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Results: Brightness And Contrast

Asus PQ321Q 4K Monitor Review: Top-Shelf Ultra HD For $3500


Before calibrating any panel, we measure zero and 100 percent signals at both ends of the brightness control range. This shows us how contrast is affected at the extremes of a monitor's luminance capability. We do not increase the contrast control past the clipping point. While doing this would increase a monitor’s light output, the brightest signal levels would not be visible, resulting in crushed highlight detail. Our numbers show the maximum light level possible with no clipping of the signal.

Our comparison group consists of the last six desktop monitors reviewed at Tom’s Hardware.

The PQ321Q slightly exceeds its claimed spec of 350 cd/m2. There is more than enough light available from the display for just about any environment.

Unfortunately, the effect on black level is negative.

A result of .5088 cd/m2 is fairly high compared to the competition. And it is higher than the Planar’s value, even though that screen is almost 100 cd/m2 brighter.

Here’s the final contrast result.

Asus' PQ321Q won’t be sold on the basis of its contrast performance. Since this is our first IGZO-based display, we can’t say if low contrast is inherent to the technology. We currently have Dell’s 4K screen in the lab as well, and we expect to be looking at Sharp’s model soon. After that parade of Ultra HD decadence, we'll know if IGZO gives up contrast superiority to IPS, or if Asus simply made influencing design decisions.

We believe 50 cd/m2 is a practical minimum standard for screen brightness. Any lower and you risk eyestrain and fatigue. Many monitors do measure under that level. While the comparison chart shows the absolute lowest brightness for a given monitor, we also comment on the contrast and black level results at a 50 cd/m2 setting.

The PQ321Q has a maximum output of 49.7378 cd/m2 when brightness is set to zero, which is right at our standard! We’ve been a bit concerned about the trend towards brighter monitors because some of them can’t be turned down to 50 cd/m2, which is preferable in a dark environment. Fortunately, the PQ321Q has enough luminance range to reach both very high and low brightness levels. For these tests, we only turned down the brightness. Black Level and Contrast were left alone.

The PQ321Q’s black level improves mightily when you turn the backlight down. A result of .0729 cd/m2 puts it right in the middle of the pack.

The on/off contrast ratio stays about the same whether the backlight is turned all the way up or down. The image is very consistent in quality regardless of your preferred light level. Even though the contrast numbers are on the low side, perceived contrast is pretty good thanks to spot-on gamma performance which we’ll talk about on the next page.

After Calibration

Since we consider 200 cd/m2 to be an ideal point for peak output, we calibrate all of our test monitors to that value. In a room with some ambient light (like an office), this brightness level provides a sharp, punchy image with maximum detail and minimum eye fatigue. It's also the sweet spot for gamma and grayscale tracking, which we'll look at on the next page. In a darkened room, many professionals prefer a 120 cd/m2 calibration. We find this makes little to no difference on the calibrated black level and contrast measurements.

Hitting the 200 mark on the PQ321Q is tricky because the Brightness control is extremely coarse. Each click of the 30-step slider results in a change of almost 12 cd/m2. After tweaking the Contrast control, we got it to settle at 197.3585 cd/m2.

You’ll want to lower the Black Level control to a point just before detail is clipped. Anything below 28 and you won’t see the darkest steps. We used 30 so we could comfortably see detail in a moderately-lit room.

This is a good but not great result. We are glad that calibration doesn’t seem to cause any penalty in black level. Of course, the changes made to grayscale are small because the PQ321Q has such good out-of-box accuracy. And we do recommend calibration, especially considering the PQ321Q's price. If you’re going to put a $3500 monitor on your desk, it should perform at its absolute best.

Here are the final calibrated contrast numbers.

Again, the PQ321Q’s on/off contrast ratio comes in just under 700:1. Compared to most of the screens we’ve tested, that's a below-average result. At least it has excellent gamma to improve its perceived contrast.

ANSI Contrast Ratio

Another important measure of contrast is ANSI, which we measure using a checkerboard pattern of sixteen zero- and 100-percent squares. This is somewhat more real-world than on/off measurements because it tests a display’s ability to simultaneously maintain both low black and full white levels, and factors in screen uniformity. The average of the eight full-white measurements is divided by the average of the eight full-black measurements to arrive at the ANSI result.

It always impresses us when a display maintains an ANSI contrast ratio close to its on/off one, demonstrating the use of high-quality components, particularly the grid polarizer. Light leakage between dark and light portions of the image is almost non-existent.

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