If you remember the review of the 23″ Planar SA2311W 3D monitor I did not too long ago, you should also remember the interesting effect I’ve observed in the photo above (the banding on the white color). After testing a more recent model, namely the 27-inch Acer HN274H 3D monitor I have also observed the same strange effect with my extreme stereo 3D crosstalk test photos…
The photo above is of the monitor showing the 3D test photo and not through the lens of the shutter glasses, so don’t use it to judge for level of ghosting as it is not intended for that, but it is to investigate the strange gradation of white I’ve noticed. This test 3D photo uses black on white for the two eyes as this makes the strange color gradation of the white to be most apparent and it turns out that this issue is somewhat related to the OverDrive function as well as the current level of brightness (the contrast setting) of the monitor. If I disable the OverDrive through the system menu the problem with the gradation of the white disappears, but in turn I get a lot of crosstalk which is to be expected. If I push the contrast setting (the brightness) of the display higher or lower there is also difference in the banding of the white with the white turning out to be completely even after a specific value.
Of course the black on white stereo 3D crosstalk test photos are an extreme case that should not normally happen in real world use scenarios or it will be very hard to be seen with normal stereoscopic 3D content displayed on the screen. Nevertheless I wanted to know exactly what is causing this strange behavior, how exactly it is related to the use of OverDrive and why it was not present in the previous 3D-capable LCD monitors that I’ve tested already. So I’ve been in contact with Planar to get the answers to this questions and they were very helpful in explaining the exact reasons, also confirming my observations regarding the OD and contrast settings. I’m going to quote the exact response I’ve got from Planar below:
I’m going to try to explain why banding can be seen with certain stereo test patterns on Planar’s 3D Vision monitor. First, the goal of stereoscopic visualization is to show the left image only to the left eye and the right image only to the right eye. We want to prevent residual of the left image showing up when the right image is displayed, and visa-versa. Because lines addressed near the top of the display have more time to settle than lines at the bottom of the screen, the display electronics need to drive pixels more aggressively to switch from left to right as you get closer to the bottom of the screen. The display electronics has some limitations, where it can’t change the “aggressiveness” on a line by line basis. There are finite steps that the current drive electronics can control. This causes the banding, which can be seen on test images with constant gray values in one eye and high contrast in the other eye. However, as you stated in the article, this artifact is difficult to see in normal stereoscopic images because you would very rarely have large areas of a common gray level with high contrast between the left and right eye. If such an image were exhibited it would be uncomfortable to view (on any 3D monitor) because of the large discrepancy between the two eyes. This banding issue is below the threshold of visibility in real world images; just when guys like you or me test the extremes.
You asked why banding can be seen in test images on the new panel and not on the older ones. The older panels used one overdrive value for the entire display. This resulted in low stereo crosstalk in the middle of the display, but noticeable ghosting at the top and bottom of the screen. The new SA2311W monitor has low stereo crosstalk across the entire screen.
As for the reason that changing the contrast setting can eliminate banding, consider that with a low contrast setting you would drive a normal image from 0 to 85% (for instance) of the range available. This leaves some headroom for LCD overdrive which is used to improve 3D quality by reducing stereo crosstalk. In this case, you would see banding when a black image is shown in one eye and a high gray level (white) image is shown in the other. When you increase the contrast setting, you eliminate the headroom for overdrive. All the white values may be driven near 100% so that banding disappears, but then you observe ghosting. In general, a lower contrast setting results in better 3D quality for normal images.
The bottom line is that the appearance of this strange effect is a result from the efforts being applied in order to reduce the level of crosstalk/ghosting we are getting on the more recent 3D monitors and in order to have less ghosting at the top and bottom of the screen as compared to the earlier models. As it was already mentioned, this strange behavior is observed only with extreme test conditions and should not be easily noticeable in real world usage scenarios. And the white banding in these test photos will most likely be something that we are going to be seeing a lot from now on in the new 3D monitors that are about to come later this year, but you should not be worried about that fact. The important thing is that we are getting less and less crosstalk/ghosting with newer 3D-capable LCDs, right… ;)
The crosstalk or ghosting of images (leaking of part of the image for the left eye into the right eye and vice versa) is a common problem with the current generation of 3D-capable 120Hz LCD monitors with different factors influencing it. One of the common issues is that the LCD panels are still not fast enough in terms of response time and because of that the monitor manufacturers resort to the so called Overdrive function (using more voltage to drive the pixel change state faster) in order to increase the pixel response rate. This works to some extent, but may as well lead to other issues like burnt colors resulting in colored ghosting visible in stereo 3D mode for example. Another common cause for ghosting is having brighter colors on darker backgrounds or vice versa, especially if the separation between the left and the right eye is higher. And then again there is the so called top and bottom ghosting that represents more ghosting on the top and at the bottom of the screen that is usually caused by not so good timing with the image on the screen and the shutter glasses. And since I’ve been trying different methods of reducing ghosting lately, here comes another effective solution that can help you reduce the ghosting when playing in stereo 3D mode with an Acer GD245HQ or Acer GD235HZ 120Hz LCD monitors. The solution is based on custom modifying the color temperature levels of the monitor from the Service Menu that is usually not available to the normal user, but you can call it if you know how to do it. The good news is that the same method might also work with the ViewSonic VX2268WM (I’m already working on that, so stay tuned), but will unfortunately not help the owners of the Samsung 2233RZ as the Service Menu of that model is not so good in terms of additional controls available.
Lets get back on the Acer. For the following examples I’ll be using a short demo video shot by the user 3D Frank shared over at Nvidia’s 3D Vision forums that is a great example for ghosting, you can find a download link at the bottom of the post if you wish to try it on your monitor. Have in mind that the following ghost reduction method works not only when watching stereo 3D videos, but also with 3D photos and when playing games in stereo 3D.
And here is how you can call the Service Menu on the Acer GD245HQ / GD235HZ:
– Turn off the monitor
– Press and hold the first menu key (the leftmost one)
– Press the power button while still holding the 1st menu key
– When you see the image on the screen you can release the menu key
– Press the third menu key (the middle one) to call up the Service Menu
– Navigate in the service menu just like in the normal one, but now all options are changeable
– To return back to the normal mode just turn off the monitor and turn it back on the normal way
Lets me start with how the display looks by default when showing a stereo 3D image and you are not looking through the shutter glasses. The blue menu in the top left corner is the service menu that is showing the default options for the display, as you can see the Overdrive (OD) function is active and on the screen you can practically see doubled images of the boats and burnt out colors of the most bright white on the sailboats.
When you put on the glasses instead of doubled sailboats you’ll start seeing ghosting which looks like shadows as you can see on the picture above taken through the right lens of the shutter glasses. Again here we still have the Overdrive function of the display active.
Now lets see how the things look when the Overdrive function is disabled. Without the shutter glasses on the image still looks doubled, but there are no burnt colors. Other than that no significant difference can be noticed with the named eye…
Overdrive is still disabled, but now looking through the glasses you can see significant difference in the image as compared to looking through the shutter glasses with the Overdrive function enabled. Instead of just some shadows the ghosting here is so severe that you still see doubled objects, although a bit more faint than when looking without the glasses. This is just to give you an idea of what can happen when the response time of the pixels is not good enough and why monitor manufacturers are using Overdrive on the LCD panels.
Now comes the fun part. I’ve decided to use the Cool temperature preset available in the Service Menu to modify in order to reduce the ghosting. So the new settings that I’ve defined for it are 100 for Red, 90 for Green and 85 for Blue. Although I’m using the Cool preset my settings are warmer because the Red color is higher (you can decrease it to about 85-90 to get cooler temperature), but I prefer the Warm color temperature and this makes it easier to compare it with the default Warm preset.
After doing the tweaking of the Cool preset from the Service Menu of the monitor you need to turn off the monitor and then turn it back on normally to get to the normal monitor menu, where you need to select the Cool preset in the Colour Temp settings in order for the things to work and you to have less ghosting. You can cycle between the Cool and Warm color presets to see the difference, the Warm preset should have easily noticeable color ghosting while the custom Cool preset should have hardly any visible ghosting.
And so how does the tweaked settings look like in terms of ghosting, you can see in the picture above taken through the right lens of the shutter glasses. There is hardly any visible ghosting left, although if you look up close and carefully you may still notice some very faint traces, but that should not bother you when using the monitor normally as it is hardly visible anymore.
Before and after this tweak you can try a game like Tomb Raider: Underworld with a separation of lest say 50%-100% (depending on how much you can handle) in order to have high separation and to compare the ghosting. You will however see that there is still some top monitor ghosting, it seems unaffected as it is probably caused by synchronization timing issue whit the shutter glasses and that is why the above tweak does not affect it. Still the end result where you don’t have burnt colors, color ghosting and almost no ghosting at all is completely worth it if you ask me, so if you own an Acer GD245HQ or Acer GD235HZ monitor I recommend you try my tweak and report your results in the comments below.
And just one more thing I’ve noticed about the Acer while playing with the “ghostbusing” settings in the Service Menu of the monitor. When you turn on the monitor and immediately display a stereo 3D image you’ll most likely see more ghosting, but after 2-3 minutes the visible ghosting gets reduced a bit. This means that it probably takes a few minutes for the electronics in the monitor to start working at its best with the Overdrive function performing optimally…
– Download the Sailboats Ghosting Test – mirror 1