Yes, but not a great deal. I set for video levels.
Yes, I can faintly see the screen as it is white and as a dedicated projection screen it reflects what light there may be, however small. Also after a few seconds your eyes get used to the environment and it becomes more obvious, even in a bat cave like my room.
You are never going to get a complete lack of light even for black levels, as you are projecting onto a white (or grey surface), so even the best DI on the best possible projector is not going to improve that, imho.
In my black theater room I can sit for a minute with the projector off and not be able to see the screen. I wonder if that along with having a slightly raised brightness may explain that loss of shadow detail and lack of seeing any real improvement with the DI, or whether I would also see loss of shadow detail in my room if I tested that scene (which I can't do at the moment). I really don't know.
I mentioned in a thread here before that one difficulty with a DI is that its purpose is really to lower the light for level 16 without lowering the light for other levels. I'm going to simplify a little bit, but if the projector is setup so that it is treating an input level of 16 as it would video level 18 with 16 set to put out the minimum amount of light, then the DI system may close the iris and raise that black floor up to try to get it to where it was previously. The reason being is that it isn't treating it as black.
I don't know what the JVC does there, but I think this could cause an issue where enabling the DI brings all of the negatives, but doesn't bring any positives. One way to check this would be to feed an all black image and switch between Manual and Auto 2. If the light on the screen doesn't change but the iris shuts down some, then I think a problem like this may be occuring.
Also, if there is light in the room that makes the screen visible when the projector is off this could throw off what a DI is trying to do somewhat also. For JVC's competitors this may not be much of a problem as long as there isn't a lot of other light, but JVC's on/off CR is high enough that it doesn't take much other light in the room to keep the system from actually getting the on/off CR that the JVCs are capable of. Then when a DI closes down an iris I think there could be some assumption in it that the projector is the only thing supplying light to the screen and can take advantage of how our eyes can adjust to different ranges. The other light can then throw this off and make it so that a projector that is providing more intra-image CR by use of a DI is actually providing less system intra-image CR due to the other room lighting.
I don't know if that is a problem with JVC's Auto 2 implementation and wouldn't be with the Planar implementation from what I know about it, but I think it would be with Sony's implementation and likely with JVC's Auto 1 (although I haven't checked it out enough).
Not sure if that made sense, but I'll try an example. It may or may not be even close to the conditions you have for testing.
I'll using something like I think Sony's system works. Let's assume that a projector is providing 10 ft-lamberts for white with 10k:1 on/off CR for about 0.001 ft-lamberts for black. I'll assume the room is adding 0.0005 ft-lamberts for black with the projector off, so system on/off CR is about 6700:1 system on/off CR.
Now I'll assume a dark image like a 5%/0% checkerboard on the 2nd edition of the Spears and Munsil disk. I'll assume the 5% blocks are about 1/700th as bright as white (due to gamma) and there is reasonable ANSI CR, so the intra-image there would be around 14:1 from the projector and about 9:1 from the screen (due to the extra room light).
That is without a DI enabled. Now if we enable a DI and this DI is one that for that image will dim the black 4x and adjust the gamma back 2x the 14:1 from the projector would get closer to 28:1. That is with the 5% rectangles about 1/1400th of the original white point, since they dimmed by 2x (from 4 divided by 2). Here the extra room light is going to hurt the image with the DI on more than with the DI off. With the DI off the room light is adding its 0.0005 to about 0.00025 instead of to 0.001. So that 28:1 from the projector becomes about 9:1 again.
Hopefully I did the math right there. If so, this is a case where just a little bit of room light meant that a DI that would increase the intra-image CR for that dark image from about 14:1 to 28:1 in a room without other lighting actually ended up with it staying about 9:1 off the screen. It would be no surprise if a person did not see any advantages from a DI in such a situation and only saw the negatives of a DI.
One thing these JVCs can do is show how much other light sources in a room matter. I think one good test is to show a full black image, then switch between blocking the projector and not. If there isn't much difference then the other room lighting is likely affecting the system on/off CR greatly. If there is a big visible difference then the room lighting likely isn't having much effect.
--Darin