I have been in electronics all my life but until now have managed to steer clear of video. So Im hoping one of you more knowledgeable guys can answer this question.
I have set up my pj (barco 801s) contrast and brightness levels using the test charts and I find the following.
When I watch video, black areas look really deep black and generally ok. but if I select a test chart and choose 0% white, which to my simple mind should be black, I get a darkish grey. similarly when there is no video signal the screen is a dark grey.
Now I assume this is something to do with black level clamping but why dont I get black out for 0% white signal. Or maybe its a trick of the eye just comparing the brightness levels of black in a picture to black on its own. dunno
Can any one explain it for me
thanks
Rod

It depends upon which black it is sending. If you are calibrated for PC levels (0-255) and the source is using video (BT.1361) levels (16-240).

This could be it. Also, black looks darker or lighter depending upon what is around it.

Dave

If its black around a light scene, then it will look somewhat gray due to light spill and especially if you have an air coupled projector. What color are the walls and floor?

He said 0% black (presumably a full-screen black field) was gray, so it's not halos, light spill, or wall/floor/ceiling reflection. Sounds to me like your brightness might be set a bit high. Brightness controls the low end, contrast controls the high end.

How exactly did you set it with the test chart?

BTW for most projectors, setting 0% IRE to complete blackout will crush dark areas, unless you do some gamma adjustment (boosting the low-IRE signals). I'm not a blackout fanatic so I prefer brightness levels that let me see shadow details, even if it means 0% IRE isn't 100% dark.

Actually I said 0% white , set with the test chart so that the second step from the last was just becoming visible as per the help text included with the charts, colorfacts charts by the way, both contrast and brightness are actually about midpoint on the adjustments too
thanks for the thoughts
rod

Oh, so it wasn't a full-screen black field? Then I was wrong, maybe it IS light spill or reflections. So black areas in movies look OK, but black areas in a test pattern (which is not entirely full-screen black) look gray?

No A full screen black looks grey but I have just been watching a film and looking at the blacks and a black in the picture really looks jet black whereas the border ( it wasnt full screen) looks grey BUT when a black was next to the border it seemed like it was the same colour as the border so maybe it is just a trick of the eye/mind
I tried altering the brightness while the film was running and it didnt make a visible difference to the surround ing grey but the picture did get darker.
maybe it is reflections, the room is a darkish red but the floor is lighter
I dont know.

Part of it is likely be a trick of the eye, but what is generating your full black field? I still contend that it may be at a higher level that the picture content.

Dave

You may be right but how do I tell ?

I'd say definitely a trick of the eye... if your blacks within the picture look black, but the black borders look grey, and then the same black moves to the black border and looks the same.. .what does that tell you?

In any case, try reading Darin's article here (http://www.hometheaterhifi.com/volume_13_2/feature-article-contrast-ratio-5-2006-part-3.html)

I found when I set my pj up using a computer for grey scale, that it wasn't the same when I switched to my video source (scaler). I experienced the same thing you are, a full screen black was grey. The fix for me was to turn on black enhance on the scaler. that pretty much fixed it. To get the best from it you need to set it up with each source you will be using, because each source is different. In my case my scaler enhances gamma. Get a setup disk like Avia to set up your video source correctly. What screen are you using?

My source is a pc and the screen is a white reflective gain of 1

g2's adjusted properly? Some people adjust g2 so that no light can be seen on the tube face on an all black field and some adjust it so that on screen looks black but technically the tubes are putting out a tiny amount.

Of course being a barco maybe yours just has those led's that you go by?

With an all black screen black should be black, and no light should be visible on screen, that is except in some movies that are just so dark I can't see crap and then I'll bump brightness enough to where I can see more black detail.

If you haven't adjusted g2's do so, get a service manual from curt palme's site.

Troy

I have adjusted G2s according to the book but that doesnt give you zero brightness on the tubes , I can do that of course but then the g2 leds (yes it is a barco) will be on and according to the service manual thats wrong cant win can I

I adjusted my 708s by he book with its led's and it does give no output with brightness around 50 on an all black screen.

If I bump brightness into the 55-60 range then I do start to get output. If you do the g2 with contrast a 50 and brightness at 50 and follow the led's then you should be fine.If there is still output Maybe something else is wrong. Leave g2 and just lower brightness until there is no output with an all black signal and tell us what brightness level output finally goes away.

The g2 procedure with led's stops working properly when tubes are high hour and emissions are low but I thought the symptom there was having too dark a picture, the opposite of what you seem to describle. I'm not all that familiar with barco's I've had a couple but really only spent any time with this current one, most of my experience is with marquee's and you just adjust g2 manually to where there is no output. It doesn't have LED's that think they know more than you do. :)

I can't imagine any possible way it would hurt to run g2 low even if the silly led's are on but I can't also see why that would be necessary. Is your source set to default output levels or have you cranked the gamma or brightness on it?

Troy