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post #1 of 11 Old 07-22-2015, 05:55 PM - Thread Starter
 
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Cool Our Darrin P in the news! Contrast Dept. News

HERE

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post #2 of 11 Old 07-23-2015, 09:08 AM
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I have been in both of his threads in the 3K+ section, but still fail to fully grasp the technical issue(s) debated, let's see if Chris can explain them to me at a more basic level.
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post #3 of 11 Old 07-23-2015, 10:44 AM
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Hi Donald,

I'm not sure what areas interest you other than audio and video, but I'll try a couple of analogies and see if that gets us any further.

I figure it may help to go back to how to properly test cause and effect.

In case a car analogy will help, let's say that a group testing race cars puts a 20 lb sail on top of a car and finds that the car slows down 5 seconds per lap. Would it be proper to assume that anytime 20 lbs is added to a race car it will slow down significantly?

For another analogy, lets say that somebody wanted to see how many alcoholic drinks it takes before people feel sick, so they send people out on a boat in high waves and count how many drinks it takes before people feel sick. If the average was 3, would it be correct to claim that 3 drinks on average will cause people to feel sick?

My position is that in both cases bad assumptions would have to be made to claim those things based on the testing. Proper testing would account for variables affecting the results. For instance, only change the one factor you think is causing the problem instead of changing multiple factors when any of them could cause the problem.

In this case the PISCR team shined lights at the screen to reduce CR. When ANSI CR went down to say 40:1 and sequential CR down to say 100:1 they saw unacceptable detail in mostly dark scenes and decided to claim that low ANSI CR like that would cause the same problem they saw. For a while I have been trying to get them to test just lowering ANSI CR (not sequential CR) so they can see with their own eyes what having low ANSI CR actually means versus what having both low ANSI CR and low sequential CR mean.

They made the mistake of extrapolating their results to cases they do not apply to. Shining lights at a front projection screen and testing for missing detail at a particular ANSI CR level does not tell you what happens in a white room with the same low ANSI CR. At least some of their members assumed that shining lights at the screen was good enough to figure out what happens in highly reflective rooms with the room lights low, but they assumed incorrectly.

Just because a system with 40:1/100:1 for those 2 CR test types has a problem with missing detail does not mean that a system with 40:1/500:1 for those 2 has the same problem. Proper testing would show that they overreached in their claims.

Thanks,
Darin

This is the AV Science Forum. Please don't be gullible and please do remember the saying, "Fool me once, shame on you. Fool me twice, shame on me."

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post #4 of 11 Old 07-23-2015, 02:23 PM
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Thanks for the succint summary of your argument, Darin.
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post #5 of 11 Old 07-23-2015, 04:19 PM
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One more thing Donald. I'll try to be succinct.

I think it is a shame if a customer asks whether putting in a dimmer switch for $500 which will leave them with 40:1/500:1 for ANSI and sequential CRs off the screen will be enough CR for watching movies and they are told that no, they need to spend $3000 to buy an expensive screen that will get them 80:1/120:1, but then don't need to put the dimmer switch in.

If they follow advice like that they will end up spending way more money to get inferior images for videos and movies IMO, but that is basically the direction PISCR pushes them (based on faulty assumptions and testing).

--Darin

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post #6 of 11 Old 08-01-2015, 03:54 PM - Thread Starter
 
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Hi Darin,


To your credit I hear through the grapevine that in the past decade you have previously touched on a couple of the concepts inherent in IMAX NEW Proposed Patent for Wavelength dependent active Aperture.HERE.


Color dependent aperture stop
Optical systems are provided that include illumination sources, micro-mirror array optical modulators, and an optical element. The micro-mirror array optical modulators can selectively modulate light beams, redirect light by diffraction and reflection, and provide an output modulated light beam that exhibits a diffraction handedness dependent on the spectral bandwidth of the light incident thereupon. The optical element has a color dependent aperture that defines portions of output modulated light beams that are transmitted and remaining portions that are blocked. An efficiency and contrast of each the output modulated light beams acquired by the optical element can be independently determined by a narrow spectral bandwidth of each of the light beams, the spectral characteristics of the color dependent aperture, and the diffraction handedness of the micro-mirror array optical modulators for the associated spectral bandwidth.


Care to comment on it?

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post #7 of 11 Old 08-01-2015, 05:38 PM
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http://dci-forum.com/index.php?topic=384.0 correct link, Peter posted the link to the '=post' window, and that results in a window that we can't edit just any post.
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post #8 of 11 Old 08-08-2015, 10:00 PM
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Quote:
Originally Posted by CINERAMAX View Post
To your credit I hear through the grapevine that in the past decade you have previously touched on a couple of the concepts inherent in IMAX NEW Proposed Patent for Wavelength dependent active Aperture.HERE.
Thanks for the pointer to that Peter. I haven't read through all of it, but am fascinated by some I have read.

Years ago I modified an Optoma H79 in a way where I put in basically 4 irises (or openings for light to pass). Two in the lens side-by-side where one was red and one was clear, then corresponding irises side-by-side before the lens. One reason for this was the red deficiency in UHP lamps where I could get close to D65 without the contrast ratio reduction of reducing the gains for blue and green and could actually improve the blue and green sequential CRs with tighter irises than I would have needed if all irises passed all wavelengths. Also, my experience and understanding is that red is harder to see in very dark images and so doesn't need as much sequential CR, but this mentions blue requiring less CR than green and red. I understand focus for blue being less important, but was surprised about this comment for CR. Maybe I missed something in their reasoning.

In my case I couldn't make those irises dynamic since I didn't control the signal or have a way to do that.

I've tried to explain some advantages of matching up irises before a DLP chip and in the lens previously using dime sized openings and quarter sized openings as examples, but I think this does a better job of explaining this than I did, where it has:
Quote:
First, the working f-number for light exiting the first system can be matched to the working f-number for light entering the second system, which can help allow an axial bundle of light to be coupled efficiently. Efficient coupling may relate to cost and light throughput. If a first system has a small f-number and a second system has a larger f-number, then some light may be lost by joining these together. If a first system has a large f-number and the second system has a lower f-number, then no, or substantially no, light is lost but the second system is “too expensive” because it is overdesigned to work at a larger aperture size. Thus, one way is to match the two systems.
I found it really interesting that going to 4K DLP chips was causing them issues due to defraction and different color wavelengths.

One thing I thought we might see in commercial theaters like IMAX by now was dynamic irises. I filed some preliminary patent things years ago related to dynamic irises and recall including that for commercial theaters showing the same content over and over the iris positions and modified source levels could be pre-encoded. They wouldn't have to deal with the same issues as consumer projectors of not knowing what the next frames are like. At the least they could delay the content while figuring out the best iris position, but having an expert pre-encode them would seem better to me. I understand IMAX already does some of their own processing ahead of time, so this extra feature seems like a good fit.

I realize commercial theaters have limited black floors not including the projector, but even so I think that dynamic systems could have provided some improvement even before now.

--Darin

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post #9 of 11 Old 08-10-2015, 09:26 PM
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In several old threads where

Quote:
Originally Posted by darinp2 View Post
I found it really interesting that going to 4K DLP chips was causing them issues due to defraction and different color wavelengths.
In several older threads where people expressed the hope that the new 4k chips would have higher CR, I remarked that it would be an uphill battle because for the same DMD size, the ratio of length of mirror edges (where diffraction occurs) to mirror area is higher.

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post #10 of 11 Old 08-10-2015, 10:49 PM
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Quote:
Originally Posted by noah katz View Post
In several older threads where people expressed the hope that the new 4k chips would have higher CR, I remarked that it would be an uphill battle because for the same DMD size, the ratio of length of mirror edges (where diffraction occurs) to mirror area is higher.
I wonder if this is something else since they mention it affecting the different wavelengths different amounts.

It has:
Quote:
In support of the development of laser projectors, transmission experiments were performed using red, green, and blue lasers. Unacceptable efficiency losses were observed with various combinations of laser wavelengths and 4K DMD devices. These losses may be due to increased diffraction from the finer pitch of the DC4K chip. Diffraction occurs when propagating waves (e.g. light waves) encounter an obstacle and its behavior is modified. This can happen, for example, when the size of the obstacle is similar to the wavelength of the wave and when the obstacle includes multiple, closely-spaced openings. This can also result in a complex spreading of the distribution of light not predicted from geometrical optics.
Maybe it is just the amount of mirror edge length per square inch, but they seem to think it is more than that.

--Darin

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post #11 of 11 Old 08-12-2015, 12:38 PM
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Ah yes; besides random diffraction from edges, rows of edges could can act as a diffraction grating.

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