JVC LT-42P300 LCD HDTV Review - Blacks & Whites

Blacks & Whites Summary
• Unimpressive black level • Plenty of brightness • Dynamic backlight you can't turn off causes problems • Gamma curve too steep causes brightening too quickly • Testing done with DisplayMate software
	Calibration	Page 4 of 16	Color Accuracy

Black Level (5.04)

We had some trouble with the JVC LT-42P300's black level. When we first measured it we got a reading of 0.11 candelas per meter squared (cd/m2), which is an excellent black level for an LCD television. Unfortunately, on further examination, we realized that the LT-42P300 was actually "cheating" to get this black level. What was happening was that when the television realized that the screen was all black it would actually turn down the backlight. Our standard is to measure the black level with the backlight turned up to maximum. As such we used a measure with the screen 90% black, which stayed constant across all but the 100% black screen as you can see in our tunnel contrast test below. This measure was a much less impressive 0.39 cd/m2.

The reality is that you are rarely, if ever, going to be looking at a total black screen when watching content on your HDTV. As such the higher black level reflects the reality of how deep blacks are going to get for the average user. To make sure that this was the case we looked at some very dark scenes on the LT-42P300 and noted that even a nightime scene wouldn't trigger the backlight reduction we saw in our testing. We don't know why the LT-42P300 does this, it could be a power saving feature or it could be for the benefit of people like us and marketers as an attempt to claim a deeper black than the HDTV is actually able to produce in normal use.

Peak Brightness (8.36)

We measured the JVC LT-42P300's peak brightness at 304.16 cd/m2. This is a measure of how bright the screen can get, and as you can see from the comparison graph below it performed significantly better than the JVC LT-32P679, albeit not quite as good as our other two comparison HDTVs. In the larger scheme of things the LT-42P300's peak brightness is above average and should be quite bright enough for almost any user.

Contrast (5.65)

Contrast is the ratio between the brightest white and the deepest black. In the case of the JVC LT-42P300 the contrast ratio is hurt by the unimpressive black level of 0.39 cd/m2 and as such measures only 779.9:1. You can see below that this is the worst contrast ratio amongst our comparison HDTVs. It's also significantly below our average for all televisions. The human eye is very sensitive to contrast so this is an important measure of the quality of the image you will get on your HDTV, especially when viewing high contrast scenes.

Tunnel Contrast (7.64)

In this test we look at what happens to the black level of the JVC LT-42P300 as we put less and less black on the display. You can see here the direct effect of the dynamic backlight feature that we talked about above in the black level section, notice how it starts out much lower when the screen is 100% black then when the amount of black on the screen starts to fall. Once this initial change occurs, however, the black level stays rock solid, which is what we want to see from this test.

White Falloff (2.60)

This is the opposite of the tunnel contrast test, here we want to see how the peak brightness holds up as less and less of the screen is white. Once again you see the effect of the dynamic backligh, which here occurs when when the percentage of the screen that is white falls to 10%, with a remarkable drop in the brightness, which gets even worse when you get to the 5% white screen. This dropoff results in a pretty excerable score in this test.

We thought about how to handle this situation given that we diregarded the effect when looking at the black level of the JVC LT-42P300. In the end we decided that because the feature cannot be turned off and can in fact cause some problems, for example we saw the screen brighten and then dim alternately when looking at content like scrolling credits, that we would leave the score as is.

Uniformity (7.50)

Here we look at how uniform the JVC LT-42P300's display is by looking at both a white and black screen. As is typical of most HDTVs we noticed dimming at the corners with the white screen and overly bright areas at the corners with the black screen. This was the only major problem however, we were happy to see that the center of the screen was smooth and uniform with none of the blotchiness that we sometimes see from other HDTVs.

Greyscale Gamma (6.42)

Gamma is the curve along which a television makes the transition along the greyscale from black to white across the range of greys in between. Below you can see a graph of the gamma curve plotted logarithmically (ie. 10, 100, 1000 etc.) which is how our eyes actually perceive changes in the greyscale. The blue line represents the best fit, and as you can see there are no major deviations from this line on the actual curve, which would indicate  problems.

The JVC LT-42P300's actual gamma was measured at 2.8. This is significantly higher than our ideal of 2.1 to 2.2, and indicates that the television is being more aggressive about changes along the greyscale than we would like. This means that things will get brighter faster, which can cause some scenes to look overly bright or washed out.

Resolution Scaling (8.03)

Although we would love for every piece of content you see on the JVC LT-42P300 to come in full 1080p quality, the reality is that this quality is only available from Blu-ray discs. Most other content will come in either standard definition or a different flavor of high definition formats. Below you can see how the JVC LT-42P300 handled the scaling of each of these formats.

480p (8.80)
This is the quality you will get from DVDs and is standard definition quality. As is common when content is being upscaled from a lower resolution the JVC LT-42P300 had some trouble mapping the pixels onto its display, resulting in about 2% of the screen being lost on all sides, a phenomenon known as overscanning. We didn't have any problems reading text on the display, even small 6.8 point fonts, and there were no issues with resolution or moire patterns.

720p (7.80)
This officially qualifies as high definition content, with 720 lines from the top to the bottom of the display. As with 480p content, however, there were some overscanning issues with 2% of the scene lost on all sides. We also noticed some minor problems with letters running together on small fonts and some more serious problems with resolution as the LT-42P300 struggled to reproduce clearly distinct alternating black and white lines.

1080i (7.50)
The difference between 1080i and 1080p is in the way that the content is scanned onto your television. While 1080p content shows you all the lines of resolution at once 1080i content alternates between two sets of 540 lines. This is the reason why it's most commonly used by broadcast stations as their HD standard since you only have to send half the signal at any given time. Unfortunately it can also produce some unfortunate side effects, and this was the case with the JVC LT-42P300. In particular we noticed a strong green tinging on the display for certain cross-hatched patterns, something that can be annoying as it could show up on many patterns in actual content, for example a herring-bone suit. Aside from that, however, we saw no major issues and since 1080i is the same technical resolution as 1080p there were no overscanning problems.