AVS Contrast Thread - Now with Dynamic Contrast Results! - Page 3

It in itself doesn't increase contrast ratio. But it's gain allows you to utilze the high contrast iris settings in today's dlp's.

If on high contrast iris mode you are only getting 4.5ftl, that would be unacceptable to most. Sure the black level would be really low, but could you put up with the white level? If you can, then great, but many would find that to be too dim.

At that point you have 4 choices:

1)4,500:1 on/off, narrow iris, .001 black, thus only 4.5ftl. 1.0 gain screen.
2)2,700:1 on/off, med iris, .003 black, thus 8.1ftl. 1.0 gain screen.
3)4,500:1 on/off, narrow iris, .003 black level, thus 13.5ftl. 1.0 gain screen, but a significantly smaller one.
4)4,500:1 on/off, narrow iris, .003 black, thus 13.5ftl. 3.0 gain screen.

So as you can see, with choice 4, with the high gain screen, it's the only way to get maximum contrast, brightness, and screen size all at the same time.

I know you don't want to raise black level, but unless the pj can do 8,000-12,000:1, you can't have .001 black level and sufficient brightness

#4 is same as #1 with a 3xgain still same cr but 3x lumen at the price of 3x worse black level. I just don't see any cr advantage.

What do you mean #2 is incorrect? 2,700x.003=8.1

If you can live with #1, then a high gain screen is not for you. You honestly could live with 4.5ftl?

I am really comparing #2 and with #4, showing that you can actually get more brightness and contrast with a high gain screen. I didn't think #1 would appeal to anyone.

Multiplying CR times BL gives you WL. You need screen size to get FtL!

That's right. Don't know what I was thinking. Let me fix it.

CR times the ft-l gives ft-l as cr is unitless. Ft-l times screen area gives lumen.

It is higher CR at certain ft-lamberts and screen size limits (you don't want to go any dimmer than x ft-lamberts or any smaller than y" wide). If you don't care how many ft-lamberts you get for white and are willing to go as low as the projector and screen gives you in its most closed iris mode, then you are already getting the most CR it is capable of. But with certain screen sizes and 1.0 or 1.3 gain the highest CR mode would be considered unusable by many people, because the ft-lamberts for white would be too low. Put another way, it allows some people to use the high CR mode and be happy, instead of preferring the lower CR mode because it is the only one that gets their whites bright enough.

The above is of course for projectors that have multiple user choices for CR, where the higher CR modes are dimmer for white (like DLPs with 2 adjustable irises inside).

--Darin

Okay, I think I got this right.

If on high contrast iris mode you are only getting 5.4ftl, that would be unacceptable to most. Sure the black level would be really low, but could you put up with the white level? If you can, then great, but many would find that to be too dim.

At that point you have 4 choices:

1)4,500:1 on/off, narrow iris, .0012 black, 5.4ftl. 1.0 gain screen, 92" wide, 180 lumens.
2)1,300:1 on/off, wide iris, .0092 black, 12ftl. 1.0 gain screen, 92" wide, 400 lumens.
3)4,500:1 on/off, narrow iris, .0027 black, 12ftl. 1.0 gain screen, 62" wide, 180 lumens
4)4,500:1 on/off, narrow iris, .0027 black, 12ftl. 2.3 gain screen, 92" wide, 180x2.3=414 lumens.

So as you can see, with choice 4, with the high gain screen, it's the only way to get maximum contrast, brightness, and screen size all at the same time.

I know you don't want to raise black level, but unless the pj can do 8,000-12,000:1, you can't have .001 black level and sufficient brightness

Mark
thanks for the update, good stuff

Test equipment suite and test methodology and procedure are critical items to get comparable numbers in any testing program. I have not been able to find this information in this thread, although it should feature prominently near the top of the page, IMHO.

Where are these items documented?

Yes, I read that. What is the "probe sensor" ?

The context is that test patterns .zip file that you referred to in your previous post, that explains the test method for measuring contrast. What make and model of light meter is specified for this measurement? I imagine that could have a large effect on the numbers you measure.

Why? There is no make or model of any measurement devices specified for the on/off or ANSI CR benchmarks?

Not entirely true, one needs to be sure the light meter being used can accurately measure the black levels of the projector. Many light meters give readings at low light levels, but accuracy is the big issue.

I didn't ask what light meter was specified in any ANSI spec. I am only interested in finding out how the data was taken in the contrast tests referenced above. There must be about 500 different light meters one could use for that, and I am rather sure not all of those instruments are going to return the same numbers. This is supposed to be AV Science Forum. If I were discussing an experiment with a scientist and I asked him what instrument he used in his measurements, he would tell me.

Not if you ask 'What is the "probe sensor" '? Anyway good luck!

As a practical matter has any one done a Histogram which gives the probability of any scene in any film having a certain range of APL.

I know some films are dark and some films are bright but what does the distribution look like?

***
Subjective ... complicated ... so adjust to you taste...

I agree and would add there is not even a clear way to calculate and select even the screen size. Its just too complicated as there is no one good or simple answer.
Below are the many Sony VW50 brightness outputs according to measurements from the SMPTE brightness thread.

Note: this is the first and last time that I'll expect to read this thread as it just too complicated. It unintentionally reinforces that dynamic iris is an unpredictable band-aid solution.
***

Sony VPL-VW50 Screen Calculations for 12fl Brightness & 1920*1080 Best Viewing Distance

Measurements are from WSR magazine issue 115. The calculations are being provided because the new Sony VPL-VW40 is supposed be similar to this model.
We are taking the long route here with four screen sizes per lamp setting, as these are the boundaries from which the auto iris adjusts itself, depending upon the particular frames signals content. In other words the Auto iris varies from best contrast to best brightness while also introducing compression at the top. Take you pick of one or the other, but never the two simultaneously.

The review does not take into account the 50% reduction in brightness due to bulb aging for selecting a screen size. We do here

Best Contrast, Worst Brightness (Auto Iris mode = off)
-------------------------------------
Sony VPL-VW50, low lamp, minimum lens aperture, 1.0 screen gain
sqrt(14*234*1.0) = 57 inches maximum diagonal screen size, 5.7ft best THX viewing distance

Sony VPL-VW50, low lamp, minimum lens aperture, 2.5 screen gain
sqrt(14*234*2.5) = 90 inches maximum diagonal screen size, 9.0ft best THX viewing distance

Sony VPL-VW50, high lamp, minimum lens aperture, 1.0 screen gain
sqrt(14*361*1.0) = 71 inches maximum diagonal screen size, 7.1ft best THX viewing distance

Sony VPL-VW50, high lamp, minimum lens aperture, 2.5 screen gain
sqrt(14*361*2.5) = 112 inches maximum diagonal screen size, 11.2ft best THX viewing distance

Worst Contrast, Best Brightness (Auto Iris mode = off)
--------------------------------------
Sony VPL-VW50, low lamp, maximum lens aperture, 1.0 screen gain
sqrt(14*432*1.0) = 78 inches maximum diagonal screen size, 7.8ft best THX viewing distance

Sony VPL-VW50, low lamp, maximum lens aperture, 2.5 screen gain
sqrt(14*432*2.5) = 123 inches maximum diagonal screen size , 12.3ft best THX viewing distance

Sony VPL-VW50, high lamp, maximum lens aperture, 1.0 screen gain
sqrt(14*652*1.0) = 96 inches maximum diagonal screen size, 9.6ft best THX viewing distance

Sony VPL-VW50, high lamp, maximum lens aperture, 2.5 screen gain
sqrt(14*652*2.5) = 151 inches maximum diagonal screen size, 15.1ft best THX viewing distance

Notes
1) reviewers state the picture quality is superior with the auto iris engaged
2) auto/dynamic iris mode makes exact screen selection painful as the size falls somewhere between the highest contrast or highest brightness sizes. As a rule, higher contrast equates to better picture quality. Each owner must select some screen size. Or as an alternative, choose a projector which does not require a dynamic iris to achieve optimal picture

Guys, I have some interesting results to post.

I have to do one more measurement with Ken to make sure our results are in fact in line with my first measurement.

Cliff

Mark,

Ken and I have finished measuring my complete on/off for the stack using the "into the lens" method with his Minolta meter.

My results are interesting as in I have discovered that I have to replace my red tubes in both of my G90's as they have too high of hours and are causing raster glow because of this. If I replace my red tubes, my numbers are certain to go much higher.

With this being said, I am still COMPLETELY happy and extatic with the results!!!!!!!

Screen size - 10ft wide SMX 1:85

Foot lamberts at 100IRE off of screen:

10 foot lamberts

G90 stack measured ANSI contrast (using checkerboard pattern from DVE) measured off of the screen:

80 to 1

Here are my on/off contrast numbers. Ken and I measured directly into the lens on both 0 and 100 IRE (Zero being VIDEO BLACK and 100 being VIDEO WHITE using DVE test patterns).

Projector one Zero IRE (Video Black) measurements:

Red tube - .188 FL

Green tube - .002 FL

Blue tube - .001 FL

Projector two Zero IRE (Video Black) measurements:

Red Tube - .033 FL

Green Tube - .004 FL

Blue Tube - .001 FL

All numbers added up then divided by 6:

.038 FL

Projector one 100 IRE (Video White) measurements:

Red Tube - 3680 FL

Green Tube - 14,470 FL

Blue Tube - 9969 FL

Projector two 100 IRE (Video White) measurements:

Red Tube - 3412 FL

Green Tube - 13,980 FL

Blue Tube - 1209 FL

All numbers added up and divided by 6:

7786 FL

7786 FL Divided by .038 FL Full ON/OFF Contrast for a G90 STACK:

204,894 to 1

10ft wide 1:85 SMX at 10 Foot Lamberts produces 80 to one ANSI Contrast and 204,894 to one Full ON/OFF Contrast. Not bad huh?

If the ANSI numbers seem really low to you, they are not. The same light meter (minolta) from a 3 chip DLP will roughly measure over 2.5 the ANSI of my stack in the same configuration.

Ken will be bringing over the Joe Kane Samsung to which I will measure ANSI on my screen while it is here hopefully to give you an idea.

Much thanks go to Darin for helping us to come to the proper method of doing this.

Cliff

Thanks for the info, very interesting. If you get the chance, would you consider measuring all the static contrast patterns in the first post (I think) of this thread? It would be very interesting to see how a CRT performs at various APLs.

Interesting numbers Cliff. If you get a chance could you try a subjective test with Finding Nemo. Basically, measure approximately how long it takes before you can see the edge of the screen when the image blacks out in the Abyss scene.

Do you think your dealer friend will be bringing an RS20 over for comparison when they come out?

Approximately how much does a red retube for the G90 cost these days? Is there anything you could do in the meantime like lower your offset for the red tubes? Looks like you are way over a million to 1 just considering blue and green.

Also, if the Minolta LS100 that Ken uses is like the LS110 I have used then it may not be able to measure ANSI CRs over about 200:1 unless a dark light pipe is put on the end of it. I made a pipe out of some somewhat stiff paper type board that I covered with black velvet and then rolled up. I think I had to go to about 18" long for the pipe to get it to work well. If the room isn't taken into account then I'm guessing the Samsung could do 500:1 ANSI CR or more.

--Darin