BFI / MPA : what is really going on

BFI / MPA: what is really going on

This system might be surprising at first if you have never heard of it. This configuration obviously has nothing or not much in common with the BFI described by BenQ in their data sheets. It is however very close to Samsung’s MPA technology.

The screening on the BenQ monitor

The Korean manufacturer described it at the last CeBIT and presented a 24" monitor based on a PVA panel. The principle relies on the introduction of an artificial screening by successively shutting down neons located behind the panel. The similarities are striking, aren't they? So what should we think about this VA monitor, so similar to the one developed by Samsung? There are several possibilities. People at the origin of the technical documents could have misinterpreted the information, AU Optronics could have surprisingly changed their opinion, or the third possibility is that this would be an adaptation of Samsung technology at the expense of the one developed by AU, which might have been delayed.

Either way we aren’t talking about a complete MPA, and it includes a second part that is absent from the current BFI (can we still use this name?). Samsung monitors are clocked at 120 Hz. The images received at 60 Hz are duplicated twice for a refreshing frequency of 120 Hz instead of 60 Hz. Another subtle difference is that BenQ uses the time when a segment is black to begin making part of the next image. The objective is that the user won't see more afterglow from the faster rate. Area switched on: image 1. One of the 16 segments is switched off. During this period of 1/60 Hz /16 neons = 1 millisecond, the monitor begins to draw image 2 and erase the previous one. The backlighting is switched on and if reaction time of the liquid crystal was high enough, image 2 would have been drawn and the previous one erased. In fact, this response time of 1 ms is a little bit short regarding the liquid crystals currently implemented in the panel. It can slightly diminish the afterglow sensation due to the higher rate, but it can't erase it completely yet.

Here now is the functioning as we have understood it (we have to say here that no one at BenQ confirmed these points, their official version still involves black frames):

The monitor is divided into 16 horizontal areas of 75 lines, with a CCFL tube behind each area. T is the time measured.

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At T=0, the processor shuts down the first area, the highest one, and leaves the 15 others with the image displayed.

At T=1, area 1 is still dark and the processor searches in the monitor’s memory for the piece of the next image, sending the display command to the liquid crystals.

At T=2, the crystals display the image or are finishing the second image, the processor switches on the backlight in area 1, and turns off area 2.


The loop consists of drawing a piece of the image on a dark monitor, drawing the next slice in the dark, turning on, shutting down the area below, and so on. Once the area 16 is drawn, the area 1 is switched on and the next image is drawn.




This is a progressive type of display. Each time 15 of the 16 areas are switched on while one is in the dark. As we have seen above, each area is in the dark for approximately 1ms.

For now, the fraction of second is often too short for the drawing of the next image to be made in the dark. However, it can already minimise afterglow due to the change from one color to another and in intermediary color scales.

Let's take the case of a monitor with a maximum response time of 16ms, with a 8ms rise and 8ms fall time. If we wish to change one area from red to blue, and if the rise and fall were linear, the dot displayed would show the following colors:


In fact the curb followed by each color isn't linear. It looks rather like this:



If we follow the time transition, colors change like this:


Before the dotted line are the colors displayed during the first millisecond. The black square shows a monitor with a rise and fall time of 8 ms, whose colors transitions will happen in the dark. In our example, rotation no longer starts with a pure 100% red, but rather with a 25% red and 25% blue. Afterglow should be reduced.

BFI in practice: games

The BFI in practice

We might be afraid of two things due to the introduction of this innovation:

- a significant loss of brightness
- variations in the homogeneity of brightness.

Unfortunately, our fears were confirmed.

One good point, however, is that the afterglow noticeably diminished once the BFI was activated and the improvement was obvious. We estimate that it was cut in half, however, we are also sure that some of you won't activate it in games. Why? Because the screening at 60 HZ might be too disturbing for some. In fact, you end up having to choose between the lesser of two evils. Is it better to have a slightly blurred image or rendering that twinkles? After a few days of gaming, we found that this depends on the game. Some have rather homogenous images (strategic games, for example) and the screening of the black area could be disturbing. In this case, we preferred playing without BFI and fortunately, this is where afterglow is the least disturbing. We don't need perfect reaction time for this type of game and we can make do with a slight blur of the image when units are moving.


Then there are FPS, in which the character is always moving. Here, we weren't disturbed by the neon switching on and off. However, if you are a "super demanding" user, you won't be able to play with the BFI activated and you will regret buying this monitor. Don't concentrate on this point too much. Play your games and then adapt the monitor to your use, perhaps adjusting the BFI intensity (three levels are available in the OSD) according to your perception after one hour of gaming.

Reaction time test

A car moves from left to right at high speed.

Movement isn’t perfectly fluid. Depending on its speed, the car is shown in several successive positions. If the car goes very fast, the positions are very close and the eye perceives a flowing movement.
Perfect monitor monitor with 3 ghost images
A monitor without ghosting effects would have previous images completely fading away when a new one appears. This is the theory and in practice, it's often not the case as images fade progressively. Sometimes up to 5 afterglow images remain on the monitor and represent the visible white trail behind objects. Some monitors have strong overdrives in addition to image anticipation algorithms. In this case, an image can appear in front of the main object, creating a white halo ahead of objects in motion.

With CRTs we captured afterglow with a camera at a shutter speed of 1/60 seconds as compared to 1/1000 s for an LCD. We take 50 pictures per test. We then can see a monitor’s ghosting effects, or all the car’s position in the entire process. The most important image is the one on the left, the better one. It will be the most displayed on the monitor, while the one on the right is in transition.

Here are the two extreme states with each monitor as afterglow oscillates.

BenQ FP241WZ, PVA 6 ms with BFI activated at 3

BenQ FP241WZ et FP241W, PVA 6 ms wihtout BFI.

Dell 2407WFP, S-PVA 6 ms

Afterglow in pictures is unchanged in all three monitors. This proves that the BFI doesn't have an impact on the reaction time of pixels. The BFI has an impact on our eyes, more specifically, on retinal persistence.

Color rendering and movies

Color rendering quality

If we want to even talk about color rendering, you have to deactivate the BFI. For office use, it only has negative consequences. If you look at a single color background in Photoshop, for example, it is clearly possible to perceive the screening. This is unbearable due to the occasional twinkling especially when you have left the CRT world. The activation of the BFI makes you see black spots. Deactivate it!

BFI has a considerable impact on monitor brightness. If when deactivated brightness was approximately 250 cd/m², with BFI activated (level 3), it falls to 105 cd/m². If you use your monitor for different uses, you will regularly have to go through the OSD to activate or deactivate BFI and adjust brightness and maybe contrast. If as usual, the two parameters are a bit mixed up when one is modified, for an accurate image you will have to work with both of them.

Here, we have deactivated BFI and started our test procedure:


This is disappointing for a so new panel. We started to get used to having accurate colors from the start. Here the gaps measured are rather significant and superior to Samsung's panels produced for about a year now. You can readily see the differences in the greys here before and after calibration. We reconstituted this scale according to the figures measured:


It is possible to get better results by making some manual modifications. Look at the ideal grey below and the one displayed above by the monitor. We quickly see that there is a grey dominance. You can correct it manually in the OSD and for more precise colors add a bit of green.

Be aware that if you choose this version of the monitor without the Z, the FP241W, the color dominance will be quite different. This is really surprising as we were expecting identical color tables: the FP241W has a red dominant.

Movies

- This is a PVA panel, which produces strong twinkling effects in all color scales. It’s much higher than that of MVA 8 ms panels. This makes us regret that BenQ hasn't chosen this AU Optronics technology.

The AMA-Z has advantages and downsides. In terms of improvements, its activation noticeably reduces afterglow. We estimate that it is cut approximately in half. The other thing is that it’s best not to have scenes with a single color in the background or else screening and homogeneity differences may be noticed.

Conclusion

Conclusion

What a surprise! Between theoretical and practical tests, there is an enormous difference. We were expecting a technology designed by BenQ and we have found a derivative of an innovation first presented by Samsung. As a reminder, Samsung hasn't released this technology yet and the first MPA monitor is scheduled to be released in 2007. Until this date, we will have to make do with this 24".

Now, if you find this technology really interesting because you want to reduce at all costs afterglow that is too much of a problem with other monitors, we recommend you wait for the MPA that will have another advantage, a 120 Hz mode. The combination of "high frequency" + "screening" will probably give excellent results and we can't wait to see it! Unfortunately, no manufacturer has announced a release date for these products. Do we really have to wait for one?

What about the HDMI input?

We almost forgot about it and we have to say that we haven't been really convinced by its results.


We made several tests with the DVI input of our graphic card, the HDMI input of the monitor and a very good cable (very expensive) connecting the two. No luck, the monitor was no longer recognised in its native resolution, 1920 x 1200 pixels, but rather as a TV, and was restricted to 1920 x 1080. The image was still fully displayed (it wasn't cut as it sometimes happen with TVs) but it wasn't sharp. Interpolation was problematic, which often happens for computer monitors. It introduces a slight blur effect and a noticeable reduction in details.

We used this interface for a couple of minutes to test it, but we quickly went back to DVI

Conclusion: we like the ergonomics, good reaction time and innovative aspect…

Lastly, we spent a lot of time discussing the technology and haven't talked about the monitor ergonomics, design and finishing touches. First, the finishing touches are rather average. Compared to the 23 and 24" monitors of the competition (Dell and Apple, for example), the BenQ looks a bit cheap with its basic plastic and very standard design. It compensates with the video inputs (HDMI, YUV, S-Video), the USB hub of 3 ports (two on the left side and one above), the vertically adjustable foot and pivot mode. This monitor is extremely practical and very pleasant to use.

Finally, we come to the price and release date. The BenQ FP241WZ is scheduled to be released in January 2007 at 1,009 € (VAT included). The version without BFI will be at 1,049 €. If you buy one of them, choose the Z version.