 |
| The Vizio VO47LF had mixed results here; although the whites on the screen were very bright, the blacks were not particularly dark. This means that some images will lack impact, and that your dark and frightening horror movies may not scare your pants off. |
 |
Black Level (4.78) 
Deep blacks on the TV screen mean that your movies look good; there's nothing worse than the dramatic scenes of your favorite film noir turned into a grey goo because the display can't produce a decent black. The VO47L had fair to middling performance here; we measured the deepest black at 0.44 cd/m2 (candelas per square meter, a measure of luminance where lower is better), which is in the middle of the pack; several displays that we have tested have had deeper blacks. The Panasonic TH-46PZ80U, for instance had a much deeper black (0.06 cd/m2) and the JVC LT-47X899 had a slightly better black (at 0.37 cd/m2).
Peak Brightness (8.47)
The flip side of the coin is how bright the whites are, and we measured the VO47L at an impressively bright 313.8 cd/m2, which is pretty damn bright. Brightness is only part of the performance of a display, but it is an important part; more brightness means that the display will be more visible in bright daylight, making it more suitable for daytime use. The VO47L had no problem here; over 300 cd/m2 means there is plenty of screen brightness. If you rally want to crank it to the maximum, you ca gnet it to 395.47 cd/m2 by pushing up the brightness and contrast controls, but this is not recommended; it has a serious effect on the color accuracy of the display.
Contrast (5.52)
The relationship between the black and white is the contrast ratio; it gives a good indication of the range of shades that the display can manage to produce. We measured the contrast ratio of the VO47L at 713:18, which is a decent, if unspectacular ratio. Because they had better blacks, several other displays had better scores here; the Samsung LN46A750 had a significantly higher contrast ratio of 2842:1. But the VO47L is comparable with other similarly priced displays; the JVC LT-47X899 was only slightly higher at 830:1.
One thing to note here; our figures are different from the contrast ratio figures quoted by the manufacturer (such as Vizio's 2000:1 for the VO47L) because they measure the ratio between the dark with the backlight turned down, and the brightest white with it turned up (sometimes called dynamic contrast). We measure the contrast ratio with the backlight on the highest setting, so our figures are usually much lower than the manufacturer quoted ones. Our figures are more representative of the performance you would see in the real world, though.
Tunnel Contrast (9.42)
The tests above are done with just whites or blacks on the screen, but that's not what displays have to work with; real images are composed of a mix of blacks, whites and lots of bits in between. And some displays have issues with this; the light from the white parts of the screen leak into the black bits, making them lighter (see the animation on the right for an example). To see if displays have this issue, we test what is called tunnel contrast, where we measure a small area of black in the middle of the screen with different amounts of white on the screen. The graph below shows the results of this test; the amount of white on the screen is on the bottom, and the luminance of the black area is on the side axis.
 |
 |
As you can see from this, the luminance of the black did not increase much, even when they were surrounded by white; the last point on the graph (at the right side) is for the screen with 95 per cent white, so only a small area of black is on the screen. Even with this extreme example, the brightness of the black was only slightly up from when there was little white on the screen.
White Falloff (9.65)
Some displays have a problem with white; if there is too much white on the screen, they turn the brightness down so they don't overheat (plasma displays are especially prone to this). So, we look for this by measuring the luminance of the screen with different amounts of white on the screen. The results are shown below; the amount of white is on the bottom axis, and the luminance of that white is on the side.
As this shows, there were no issues here; the luminance of the white stayed pretty much constant across the range; the whites were the same brightness if there was 5 or 100 percent of the screen that was white. That's good; you'll get the same white if you are watching a gloomy horror movie or a documentary on polar bears frolicking in the snow.
Uniformity (6.3)
The uniformity of the screen is also important; there's no benefit to having the brightest white and deepest blacks if they don't remain the same across the screen. The VO47L again had middling performance here; we found both white and black screen sot be reasonably uniform, but there were definite lighter areas in the black screen, and the corners were somewhat dimmer in the white screens. These issues were definitely noticeable when watching a video, but they didn't detract overly from the image quality.
Grayscale Gamma (9.22)
All HDTVs process images on the screen, and one aspect of this processing is called Gamma. This describes the way that the HDTV converts the shades of gray from the input signal into the different intensities of brightness that you see on the screen, and this transformation can vary significantly from display to display. We test this by feeding a series of screens of varying intensity to the HDTV, then measuring the luminance of the screen. The results are shown below; the intensity of the signal is along the bottom (from black at the left to the maximum intensity at the right) and the measured luminance of the HDTV is on the left axis.
An easier way to look at this test is to plot the data onto a graph with logarithmic axis; because we are dealing with a power sum curve, it should then come out with a straight line. That's shown below, where the black line is the measured curve, and the blue line is the trend. A perfect TV would have teh same curve and trend.
As you can see, the Vizio is pretty close to the ideal here; the curve is flat and ties in well with the trend. Form this we cna also work out a figure for the gamma; we look for a figure for this of between 2.4 and 2.5, and the VO47LF was at 2.33, just a touch outside of the ideal range. But that's close enough that it won't be an issue for most users.
Resolution Scaling (6.6)
The VO47LF is a 1080p display with the full 1080p resolution, but it doesn't always get a 1080p signal to display; many devices output signals in the lower HDTV formats, and the display has to work with these. So, we test how good of a job the display does by feeding it a series of test screens in various high definition signal formats. Let's look at each of these in turn.
480p (6.30)
480p signals are produced by many standard definition devices that have digital outputs, such as high-end DVD players or some standard definition cable boxes. We found that the VO47LF did a reasonable job of working with these; the text in our test screens was sharp and very legible. We didn't notice any significant issues with problems caused by the dithering that the display uses to upscale the image, edges and lines looked clean and sharp. The video was overscanned by about 4 per cent, which is pretty standard for this type of video.
720p (6.5)
720p high definition signals are often used by broadcasters when they are showing sports, as progressive video provides smoother movement than the higher resolution, but interlaced, 1080i. We found that the VO47LF again did a reasonable job here; the images were sharp and clear. Again, the image was overscanned (by about 3 per cent), which is a little unusual: most displays don't overscan 720p images.
1080i (7.0)
1080i video is the most common form of high definition video; it's what most over the air high definition signals are sent in, and it's what most high definition cable boxes produce. The VO47LF did a decent job here too; images were sharp, but the interlacing of the signal was obvious; moving objects had a somewhat jagged look.
Overall, the quality of all of the scaled resolutions was more then acceptable, making the VO47LF usable with a range of video sources.
|
