on the right represents which colors are the most inaccurate for each shade of white. You may notice that some TVs have more bars than others. This is because some TVs only allow us to calibrate the white balance in steps of 10%, while others support 5% steps. The number of measurements we take is determined by the number of steps supported by the TV.

The color dE measurement expresses how accurately a TV can reproduce the following colors: Red, Blue, Green, Yellow, Magenta, and Cyan. Generally, if a TV can reproduce these six colors accurately, the overall color accuracy for the rest of the color tones will also be good, so this is relatively consequential.

To evaluate color dE, each color is displayed on a window in the center of the screen and displayed at points of 25%, 50%, 75%, 95%, and 100% saturation, with a 75% stimulus, and we also measure pure white. The different levels of saturation show how well the TV displays the color at different shades; a 100% saturated red is different from a 25% saturated red, which is closer to pure white.

The resulting measurements are then displayed on a CIE 1931 xy chromaticity diagram. These plots aren't perfect, as they only look at a single slice at a fixed luminance, so some TVs could perform better at lower luminance levels. This is why we've moved towards gamut rings for SDR color volume measurements instead. For the purposes of measuring color dE in SDR, though, this approach is still acceptable.

Gamma is the ratio between the light and dark areas on your screen. In other words, if the gamma is off, the image either looks too bright or too dark. Unlike the white balance and color dE, a gamma that's a bit off is easier to notice. We measure the gamma using a series of gray levels from 0 to 100% gray, so it's measured at the same time as the white balance. We measure the gamma for each shade of gray, and we get a resulting graph for all the different shades.

The target gamma is 2.2 across all scenes, represented by the yellow line in the graphs above. The gray line is the TV's measured gamma; if it follows the yellow line, it has a perfect gamma. If it's above the yellow line, scenes are too dark, and if it's below it, scenes are too bright. Again, the final result in the review is the average, so even if a TV tracks well on average, it could still be too bright or too dark in certain shades. It's quite common for TVs to push bright parts of the scene a bit brighter than they should be, for example, as it delivers a slightly punchier image.

You should also note that our gamma target of 2.2 isn't the only correct gamma. TVs typically have several gamma options available, usually ranging from 1.8 to 2.6. Our target of 2.2 is about in the middle and is targeted for darker rooms. Apart from 2.2, a gamma of 2.4 is also appropriate for very dark rooms, and a gamma of 2.0 works pretty well for brighter ones. Most TVs also offer BT.1886, which is a variable gamma standard that's designed to better preserve dark scene details on LCD TVs. Below you can see examples that showcase the impact gamma has on the image. Unlike the white balance, color dE, and color temperature, gamma isn't currently scored as part of the overall color accuracy score.

The color temperature of a TV has to do with color accuracy. A warm color tone means that the colors are shifted more towards red than blue, and a cool color tone has colors that are closer to blue. Like the other tests, this test is measured automatically using the CalMan software.

Color temperature is one aspect of picture quality that almost anyone can notice, even if it's slightly off, and this makes it one of the few settings that you can usually adjust manually with no specialized equipment. Most TVs have a fairly accurate color temperature out of the box, but it's not uncommon for TVs to be a bit warm by default.

The current industry-standard 6500K represents the most accurate white point and was designed to match midday daylight. While it's designed to deliver a very neutral image, if you're used to something colder (or warmer), you may want to change this setting to something that looks better to you. The lighting in your room can also have an impact on how you perceive color temperature.

Above, you can see a clear example of how the color temperature directly impacts picture quality. Most people will find the one on the right to deliver a more natural-looking image, even if it is a bit on the warm side.

Our post-calibration evaluation is an overall score for the quality of a TV's picture quality after a full-color calibration has been done. This score will give you an idea of what to expect from your TV if you do plan on getting a calibration done. That said, most TVs end up having about equally accurate color once calibration is done, so these scores aren't quite so important. This test is more about the process itself and determining how well the TV can be calibrated.

We calibrate the TV using the 2 and 10 or 20-point white balance settings, depending on what's available. Some TVs don't have as many calibration settings, so it's harder to calibrate for the most accurate image possible. Other TVs can't be calibrated too aggressively, as fixing one issue might introduce another, so in that case, we try to calibrate it as best as possible without causing other problems. Also, we avoid extreme adjustments whenever possible. Ideally, the closer each adjustment is to zero, the better. Very aggressive calibrations can result in color banding.

In the post-calibration tests, we once again measure the white balance dE, color dE, gamma, and color temperature. In the settings page for each review, you can see which settings were used for the full calibration. Because each panel performs slightly differently, we don't suggest using our calibration values for your unit.