AVS Contrast Project v2.0 (updated 1/26/07) - AVS Forum
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Digital Hi-End Projectors - $3,000+ USD MSRP > AVS Contrast Project v2.0 (updated 1/26/07)
Mark Petersen's Avatar Mark Petersen 09:42 PM 01-04-2007

Background:


Contrast has long been considered a key display specification, but in todays environment with projectors having dynamic irises (DI), fixed irises, high-ANSI but average on/off CR and high on/off CR, but average ANSI contrast it's clear that a better description of contrast is needed. The traditional metrics used in the industry are sequential (e.g. Full White / Full Black) contrast and the ANSI checkerboard contrast test pattern. Sequential contrast is a useful metric for gauging the maximum contrast achievable in the darkest of scenes as luminance approaches 0 while the ANSI checkerboard contains 50% peak white luminance which is much brighter than a typical movie or video scene. One drawback to using only these two tools for gauging contrast is that both of these test patterns describe only the fairly extreme bright and dark ranges that would occur in a typical movie scene. Film based content is a dark media with ~20% average picture level (APL) so it's clear tht most scenes fall in between the traditional measures of sequential and ANSI CR. We will also show that trying to apply traditional sequential contrast is no longer an applicable figure of merit for gauging the static contrast for dynamic iris projectors at 0 luminance and we will provide an alternative definition that describes both non-DI and DI equipped projectors alike.

What this project attempts to do is gain a better understanding of projector performance in several interesting ways. One is through the definition of a new suite of contrast test patterns (The "Phelps/Petersen Contrast Test Patterns"), Another is through mathematical modeling methods implemented by Erik Garci and another is by relying on individual forum members to supply data on their own projectors which can be maintained and displayed in a database as an ongoing effort.

A word on Contrast

In the following discussion it's best to think of contrast as a function of luminance, the higher the luminance the lower the contrast. The measured (and in some cases modeled and predicted) contrast functions for several projectors can be found in the contrast chart and each point along the luminance curve gives a person a rough feel for the contrast with a specific amount of luminance. Rather than complicate this project by using pixels with grey luminance which in turn can deviate based on projector gamma, this project defines test patterns with pixels using only full white and full black. Varying degrees of luminance are achieved by using more white pixels organized into boxes of different sizes and numbers. Since contrast is always a relationship of white to black, it's useful to think of these test patterns as representing "static" or "simultaneous" contrast because like traditional ANSI test patterns, the contrast in these test patterns can be can be seen and measured at one time and even with a a dynamic iris projector the measured contrast is fixed (ie static)..

The Phelps/Petersen Contrast Test Patterns

These test patterns will soon be available for public download and they contain multiple test patterns that allow consistent measurements of contrast with varying degrees of full white luminance. These test patterns range in luminance from 0.1% to 100% (full white) and also include the equivalents of ANSI CR and Full On/Full Off patterns. These test patterns were designed for constant probe position so that all a person needs to do is set up instrumentation and then go through the test patterns one by one and record the white and black readings. Once the test patterns have been finalized a link or e-mail address ffor download will be provided here.

Mathematically modeled contrast

In addition to directly measuring contrast as a function of luminance, Erik Garci has created the contrast calculator which allows us to extrapolate contrast values from ANSI and On/OFF CR. In some of the curves below are several diagrams comparing theoretical performance of projector types as well as a comparison between actual and predicted values. Here is a link to the contrast calculator for those who would like to use it.
http://home1.gte.net/res18h39/contrast.htm

AVS Member Supported Contrast Dabase
In this link (AVS Member Supported Contrast Database) an Excel spreadhseet is available for download which contains the data for current measurements for several interesting projectors. As the project goes forward, we hope that others will use the test patterns and measure their projector performance and add their results to this database. White level, black level and derived contrast for luminance ranging from 0.1-50% can be found for various projectors in this file.

A word on Intra-Scene Contrast
Ultimately intra-scene contrast (the contrast between different areas in a specific scene) is what is most important to people. Unfortunately the projector video gamma, spatial relationships and pixel luminance histogram complicate an attempt at equating test pattern derived contrast with real world video content. The test pattern contrast data is still very useful in providing a consistent benchmark for gauging technology differences between projectors but we are also working on relating this data to a few specific scenes to help people gauge how scenes with varying degrees of luminance affect contrast. To this end, Erik Garci has provided an intra-scene contrast calculator (http://home1.gte.net/res18h39/intrascene.htm) and we hope to integrate these few select scenes into this contrast project at a later date.

Contrast at 0 luminance
As mentioned earlier, these test patterns with varying degrees of luminance (% APL) allow contrast to be measured directly in a similar fashion as the traditional ANSI benchmark and we call this static contrast because both white and black points can be measured at the same time and the values don't change over time (ignoring bulb drift, etc). Attempting to directly measure static contrast at 0 luminance is of course impossible because there is no white content to relate to black. In the past, sequential full on/full off contrast was a useful equivalent for contrast at 0 luminance, however this breaks down for dynamic iris projectors because the iris can never be open (full white) and closed (full black) at the same time.

Contrast at 0% APL - a new definition
Because the full on (iris open)/ full off (iris closed) contrast is never achievable at the same time with a DI projector, it's useful to extrapolate what the contrast would be at 0 luminance by creating a new definition that we're calling contrast at 0%APL. This is defined as the measured white level at the smallest available luminance / measured full black. As can be seen from the charts below, this definition accurately portrays the contrast as one approaches 0 luminance for both dynamic iris and non DI equipped projectors.


The chart below graphically shows the problem trying to plot both DI and non-DI data when attempting to extrapolate contrast at 0 luminance using traditional sequential contrast




The chart below graphically shows how using the new contrast at 0% APL definition leads to accurate values for contrast at 0 luminance for both DI and non-DI projectors alike.




Plotted Contrast vs luminance


The chart below shows a sample of contrast vs luminance (using 0% APL definition) for various projectors as well as a sample of DI settings.



Relative White level and Relative Black Level vs Luminance
Because contrast is a relationship between white and black, it's useful to examine white level vs luminance and black level vs luminance independently to see how simultaneous deviations in both can affect overall contrast. Unfortunately, due to setup and measurement differences, absolute comparisons of white and black levels between projectors cannot be made. These graphs do the next best thing which is to normalize the black and white levels so that the change in black level or the change in white levels from 50% APL (ANSI) can be compared. Please don't assume that projector A or B has better black levels or whiter whites from these charts as this is not what this data is displaying. Instead it shows how the deviation in white or black level from 50% APL as a function of luminance is changing. As an example a person can see from this chart that the black level at full off has decreased from 50% APL by roughly similar amounts between the HD1 and the VW50 Iris 1. This graphically shows the benefit of enhanced black levels with this iris mode. The Relative White Level chart also graphically shows the drawback that this mode creates with white levels. Interestingly enough, the overll contrast curve shows how these two relationships work together to boost overall contrast over the non-DI mode.


The chart below shows relative white level deviation vs luminance for a few selected projectors (DI and non-DI)



The chart below shows the relative black level deviation vs luminance for a few selected projectors (DI and non-DI)



As a side note, it's also possible to very roughly extrapolate absolute black levels between the HD1 and VW50 Iris 1 mode from this relative black level chart because both have similar 50% APL (ANSI) performance. In other words assuming both projectors had equal brightnesses at full field white (full on), the black level at 50% APL will be roughly similar because their 50% APL contrast performance are similar. So, if they both have similar black levels at 50% APL then this black level performance chart shows us that the deviation from 50% APL (where they are both equivalent) will be fairly close at 0% APL and nearly 4x better than the VW50 with Iris off. I should point out that this exercise is not the purpose of this project or benchmark, but it is an interesting exercise nonetheless.

Final thoughts
This project is unique in one respect in that it's a public work in progess and is therefore subject to change and revision at any time. For example, no attempt has been made to relate this contrast data with intra-scene contrast or to gauge other important aspects of projector contrast such as DI behavior (outside of full open and fully closed apertures). But this doesn't mean that work along these lines won't be done at a later date.

To see the full discussion on this project and to provide comments, criticism and to add data to this project, please use this thread:

http://www.avsforum.com/avs-vb/showthread.php?t=761806

Mark Petersen's Avatar Mark Petersen 09:43 PM 01-04-2007
Contrast measured at the Screen: (TBD)
lovingdvd's Avatar lovingdvd 09:56 PM 01-04-2007
Mark - thanks for starting this. Does this graph include the results from the Sharp 10K I posted? I don't see it there, but I do see something labeled as 20K. Those don't look like the numbers I measured anyway, but I wanted to make sure you did not think my measurements where from a Sharp 20K.
lovingdvd's Avatar lovingdvd 10:00 PM 01-04-2007
Also what's the difference between the two readings for say the "JVC HD1" vs. "Model (HD1)"? Are these just where measurements were done at a particular distance from the lens but for the same pj? If so it may be best to pick one and plot just that.
Mark Petersen's Avatar Mark Petersen 10:12 PM 01-04-2007
Okay folks, here is some interesting data! Let's hear your take on what it all means!

A couple of points of clarification first:
1) The 0% APL description is defined as Reference white / Full Black. For a non-DI equipped projector it's close to Full White / Full Black (sequential contrast). But for a DI equipped projector Full White and Reference White aren't the same and we found that defining a new metric that we're calling "0% APL" is useful at describing what happens in dark scenes that approach full black.

On/Off Contrast is still a useful metric because it describes the full range of brightness to darkness, but for a DI eqiuipped projector the intra-scene contrast is better defined using the 0% APL metric.

2) 50% APL is actually not a test pattern but ANSI contrast. To be precise what's been used so far is Greg Rogers Modified ANSI CR method.

3) Preliminary Data for the VW50 at Iris Off is shown which doesn't include 15% and 20% APL test patterns. This will be corrected once Wm gets a chance to post more exact numbers.

4) The HD2K modeled values assume an ANSI CR of 100 which is probably fairly accurate, but Wm will hopefully be able to provide a final number after CES.
Mark Petersen's Avatar Mark Petersen 10:14 PM 01-04-2007
Quote:
Originally Posted by lovingdvd View Post

Mark - thanks for starting this. Does this graph include the results from the Sharp 10K I posted? I don't see it there, but I do see something labeled as 20K. Those don't look like the numbers I measured anyway, but I wanted to make sure you did not think my measurements where from a Sharp 20K.

Hi lovingdvd, I'm still incorporating your numbers and will revise the graph shortly. The "Model" terminology means using Erik Garci's contrast calculator. So we've graphed actual HD1 data versus the "Modeled HD1" which by the way takes as inputs on/off and ANSI CR values which were measured.
lovingdvd's Avatar lovingdvd 10:19 PM 01-04-2007
Quote:
Originally Posted by Mark Petersen View Post

Hi lovingdvd, I'm still incorporating your numbers and will revise the graph shortly. The "Model" terminology means using Erik Garci's contrast calculator. So we've graphed actual HD1 data versus the "Modeled HD1" which by the way takes as inputs on/off and ANSI CR values which were measured.

Oh, ok, gotcha. I think the modeled data may work better in a separate graph. Will you consider putting together one graph that has just the actual results for the pjs tested so far? I believe this will make it it more intuitive to look at the lines in the graph and compare the performance of measured pj results to one another.

Also which pj is the "20K"? I assume the HD20K but wouldn't want folks to mistake this for the Sharp 20K.

Thanks for all the hard work on this - this project is really starting to come together.
Mark Petersen's Avatar Mark Petersen 10:38 PM 01-04-2007
Quote:
Originally Posted by lovingdvd View Post

Oh, ok, gotcha. I think the modeled data may work better in a separate graph. Will you consider putting together one graph that has just the actual results for the pjs tested so far? I believe this will make it it more intuitive to look at the lines in the graph and compare the performance of measured pj results to one another.

Also which pj is the "20K"? I assume the HD20K but wouldn't want folks to mistake this for the Sharp 20K.

Thanks for all the hard work on this - this project is really starting to come together.

For now it's nice to have the modeled and measured data displayed simultaneously because one of the goals of this project was to validate the model (which appears to be the case). Down the road as we start collecting lots of data we may have to split it or perhaps just display graphed data on the projectors that are most interesting to people. We can figure that out later.

Also the "20K" means the Sharp 20K. Since this is modeled results it's true for any projector that has those values of on/off and ANSI CR (6000:1 on/off and 800:1 ANSI).
lovingdvd's Avatar lovingdvd 10:48 PM 01-04-2007
Quote:
Originally Posted by Mark Petersen View Post

For now it's nice to have the modeled and measured data displayed simultaneously because one of the goals of this project was to validate the model (which appears to be the case). Down the road as we start collecting lots of data we may have to split it or perhaps just display graphed data on the projectors that are most interesting to people. We can figure that out later.

Also the "20K" means the Sharp 20K. Since this is modeled results it's true for any projector that has those values of on/off and ANSI CR (6000:1 on/off and 800:1 ANSI).

Makes sense since the focus is to validate our approach at this point. I have a couple suggestions that may help. I think it would be cleared to change the legend to say "Modeled" instead of "Model" - as "Modeled 20K" makes it obvious that it is a simulated plot and not taken from a "model 20K".

Also I think it would help a lot if you could use the same color line for the modeled vs. actual results, but just changed the line style to dashes for the modeled on. So for example the yellow and magenta colors for the HD1 above would be shown both in say magenta, one dashed line and one solid. I think this would help improve on the areas I raised concern with while still keeping the data all on one chart for easy comparison purposes. Thanks.
Mark Petersen's Avatar Mark Petersen 11:26 PM 01-04-2007
So what are we learning from this data?

1) ANSI CR is an important measure of intra-scene contrast. Even a projector such as an RS1 with huge on/off CR has lower intra-scene contrast in the brighter scenes compared to a projector with very high ANSI CR.
2) On/Off CR is an important measure of black level but it dominates only the dark scenes.
3) Something very curious is happening between the VW50 Iris 1 and Iris Off modes. This is preliminary data, but it indicates that Iris 1 has better black level and better contrast in the dark scenes but the situation is reversed higher up the scale where Iris Off has significantly higher intra-scene contrast in the brighter scenes!
tryingtimes's Avatar tryingtimes 04:59 AM 01-05-2007
The VW50 graphs are very interesting - especially as most people prefer the iris 'auto1' setting. The fact that people prefer this image to the iris 'off' would suggest that the curve of the HD1(RS1) would be appealing in the same way.
Or at least that's how I've interpreted it
DIY Guy's Avatar DIY Guy 05:55 AM 01-05-2007
Hi Mark,

Any chance of adding a reference CRT plot for comparison? I'm still trying to wrap my head around this.

Thanks,
Thunder's Avatar Thunder 07:11 AM 01-05-2007
Wow, very interesting. Thanks Mark and crew for pulling this together.

Looking purely at the charts, it appears that the Sharp 20k is the clear winner as it delivrs a clear contrast edge on everything else above a 1 APL scenes. I found this very surprising. I assumed that the superior on/off contrast of the RS1/HD1 would have prevailed over a projector like the Sharp up to about 15 - 20 APL. So this has me rather confused based upon all of the folks who have commented on the superiority of the RS1 over the Sharp - after viewing both side by side. Further, many have commented that typical movie scenes are in the 15 to 20 APL range, noty 1 or less than one. If this is so, how could the RS1 compete with the Sharp or are thse graphs fundamentally disconnected with "real life"? Please help me understand what I'm looking at here.
lovingdvd's Avatar lovingdvd 07:35 AM 01-05-2007
Quote:
Originally Posted by Mark Petersen View Post

So what are we learning from this data?

1) ANSI CR is an important measure of intra-scene contrast. Even a projector such as an RS1 with huge on/off CR has lower intra-scene contrast in the brighter scenes compared to a projector with very high ANSI CR.

I'm not sure we can conclude that yet because I don't think we have hard evidence whether these patterns truly reflect real-world intra-scene contrast with real video/film content.

For example IIRC Greg Rogers stated flat out in another thread that he thought other aspects play a role in real intra-scene content beyond what these test patterns could simulate and was skeptical in general of these patterns for us in determining intra-scene CR for those reasons.

Quote:


2) On/Off CR is an important measure of black level but it dominates only the dark scenes.

Yes and that seems to agree with what I've always heard (that very high CR is needed to remove the haze from dark scenes).

Quote:


3) Something very curious is happening between the VW50 Iris 1 and Iris Off modes. This is preliminary data, but it indicates that Iris 1 has better black level and better contrast in the dark scenes but the situation is reversed higher up the scale where Iris Off has significantly higher intra-scene contrast in the brighter scenes!

Yes, I thought this was interesting too. So it would seem that a Pearl with the iris off would perform quite similar to a RS1 as far as contrast is concerned in the mid to upper end, and the RS1 would have the clear advantage at the low end (where it may matter most).

The other key difference however is that even if the CR is similar between the RS1 and Pearl in the mid to upper end, the RS1 would be much brighter overall because the Pearl's lumens are significantly less with the iris off (as far as I remember). Of course all this is highly speculative.
lovingdvd's Avatar lovingdvd 07:41 AM 01-05-2007
Quote:
Originally Posted by Thunder View Post

Wow, very interesting. Thanks Mark and crew for pulling this together.

Looking purely at the charts, it appears that the Sharp 20k is the clear winner as it delivrs a clear contrast edge on everything else above a 1 APL scenes. I found this very surprising. I assumed that the superior on/off contrast of the RS1/HD1 would have prevailed over a projector like the Sharp up to about 15 - 20 APL. So this has me rather confused based upon all of the folks who have commented on the superiority of the RS1 over the Sharp - after viewing both side by side. Further, many have commented that typical movie scenes are in the 15 to 20 APL range, noty 1 or less than one.

Thunder - good post. Keep in mind that the Sharp 20K data on the chart is modeled based on the Contrast Calculator. Hopefully someone with a Sharp 20K will take these measurements so we can see how it really pans out. Because the numbers are much higher based on specs for the 20K, it'll be interesting to see if the measured performance holds up.

Quote:


If this is so, how could the RS1 compete with the Sharp or are thse graphs fundamentally disconnected with "real life"? Please help me understand what I'm looking at here.

If I understood him correctly, Greg Rogers posted in another thread he thought that intra-scene contrast may not be modeled accurately with these patterns because other factors come into play for intra-scene CR with real-world images. We do not know the answer to this yet, but if indeed most people after comparing ideal 20K and RS1 setups conclude the RS1 is superior that would tell us for sure that these APL patterns are only giving us part of the picture.
Erik Garci's Avatar Erik Garci 07:42 AM 01-05-2007
Quote:
Originally Posted by Mark Petersen View Post

3) Something very curious is happening between the VW50 Iris 1 and Iris Off modes. This is preliminary data, but it indicates that Iris 1 has better black level and better contrast in the dark scenes but the situation is reversed higher up the scale where Iris Off has significantly higher intra-scene contrast in the brighter scenes!

What is the VW50's throw ratio in this case? I wonder how much difference there is at min throw versus max throw.

Do you have any measurements for Iris Min (in Manual mode)? I wonder how it compares to the other modes.
Erik Garci's Avatar Erik Garci 08:05 AM 01-05-2007
Quote:
Originally Posted by Mark Petersen View Post

For now it's nice to have the modeled and measured data displayed simultaneously because one of the goals of this project was to validate the model (which appears to be the case).

Since the model seems to be validated, I am thinking of making another web page, which will calculate the CR of actual movie scenes. I already made a spreadsheet that can do it, so it's just a matter of converting it into a web page. Please feel free to post sample images to the other thread.
Bob Sorel's Avatar Bob Sorel 08:21 AM 01-05-2007
I haven't been keeping up with the other thread, but where are these numbers coming from? I mean, is there a single person taking measurements of all of these projectors in the same room, with the same equipment, using the same technique, etc. like Greg Rogers does? Or are all of these numbers coming from different sources?

If the latter, I would caution people not to reach any conclusions prematurely...
lovingdvd's Avatar lovingdvd 10:37 AM 01-05-2007
Quote:
Originally Posted by Erik Garci View Post

Since the model seems to be validated, I am thinking of making another web page, which will calculate the CR of actual movie scenes. I already made a spreadsheet that can do it, so it's just a matter of converting it into a web page. Please feel free to post sample images to the other thread.

Sounds great!

In the other thread where we've been discussing the APL % patterns for these measurements, there's been some talk about how the 1% APL pattern may better emulate a 15% APL scene like the Gladiator one (as opposed to the 15% APL pattern). What do you think about this?
gremmy's Avatar gremmy 11:20 AM 01-05-2007
Is it accurate to say that the Pearl outperforms the new JVC in mid-to-bright scenes while the new JVC kicks its arse in dark scenes?

Am I reading this correctly?
lovingdvd's Avatar lovingdvd 11:29 AM 01-05-2007
Quote:
Originally Posted by gremmy View Post

Is it accurate to say that the Pearl outperforms the new JVC in mid-to-bright scenes while the new JVC kicks its arse in dark scenes?

Am I reading this correctly?

Not exactly. Although the graph shows the ANSI CR is about the same from 50% APL (standard ANSI CR pattern) and up, the theory behind this project is that its performance at the lower end (20% APL and lower) that makes the huge difference in intra-scene CR and hence picture depth.

I'm just throwing out some numbers here, but let's say for example that 80% of the depth and PQ related to CR comes from performance at 20% APL and lower. If the Pearl is slightly better above 50% APL and the RS1 is significantly better at 20% APL and below, then this is not a matter of one winning on the high and and the other winning on the low end.

At any rate I'm not sure why you are thinking the Pearl is better on the upper end as ANSI CR and up seems essentially the same.
GlenC's Avatar GlenC 11:35 AM 01-05-2007
Quote:
Originally Posted by gremmy View Post

Is it accurate to say that the Pearl outperforms the new JVC in mid-to-bright scenes while the new JVC kicks its arse in dark scenes?

Am I reading this correctly?

It seems to me that the very low APL performance is the one that makes watching the most enjoyable. Good brightness ancontrast in bright scenes give the picture some punch, but really seeing the low APL with some contrast making things more 3D at the low end is what makes it spectacular.

I was really taken in at CEDIA with the performance of the Meridian/Faroudja MF1, truly a performer.
Erik Garci's Avatar Erik Garci 12:05 PM 01-05-2007
Quote:
Originally Posted by lovingdvd View Post

Sounds great!

In the other thread where we've been discussing the APL % patterns for these measurements, there's been some talk about how the 1% APL pattern may better emulate a 15% APL scene like the Gladiator one (as opposed to the 15% APL pattern). What do you think about this?

I think the 1% APL pattern might emulate the Gladiator scene better than the 15% APL pattern emulates it. However, it does not necessarily emulate other 15% APL scenes better, since other scenes have different histograms.

Anyway, as I already pointed out in the other thread, the Gladiator scene is emulated much better by this pattern:

2.5 gamma
5% screen area covered by the checkerboard
90% checkerboard stimulus

which has a 2.25% APL, and an average luminance of about 2% or 3% (depending on the display).
lovingdvd's Avatar lovingdvd 12:20 PM 01-05-2007
Quote:
Originally Posted by Erik Garci View Post

I think the 1% APL pattern might emulate the Gladiator scene better than the 15% APL pattern emulates it. However, it does not necessarily emulate other 15% APL scenes better, since other scenes have different histograms.

Thanks. This makes sense, and I think this is what Greg was saying (or eluding to). So the real challenge seems to be that different scenes have different histograms and it may require creating multiple APL patterns for multiple histograms. And we can wind up with pj A that is better than B when it comes to a scene which histogram 1 vs. 2. Seems overly complex but it is a complex matter.

I see now what folks are talking about as far as selecting certain scenes to try and identify some common histograms. Perhaps from a small set of common histograms we can then design patterns that reflect those histograms?

I saw this because as far as I know there is no good way to measure an actual scene's real CR, is there? Doing so would require finding the darkest part of the image and measuring that, then doing the same for the brightest part. However because of uniformity issues with pjs or screens I imagine taking readings for the bright white part at say near the upper right concern and comparing that to the darkest region say near the middle would be skewing the results just based on where on the screen the measurements were coming from - wouldn't you think?
Mark Petersen's Avatar Mark Petersen 12:29 PM 01-05-2007
Quote:
Originally Posted by Erik Garci View Post

Since the model seems to be validated, I am thinking of making another web page, which will calculate the CR of actual movie scenes. I already made a spreadsheet that can do it, so it's just a matter of converting it into a web page. Please feel free to post sample images to the other thread.

Quote:
Originally Posted by Thunder View Post

Looking purely at the charts, it appears that the Sharp 20k is the clear winner as it delivrs a clear contrast edge on everything else above a 1 APL scenes. I found this very surprising. I assumed that the superior on/off contrast of the RS1/HD1 would have prevailed over a projector like the Sharp up to about 15 - 20 APL. So this has me rather confused based upon all of the folks who have commented on the superiority of the RS1 over the Sharp - after viewing both side by side. Further, many have commented that typical movie scenes are in the 15 to 20 APL range, noty 1 or less than one. If this is so, how could the RS1 compete with the Sharp or are thse graphs fundamentally disconnected with "real life"? Please help me understand what I'm looking at here.

This is an important point. This data shows that projector contrast can be easily meaasured and it is predictable. Every scene from every movie and video will fall somewhere along the contrast curve. Where it gets dicey is determining where a specific scene with a specific APL falls along the curve. Movie APL doesn't seem to translate directly to the APL used in these test patterns so I'm anxious to see some examples and thankful for the work that Erik is going to put into that.

Also to answer Thunder's point. I wouldn't be surprised that once the dust settles with regard to movie APL vs test pattern APL that most dark scenes fall well below the 5% APL test pattern. So the RS1 vs high ANSI DLP contrast debate could be focused on the relative merits of contrast performance in these specific scenes.

There is also a third component to this discussion which lovingdvd has provided data for but I haven't posted yet, which is that measured screen contrast will also play a huge role. In a given room, the the washout effect will act to compress the contrast differences between projectors and this is likely more pronounced at higher APL. So for real world viewing high On/Off CR may yet still play a huge role.

EDIT: I can see Erik and I are already thinking along the same lines. It might be the case that we need to add a few more low APL test patterns to sample the 0%-5% region a little better.
MrWigggles's Avatar MrWigggles 12:33 PM 01-05-2007
Mark, is this following stil the methodology proposed by William Phelps:

Quote:
These patterns are designed for a single probe placement. Display each in turn, take a reading and record it. Divide the "white" reading by each of the three "nPercent" readings. There is even a "target" pattern for help in placing the probe, and "black" and "fullwhite" patterns for collecting On/Off contrast measurements.

I don't think these tests can be done well with a single probe placement. A DI projector will always "win" because you aren't measureing the little white squares at the same time that you are measureing the center black region. At the low APL's on a DI projector, the little white squares aren't white anymore they are grey. You should be dividing grey/black not white/black to get an accurate reading.

For each image you need to measure both the little "white" squares and the center black and then divide out to find the ratio.

The image I posted with the square in the left corner was designed to be done all with one image. (The square in the corner has the benefit of taking non-uniformity out of the equation and allowing the metrologist to stand next to the screen without blocking the image.) However, multiple little square like in Williams' images are better, if you can get your meter on them.

In this new world of dynamic irises, sequential measurements are no longer valid - that's the downfall of On/Off measurements. You need to take two readings on the same image.

-Mr. Wigggles

Ps. measurements at the screen are likely to be invalid due to the black reading being at the limits of the lightmeter used. Measuring at the screen will also likely bring the room into play on the measurements. For determining the quality of someone's HT, screen measurement are fine; but for reviewing the projector, getting close to the projector is the best course of action.
Toe's Avatar Toe 12:35 PM 01-05-2007
Quote:
Originally Posted by gremmy View Post

Is it accurate to say that the Pearl outperforms the new JVC in mid-to-bright scenes while the new JVC kicks its arse in dark scenes?

Am I reading this correctly?


I am confused how you are reading it that way. The way I read it, they are very similar in the mid to bright scenes with the JVC having a slight advantage. In the dark scenes however, I agree the JVC is head and shoulders above the Pearl.
Mark Petersen's Avatar Mark Petersen 12:57 PM 01-05-2007
Quote:
Originally Posted by DIY Guy View Post

Any chance of adding a reference CRT plot for comparison? I'm still trying to wrap my head around this.

I do have a version that shows two CRT graphs, one with a typical calibration of 10,000:1 on/off and 130 ANSI CR and another "Super CRT" with 100,000:1 on/off and 130 ANSI CR. If there is interest I can post those. Is 130 ANSI CR typical for a CRT?

Quote:
Originally Posted by lovingdvd View Post

I'm not sure we can conclude that yet because I don't think we have hard evidence whether these patterns truly reflect real-world intra-scene contrast with real video/film content.

For example IIRC Greg Rogers stated flat out in another thread that he thought other aspects play a role in real intra-scene content beyond what these test patterns could simulate and was skeptical in general of these patterns for us in determining intra-scene CR for those reasons.

I missed greg's posts and will go back and read them. As I posted earlier the contrast performance of a projector should be readily measurable and predictable. In this era of high ANSI (but average on/off) and high On/off (but average ANSI) contrast projectors and manual Irises, dynamic irises, etc we need to get a better feel for the relative projector performance between the two contrast extremes of on/off and ANSI. So this project is useful for that reason alone. What is of most interest to people is determining where on the contrast curve a specific scene falls and this is an area where we should get a better feel for soon.

Quote:
Originally Posted by Bob Sorel View Post

I haven't been keeping up with the other thread, but where are these numbers coming from? I mean, is there a single person taking measurements of all of these projectors in the same room, with the same equipment, using the same technique, etc. like Greg Rogers does? Or are all of these numbers coming from different sources?

If the latter, I would caution people not to reach any conclusions prematurely...

All of the data coming so far is from Wm (HD2K, VW50 and HD1) and we have Sharp 10K data from Lovingdvd that I'm in the process of posting. So the data so far is using the same setup, equipment, etc.

When we start to add data from others our analysis will have to change accordingly. In other words we will need to look for trends, take into account equipment and setup, etc. If we are lucky enough to get say 5 different members to post results for projector X, we can look for deviations between members and apply statistical guides such as removing outlying data (or ask members to remeasure). I do agree with you though that this sort of data collection and interpretation is fundamentally different than data from a single consistent source. I do think that it's still meaningful and that it can be interpreted though, just that we have to be careful in doing so.
lovingdvd's Avatar lovingdvd 01:07 PM 01-05-2007
Quote:
Originally Posted by Mark Petersen View Post

There is also a third component to this discussion which lovingdvd has provided data for but I haven't posted yet, which is that measured screen contrast will also play a huge role. In a given room, the the washout effect will act to compress the contrast differences between projectors and this is likely more pronounced at higher APL. So for real world viewing high On/Off CR may yet still play a huge role.

Yes indeed. If we are thinking along the same lines - this is because on/off CR seems to be just as important and maybe more so at the 1% APL pattern level.

For instance if you look at the graph you will see that at 1% the modeled RS1 contrast is HIGHER than that of the modeled Sharp 20K despite the 20K having nearly 3x ANSI CR. [In actuality the RS1 measured below the modeled Sharp 20K, but we can't compare an actual to a modeled, as the Sharp 20K actual will likely fall under its modeled amount too].

At 2% it looks like the RS1 still has this advantage over the Sharp 20K, and maybe starting around 3% it equals out, and by 5% on up the Sharp 20K has the clear advantage.

However, as we've been discussing, if it turns out that 15-20% typical real scenes are equivalent to the results with the 1-2% APL patterns, then the RS1 would have an advantage over the Sharp 20K in this regard. The Sharp 20K would win above 5% but that may be the range which has least bearing on intra-scene perceived contrast.

Mark are we thinking along the same lines here?
gremmy's Avatar gremmy 01:09 PM 01-05-2007
Quote:
Originally Posted by Toe View Post

I am confused how you are reading it that way. The way I read it, they are very similar in the mid to bright scenes with the JVC having a slight advantage. In the dark scenes however, I agree the JVC is head and shoulders above the Pearl.

Oops, I got my colored lines mixed up. I am now reading it the same way that you are.
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