Looking for better blacks during dark scenes (JVC HD350). - AVS Forum
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post #1 of 22 Old 02-01-2012, 05:01 PM - Thread Starter
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Hi,

I'm using a hd350, around 5m from a 120" grey screen in a light controlled room. 700 hrs on the lamp. High power mode and iris level 3 (max). PJ has been set up with the AVS HD test disc, All the bars that should flash on the b&w tests do flash.

The problem I have is that during very dark scenes in a movie, after about 2 seconds, the screen masking becomes visible. After around 5 seconds, the screen looks like a cheap TFT monitor doing its best to produce black.

I've tried reducing the iris (which helps) , but the picture loses its punch, and just becomes darker.

There's no problem (to my eyes) with black levels when there's a bright scene involved, or say the green calibration grid on the test menu, it's scenes where there's almost no light, like looking into space and seeing stars.

I was going to add black velvet to the room, but I don't think it's the room that's the problem. When I activate the 'hide' function on the projector, the PJ doesn't put out enough light to illuminate the room significantly (the black surround kills any reflections), but there's enough light hitting the screen to make it easily visible.

I used my Wavetek Meterman LM631 Digital Light Meter to take some measurements.

Background light in the room with the PJ off. 0.00 Lux
With the PJ on, picture hidden, at the screen, 0.00Lux (but I can see light, and waving my hand infront of the screen casts a shadow)
With the PJ on, picture hidden, 1m from the lens facing the PJ, 0.13Lux
With the PJ on, white test pattern, 1m from the lens facing the PJ, 2000Lux

That's a ratio of 15.3k, just over half of the supposed 30k:1 advertised ratio.

My questions:

1. Do any other HD350 owners on here see the screen when the picture is hidden? Assuming you can't see it when the PJ is off. If so, how long does it take before your eyes adjust to the 'hidden' screen (the screen door on my PJ stays open)?

2. Is the light level I measured 1m from the lens in hide mode normal?

I assume it's my eyes iris that are opening up when the picture darkens, causing the problem. Any tricks out there to stop this, like maybe lighting the people somehow without lighting the screen?

It could be that my PJ is operating correctly, but without another JVC to compare it to I have no reference. I'd be interested to hear of other owners answers to question 1 above, and perhaps 2 if they have a light meter.

Thanks.
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post #2 of 22 Old 02-01-2012, 06:42 PM
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Check your hdmi settings. Set it to auto, or if that doesnt work, set it to opposite it's current setting. (enhanced/standard).
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post #3 of 22 Old 02-01-2012, 06:46 PM
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And also, yes, you will still still see a shadow cast. Black isnt perfectly black. But it is close, and should look WAY better than a TFT monitor.
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post #4 of 22 Old 02-01-2012, 07:56 PM
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Quote:
Originally Posted by fiscoking View Post

That's a ratio of 15.3k, just over half of the supposed 30k:1 advertised ratio.

To get the 30k:1, my understanding is you'll have to run in low lamp, long throw, with the iris completely closed down.

Quote:


1. Do any other HD350 owners on here see the screen when the picture is hidden? Assuming you can't see it when the PJ is off. If so, how long does it take before your eyes adjust to the 'hidden' screen (the screen door on my PJ stays open)?

I don't believe there are any projectors that can pass the "hand puppet test"*. Going by the math from some some data posted from a NASA study a while back, I figured you'd need on the order of 10 million:1 sequential contrast ratio have black be actually invisible.

*Now there are some projectors, specifically LED DLPs which actually turn off the LEDs (light source) for full black frames, so these can actually "produce" true black for blackouts. Of course the merits/usefulness of this technique is rather hotly debated here.

Quote:


I assume it's my eyes iris that are opening up when the picture darkens, causing the problem. Any tricks out there to stop this, like maybe lighting the people somehow without lighting the screen?

Yup, it's exactly that, our eyes can adjust to an incredible range of brightness, on the order of at least 100 million or 1 billion to one (possibly even more), but cannot perceive nearly that simultaneously, so if there's even a bit of light it causes the eyes to adjust to that brighter light and thus the black appears darker.

About the only thing I know of that can be done is bias lighting, you place lights in the room, around, or behind the screen so that when the projector fades out, your eyes don't dilate because of the light around the screen.

Of course this has the problem of lighting up the screen as well, largely defeating the purpose.

See what an anamorphoscopic lens can do,
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post #5 of 22 Old 02-02-2012, 01:23 AM
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Bias light improves perceived black level.

If your screen stands away from the wall behind it by a good several inches, you can install a bias light to create a halo around the screen. This bias light prevents your eye from opening too much. In a totally dark room, your eye normally opens wide and screen black appears grey.
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post #6 of 22 Old 02-02-2012, 01:59 AM
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The eye is a light sensor and definitely not a black sensor.

All of us love astounding blacks, but keep in mind that the eye functions entirely by light. Absence of light means total disfunction and you are at the mercy of any hungry animal approaching to find something to eat.

One frustration many people have discovered is that the more you successfully black out a room, the more black level appears grey. Instead of covering the front wall with black velvet, you might try leaving the wall beige or white. Install a 15 watt lamp towards the back of the room, and the wall lights up a bit and you eye shuts down just enough to perceive screen black as black.

Think of your projector as a movie machine rather than a blackness generator. Is your projector any good at presenting a movie? Are daylight scenes like daylight? If your projector functions only as a blackness generator, find another one and get happy.
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post #7 of 22 Old 02-02-2012, 07:32 AM - Thread Starter
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Thank you for your replies.

Light biasing is something I could try (I'd not heard of this before now). Aiming for better projector contrast might be worth a go too, but it will be expensive.

I suppose dropping the lamp light level, closing the iris, velveting the room and moving to a white screen (instead of grey) could help. This should produce the same screen brightness (as the gain of the screen will be higher), but there will be less reflections from the room if it's darker, so I'll benefit from increased projector native contrast, while losing no screen brightness.

I've got some 1.0 gain screen material from Harkness Screens. I'll fix it to my grey screen tonight and play with the PJ settings to see if a white screen will look darker with the iris and lamp in low mode.
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post #8 of 22 Old 02-02-2012, 09:13 AM
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If your setup supports it (projector location) a High Power screen would probably help, it would "recover" the light you lose going from iris wide open to fully closed.

And I should mention, I guess it's not technically right that the lamp mode should make a difference, theoretically lamp power shouldn't affect contrast, just iris and zoom/throw.

See what an anamorphoscopic lens can do,
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post #9 of 22 Old 02-02-2012, 11:37 AM
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Quote:
Originally Posted by emf View Post

Instead of covering the front wall with black velvet, you might try leaving the wall beige or white. Install a 15 watt lamp towards the back of the room, and the wall lights up a bit and you eye shuts down just enough to perceive screen black as black.

A light at the back of the room will be counterproductive, as it will light up the screen.

I think the best effect with the least light added to the room would be some tiny bright LED's at the front.

Noah
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post #10 of 22 Old 02-03-2012, 04:48 AM
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Here's something I posted on U-Tube a while back...

My HD350... projecting onto 84" screen from about 4 meters back.

Approx 2,400 hrs on the lamp at this point.

Aperture was set to '2'. Normal lamp power (not high).

Perfectly bright enough in my room, with superb deep inky blacks.

This video was done with an iPhone4. The bright parts of the picture are actually brighter than this video portrays.

Anyway, it's here:-

http://www.youtube.com/watch?v=lpXQUDwQCho

Darren
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post #11 of 22 Old 02-03-2012, 07:25 AM - Thread Starter
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That youtube video is impressive.

I guess after a year of watching movies on my JVC, I'm beginning to notice more of the abberations in my cinema. A bit like living in a house for years and one day noticing that smudge on the ceiling. It's always been there, you simply never noticed it until now.

I tried the 1.0 gain screen material on my grey screen and in the dark (PJ off), no difference. With the PJ on, pic hidden, the white material stood out a bit, but not in a big way. With the in-built green calibration grid on, there was no difference at all. The blacks in between the green lines was just as black on the white material as the grey. With colour patterns, the blacks were washed out on the white, but that just demonstrates that it's my room that needs some more treatment (suede \\ velvet) as the colour patterns did light up the room, but the green grid didn't (black paint isn't all that black under light).

The 1.0 gain material from Harkness was impressive for colours. Way more image 'pop' (put the grey screen to shame on that level), but the blacks suffered during light scenes (compared to the grey screen). Now I understand why people want a dark room to keep the blacks in check.

Based on the above, I'm going to add more black material to the ceiling and walls, and perhaps the rear of the room, and try some bias lighting behind a 1.0 gain screen.

A bit off topic, here is a picture I've taken with some black materials. I wanted to test them before ordering a big roll.

The projector stand is painted in 'Dulux trade, flat matt black' (their darkest black). High power flash to highlight which is best....the winner.....Devore. At half the price, EPRA's Tripple black comes a very close second, but the picture does it a dis-service. It looks a lot darker than in the picture when you're not blasting it with light. In fact, under normal diffused light, it's difficult to tell the difference between the two. The tripple is not as acousticly transparent as the devore though. It got a backing on it that reduces air flow, and reduces stretch. The Jersey is more acoustically transparent than the Devore, and it's stretchy too, so a good contender for a speaker covering.

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post #12 of 22 Old 02-03-2012, 12:45 PM
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Quote:
Originally Posted by avzektor View Post

Here's something I posted on U-Tube a while back...

My HD350... projecting onto 84" screen from about 4 meters back.

sorry, but viewing pj's with a phone is no better than auditioning speakers over the phone

Noah
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post #13 of 22 Old 02-06-2012, 09:56 PM
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@Noah Katz

You are right. A light in the back of the room throws light at the screen and that's definity not desireable. Fiscoking mentioned that his screen was 120" GREY screen.

If the wall behind the screen is white or beige, it lights up all around the screen very well and his screen not so well. This is the main advantage offered by a GREY screen: reduced sensitive to room light.

A WHITE screen picks up any light in the room, in which case best location for a bias light is at the front, preferably behind the screen plane.
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post #14 of 22 Old 02-07-2012, 10:41 AM
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Quote:
Originally Posted by emf View Post

This is the main advantage offered by a GREY screen: reduced sensitive to room light.

There is an improvement in black level, but at the expense of lower white level; CR is not improved.

Noah
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post #15 of 22 Old 02-09-2012, 08:03 AM
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If you want a screen that is good with ambient light, then a gray screen with gain is what you want. These screens have a gray base that drops the gain below 1, but then the optical coatings that are added to the screen give them a positive gain.

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post #16 of 22 Old 02-09-2012, 12:48 PM
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Quote:
Originally Posted by noah katz View Post

sorry, but viewing pj's with a phone is no better than auditioning speakers over the phone

Absolutely agree. In no way does the video give any true representation of image quality. However, it does give a good idea of how dark the black level is compared to a Samsung panel on its lowest possible back light setting.

The intention of the video was to give people an idea of just how deep the black level can be with a decent projector compared to an average LCD TV. Especially for those people that have no idea on how good a quality projector can be.

Darren
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post #17 of 22 Old 02-09-2012, 01:04 PM
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Quote:
Originally Posted by noah katz View Post

There is an improvement in black level, but at the expense of lower white level; CR is not improved.

Depends on room setup and on uneven reflections hitting the screen, some screens preserve Ansi contrast. Native On/Off will generally not be affected however, but I'm sure there are some exceptions even to this such as light pollution entering the projector itself or the lens path area.

@OP
Getting the best calibration possible, best gamma curve, luminance, and color will help the richness of perceived black levels and shadow detail.
Even a cheap eye-one LT can give you really accurate luminance and a pretty good read on gamma, even if the gray-scale color readings are off a bit.



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post #18 of 22 Old 02-09-2012, 08:38 PM
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Quote:
Originally Posted by coderguy View Post

Depends on room setup and on uneven reflections hitting the screen, some screens preserve Ansi contrast. Native On/Off will generally not be affected however...

I was commenting only on the gray vs. white aspect, and maintain that neither ANSI nor on/off are affected by it.

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post #19 of 22 Old 02-10-2012, 07:10 AM
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The thread was referring to high-gain gray screens...
Since these gray screens have specific gain properties, they are able to redirect and reject some of the light pollution to improve ANSI contrast much in the same way that a regular retro-reflective gain screen can. Although I've never personally attempted to measure it, but altering light pollution would increase ANSI.



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post #20 of 22 Old 02-10-2012, 10:11 AM
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Quote:
Originally Posted by coderguy View Post

The thread was referring to high-gain gray screens...

That thread is not relevant to my point about grey vs. white, which I belabor because it's frequently misunderstood.

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post #21 of 22 Old 02-11-2012, 04:53 PM
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Fiscoking insists his JVC seems to not project black enough black.

Our site member fiscoking has JVC HD350, a grey 120" screen, and a light-controlled room. He asks what to do.

In one room, I have a Sharp flatpanel TV. At the store, the black appeared very black. But in my house, the TV black appears kind of crappy. When sunlight streams into the room, the TV seems to regain its glorious blacks. Watching programs at night, the TV returns to its crappy black.

Turning on a lamp did the trick. Ambient light in the room shuts down my eyes just enough to reduce light coming to my retina.

I tried another variation. By placing a small lamp behind the TV, blacks appeared magnificent. I quit it when I felt the TV image presented the impression of a Kodachrome transparency. TV programs should look like TV.

@Noah Katz - Your suggestion to use bright LEDs at the front should work. LEDs would throw light into his eyes, and his eyes would adapt by shutting down just a bit and blacks will appear blacker.

At Fry's Electronics I purchased a string of white LEDs specifically for the purpose of lighting from the front of the TV, preferably bouncing off the ivory wall. The LEDs were too bright. In addition, there was the problem of mounting LEDs and the problem of electrical connection and switching them on/off.

Since he already has a GREY screen and a white wall (houses in this country come with white interior walls), fiscoking might remove black paper, black cloth, or black velvet from the FRONT wall. You might guess he already has a small lamp; and it will light up the wall just enough to make projector black appear blacker.

Some people on this site are discussing lasers for projectors. Both lasers and LEDs can modulate light down to total turn off. A bias light gets the job done for the moment.
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post #22 of 22 Old 02-11-2012, 06:26 PM
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Quote:
Originally Posted by emf View Post

The LEDs were too bright.
...
Both lasers and LEDs can modulate light down to total turn off.

So just use a dimmer, or wire them in series, series/parallel etc.

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