Grayhawk, HC DaMat, or KBKs paint?

Kelliot.

You never took me up on a factory tour.

Bring your projector and you can try one.

By the way...The gray is much darker on the

Grayhawk than the gray scale card that you mentioned.

How about after CES?

Regards,

Don

Don,

I am negligent in that respect but still intend to take you up on it. Its just far less time consuming to do things at home. If the Grayhawk is effectively grayer I should be much happier with it. I base my statements on the published and anecdotal data.


KFung,

The only way that measured gain can differ between the white and dark ends of the scale at these light intensities is if ambient is playing a role. I think that Noah Katz and some other posters have explained this. Its also been pointed out that dark or black frames present the toughest case.





[This message has been edited by kelliot (edited 01-04-2001).]

kelliot,


If you can point me to that thread, I would love to read it over. I don't remember it very well (I might have missed it).


However, I don't think their discussion quite covers this situation. Noah was probably talking about comparing the contrast ratios of regular and gray screens. Don's test was not comparing regular and gray screens though, it was comparing a small sample of a regular screen and a gray screen. The situation is a little different, instead of measuring values off a full size regular screen, the values now come off a very small sample. If you have time please read my post in this thread http://www.avsforum.com/ubb/Forum9/HTML/000583-3.html after Don posted his results. It explains why I think that Don's use of a small sample instead of a full size regular screen makes all the difference. The short of it is that with a small sample the ambient light would be the same for both the gray screen and small sample measurements.


I'll attempt to elaborate here:

Mr. Wiggles' post in the same thread shows how a gray screen can increase ANSI contrast ratios. This is because there is less ambient light bouncing around the room, which makes sense right? Less ambient light to pollute the black level. The same decrease in ambient can be achieved if you make everything in the room darker instead of using a gray screen, this likewise decreases ambient light. In fact, if you made your room very light absorbant you could increase your ANSI contrast without a gray screen. I believe the consensus that Noah's thread probably reached was that, while ANSI contrast is enhanced by a gray screen, actual contrast in the abscence of ambient light is not. Is that right? The increase in ANSI contrast comes from the difference in ambient light from a regular screen and a gray screen.


However, if you finagled it so that the regular and gray screen both had the same amount of ambient light when you tested them, you would find that their ANSI contrasts would be the same. The is what Don did when he used a small sample in his test. What cannot be explained by ambient light is why the ANSI contrast ratio was different for the small sample and the GrayHawk screen when the ambient level of light was the same for both measurements.


Not the best explanation, I know.


Regards,


Kam Fung

The crux of the problem is the uncertainty in measurement of very low light levels. The balck level can easily be off by 30% if a strong white is present as with an ANSI contrast measurement.


A full on/full off measurement is more straightforward because projector related ambient is minimized. This is also the case when most of us notice that the black screen is closer to gray tahn black. It is very difficult to get different contrast ratios with a full on/full off measurement because the balck and white intensities don't mix.

However, the ANSI contrast has an ambient term that is quadratic in the gain of the screen. Hence very modest gray levels (matte gain=.8) can produce excellent reductions in black level. (.64) with an aparent improvement in contrast of (1/.8) or 125%. This only effects the screen-based ambient and not the direct contrast term(projector) or other ambient terms(lights,windows). It also changes with environment (like black walls) so its tough to quantify in a standard way.


I myself prefer a gain of .65-.7 at >500 lumens/m^2.




[This message has been edited by kelliot (edited 01-05-2001).]