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post #361 of 712 Old 12-09-2013, 12:45 PM
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Quote:
Originally Posted by DrFaxe View Post


it also depends on the settings and mode You're using. As a LS HCL customer + TEDs disc I use DIP mode with meter integration time of 1.04s (DIP time 4s). With this settings the probe can not read the mll of my display, but it accurate enough for stimulus levels >10% (maybe 5% too). To get the meter reading the mll correctly I have to use integration time of 6s but than I will loose the speed advantage completely.
So for this particular case it would make sense to enter the black level manually, without guess work.

And regarding gamma, I can not understand why You all stick on 2.2. The main reason I purchased LS was to calculate several targets without running a calibration over and over again, so I have 4 different gamma targets in my Radiance and just use a gamma setting the movie looks best to me (most times 2.25 or 2.3). rolleyes.gif

you can use whatever Gamma you like.... disc mediums are mastered with 2.2 mostly...

regarding the customization, I was referring to manipulating any probe/profile/LUT data in LS any way I see fit... all of this is possible in LS if u know how....

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post #362 of 712 Old 12-09-2013, 12:49 PM
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Originally Posted by smedith View Post

Your quoted maths makes no sense.  If you are going to give mathematical proof to back an argument, please can you make it more accurate?



In an 8 bit system, going to a ideal monitor with a perfect power function EOTF, then assuming normalized luminance, the code value 1 produces  0.000001617 = (1.0 / 255) ^ 2.4 of the luminance.



If it is a real monitor, then code value 0 will not produce 0 Cdm-2, but minimum luminance.  So, code value 1 must produce min +( (max –min) x 0.000001617).



This shows that the minimum step in luminance (code 0 to code 1)is dependant only on the physical transfer function of the display, not its minimum and maximum luminance values.



If you then use a software LUT to manipulate this further, then this minimum step value from 0 to 1 must get worse due to quantization error.  A BT.1886 calibration is based on the actual characteristics of the monitor, min and max luminance.  The black value “b” is just an offset.  Once the offset has been removed the power function should them be applied.  You could increase the offset in the LUT, but this makes no sense at all!!



I would be happy to keep discuss further, but I would appreciate it if you could tone your replies in a more professional way.  If this is the tone your company takes on an open forum with a potential new customer, it makes me question if I should actually purchase your product for my facility.



I will sign off this thread now.  As a last note I would say, there are may correct ways to implement BT.1886, which are valid and to the standard.  Just because one tool does it differently to another does not make it wrong just because you don’t understand how they do it.  It serves no professional integrity to just bash on a competitor and shout loud in public just because they are different.  I will now do further research into LS to see if it fits my needs before I commit.


thanks for sharing

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post #363 of 712 Old 12-09-2013, 12:50 PM
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Just by way of illustration, here is our hypothetical display near black luminance response (actually measured at levels used in the previous example). Plotted on a relative scale.


Simple power offset and scaling (target = 2.35)
Levels below 4% are clipped severely compressed.



BT. 1886 offset and scaling, technical gamma = 2.4,
(a,b) offset and scaling using Lb =0.05 cd/m^2, Lw = 120 cd/m^2
1-6% level response shows no clipping and good progression to mll:



LS provides no mechanism to emulate the BT.1886 EOTF that will generate the luminance response shown in the bottom plot. You are currently stuck with the top one if your display has a raised black level and you select their "BT.1886" option. The amount of clipping compression present will depend on the actual black level, the above was measured at 0.05 cd/m^2
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post #364 of 712 Old 12-09-2013, 01:36 PM
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Quote:
Originally Posted by smedith View Post

Thanks for your reply.  As you can tell, I am new to this forum, so I am sorry if I have offended your position in some way, but I think your response was a bit harsh.  That said, I am not a novice to this area.

I don't intent do offend you, but Steve is spreading misinformation. There is quite a history of him slandering the product my company produces, which may create an unintentional edge in my communications.

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Your quoted maths makes no sense.  If you are going to give mathematical proof to back an argument, please can you make it more accurate?
Sure.
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In an 8 bit system, going to a ideal monitor with a perfect power function EOTF, then assuming normalized luminance, the code value 1 produces  0.000001617 = (1.0 / 255) ^ 2.4 of the luminance.
Minor mistake on your part, it's 1/219, nominal black is code 16, nominal white is 235, but otherwise accurate enough.

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If it is a real monitor, then code value 0 will not produce 0 Cdm-2, but minimum luminance.  So, code value 1 must produce min +( (max –min) x 0.000001617).
Yes that is the exact formula I used for the power+offset I used above.
target for bit 18 = 0.05 + ((100-0.05) * ((2/219)^24)) = 0.051274 cd/m^2 target
target for bit 20 = 0.05 + ((100-0.05) * ((4/219)^2.4)) = 0.056724 cd/m^2 target

Step difference from 18 to 20 is only 0.0054 cd/m^2

Quote:
This shows that the minimum step in luminance (code 0 to code 1)is dependant only on the physical transfer function of the display, not its minimum and maximum luminance values.
I'm not sure what you mean by "dependant only on the physical transfer function of the display". While the ability for a display to accurately re-procedure an image certainly depends on out of the box physical characteristics, the discussion revolves around how to calculate the targets for calibration.

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If you then use a software LUT to manipulate this further, then this minimum step value from 0 to 1 must get worse due to quantization error.  A BT.1886 calibration is based on the actual characteristics of the monitor, min and max luminance.  The black value “b” is just an offset.  Once the offset has been removed the power function should them be applied.  You could increase the offset in the LUT, but this makes no sense at all!!
I can only guess this makes no sense, because you are not following the actual formula.



So lets walk through calculating bit 18 and bit 20 (10bit code 72 and 80).

Lw = 100
Lb = 0.05
γ = 2.4
a = (100^(1/2.4) - 0.05^(1/2.4)) = 0.92451294
b = (0.05^(1/2.4)) / (100^(1/2.4) - 0.05^(1/2.4)) = 0.043980823

For bit code 72 (10 bit)
V = 0.00913242009132420091324200913242

For bit code 80 (10 bit)
V = 0.01826484018264840182648401826484

Solving L = a(max[(V+b), 0])^γ
For 72, 0.9245 * ((0.009132 + 0.04398) ^ 2.4) = 0.0786 cd/m^2
For 80, 0.9245 * ((0.018265 + 0.04398) ^ 2.4) = 0.1151 cd/m^2

The size of the step between the two = 0.0364 cd/m^2
So BT.1886 correctly implemented produces a step size between these two points 7x greater than straight power with an offset.

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I would be happy to keep discuss further, but I would appreciate it if you could tone your replies in a more professional way.  If this is the tone your company takes on an open forum with a potential new customer, it makes me question if I should actually purchase your product for my facility.
I apologize for coming across as harsh, but as you can see, there is ZERO room for interpretation. Steve's assertion that his way is correct and his berating of valuable contributors to this forum is beyond frustrating.

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I will sign off this thread now.  As a last note I would say, there are may correct ways to implement BT.1886, which are valid and to the standard. 
I respectfully disagree. The standard says that Annex 1 fully describes the recommended formula. As I have demonstrated, the formula does not leave any variable undefined or subject to interpretation.

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Just because one tool does it differently to another does not make it wrong just because you don’t understand how they do it.  It serves no professional integrity to just bash on a competitor and shout loud in public just because they are different.  I will now do further research into LS to see if it fits my needs before I commit.
Once again I have to disagree, this is a well defined specification. This isn't the difference between subjective methods. For instance they use a very different 3D interpolation algorithm than we do. Is theirs good? Of course it is. You can get great results with their product. Is ours better? I firmly believe it is. But we aren't discussing something subjective here. The implementation of BT.1886 is either correct or incorrect. I would question a vendor that when shown they are incorrect, bashes the intelligence of those trying to express the need for accurate tools.

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post #365 of 712 Old 12-09-2013, 02:50 PM
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Quote:
Originally Posted by Manni01 View Post

I discussed this very point with Steve and his calibration expert at length about 6 months ago and they were both adamant that black compensation wasn't part of the BT1886 specs and that a power 2.4 gamma was the correct way to do this.

They must have read some other BT.1886 spec. from everyone else then. The whole point of BT.1886 is to deal with a non-zero reproduction black.
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post #366 of 712 Old 12-09-2013, 03:02 PM
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Originally Posted by Light Illusion View Post

Question away...
The annex is NOT part of the specification - as I have repeatedly stated.
Wow - your understanding of standards is way different to mine then. BT.1886 is a recommendation (That's why it's called "Recommendation ITU-R BT.1886" right there on the title page), it's scope is stated to be "This Recommendation specifies the reference electro-optical transfer function (EOTF)..." and the only two recommendations that it contains are defined by Annex 1 and Annex 2 and both define EOTF's. So to say they are not part of BT.1886 is simply outright nonsense.
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post #367 of 712 Old 12-09-2013, 03:31 PM
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Originally Posted by gwgill View Post

Wow - your understanding of standards is way different to mine then. BT.1886 is a recommendation (That's why it's called "Recommendation ITU-R BT.1886" right there on the title page), it's scope is stated to be "This Recommendation specifies the reference electro-optical transfer function (EOTF)..." and the only two recommendations that it contains are defined by Annex 1 and Annex 2 and both define EOTF's. So to say they are not part of BT.1886 is simply outright nonsense.

Indeed.



The meat of the spec is that Recomendation ITU-R BT.1886 and I quote,
"recommends
1 that the reference EOTF for displays usedin HDTV production and programme interchange
should be the one specified in Annex 1; "

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post #368 of 712 Old 12-09-2013, 03:40 PM
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Originally Posted by Iron Mike View Post

you can use whatever Gamma you like.... disc mediums are mastered with 2.2 mostly...

regarding the customization, I was referring to manipulating any probe/profile/LUT data in LS any way I see fit… all of this is possible in LS if u know how....

From reading so long of this forum and especially the Spears & Munsil thread, it does puzzle me why the creator of that disc? appears… to be quite adamant on 2.4.

http://www.avsforum.com/t/1442511/spears-munsil-hd-benchmark-blu-ray-2nd-edition/390#post_23839195

I keep reading so many people with different views and more so some others try to make it concrete that such and such is it.


Is there an official list of films and what they use?


Doug was right. A good balance is 2.25. I'm just curious to see if there is a list.
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post #369 of 712 Old 12-09-2013, 03:47 PM
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Originally Posted by Iron Mike View Post


dude, what planet are you on ?
On a planet where Karma has caught up with you ? There you were, casting doubt on the trustworthiness of all other color management systems when it came to implementing standards correctly or not, and it appears that it is in fact your beloved LS that is the only one that hasn't implemented an important standard properly! :-)

All I can say is that, given how complex some of these system are, we all make mistakes, but the best thing to do when faced with proof positive is to admit we got it wrong, fix it, and move on.
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Originally Posted by gwgill View Post

we all make mistakes, but the best thing to do when faced with proof positive is to admit we got it wrong, fix it, and move on.

Unless you're Obama.
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post #371 of 712 Old 12-09-2013, 04:01 PM
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should be direct linking to the document and referencing page/section/part#

A do not reproduce line

See copyright at bottom of page 2 at http://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1886-0-201103-I!!PDF-E.pdf

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post #372 of 712 Old 12-09-2013, 04:04 PM
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1. Re: "I don't intent do offend you, but ...."

Yes you do, you've the attack dog ... no secret, everyone knows this ... you never care about of the consequences of your statements ... I seen this same deplorable behavior on the Chromapure threads with Tom Huffman ... and I've noted your false apologies there as well ... nothing will ever change.

2. Re: "I apologize for coming across as harsh ... Steve's assertion that his way is correct and his berating of valuable contributors to this forum is beyond frustrating."

You have an intolerant point of view ... and you do not even realize it. You never have spent any time trying to understand someone else's point of view. It's your way or the highway.

3. Re: "I respectfully disagree. The standard says that Annex 1 fully describes the recommended formula. As I have demonstrated, the formula does not leave any variable undefined or subject to interpretation. Once again I have to disagree, this is a well defined specification. This isn't the difference between subjective methods. For instance they use a very different 3D interpolation algorithm than we do. Is theirs good? Of course it is. You can get great results with their product. Is ours better? I firmly believe it is. But we aren't discussing something subjective here. The implementation of BT.1886 is either correct or incorrect. I would question a vendor that when shown they are incorrect, bashes the intelligence of those trying to express the need for accurate tools."

Congratulations: First time I could read an objective statement from you with out you expressing an intolerant point of view of others. Did somebody else write this for you? loooooooool

Wrap Up: Everyone, including your lap dogs, understand you are trying to slow down Steve and his Light Space product. Putting an anchor and chain on Steve and the Light Space Product is like putting an anchor on wave that surfers ride on the coasts of Hawaii. Steve and his company is riding the wave of the future. They are surfing with the wave. You are swimming upstream and running head on into these waves. It's painful and everyone understands this. Simply turn around and surf the wave of the future with the rest of us. We are all learning what Light Space is all about because they are soooo far ahead of us or anything I've learned about Studio or in the THX or ISF classes. I would suggest buying Light Space and using the tools ... oh, I forgot, your company tried to buy the Light Space Product a couple of years ago because you thought is was so great back then ... so, what has changed between then and now? It still is the same great product, but with many more added features. I'll respond tomorrow to your reply. Have to watch a movie with a Light Space calibrated Epson 6020 projector with eeColor. Respectfully and tolerably submitted: JJ:D
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post #373 of 712 Old 12-09-2013, 04:18 PM
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Quote:
Originally Posted by turbe View Post

should be direct linking to the document and referencing page/section/part#

A do not reproduce line

See copyright at Bottom of coverpage

The excerpts used should be allowed under fair use policy (in the U.S. anyway). It's also freely available (no fee).
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post #374 of 712 Old 12-09-2013, 04:20 PM
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Originally Posted by turbe View Post

should be direct linking to the document and referencing page/section/part#

Should fall under fair use.
http://www.copyright.gov/fls/fl102.html

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post #375 of 712 Old 12-09-2013, 04:31 PM
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Originally Posted by Carbon Ft Print View Post

Wrap Up: Everyone, including your lap dogs, understand you are trying to slow down Steve and his Light Space product.
Actually, it's just that there comes a point where the huge wave of marketing spin is causing harm to everyone, particularly when it goes to the extremes of telling people that black is white, and some attempt at bringing it all down to earth again is worth it. The cold water in the face may be a shock, but ultimately it will be refreshing.
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post #376 of 712 Old 12-09-2013, 04:41 PM
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Originally Posted by gwgill View Post

On a planet where Karma has caught up with you ? There you were, casting doubt on the trustworthiness of all other color management systems when it came to implementing standards correctly or not, and it appears that it is in fact your beloved LS that is the only one that hasn't implemented an important standard properly! :-)

All I can say is that, given how complex some of these system are, we all make mistakes, but the best thing to do when faced with proof positive is to admit we got it wrong, fix it, and move on.

Gill, your level of ignorance never stops to amaze me... do you actually READ other posts ? I know your BFF Zoyd doesn't, but man you should know better... clearly, you don't... READ and UNDERSTAND other posts...

what you stated here partly, is exactly what I stated (in the other thread), the reason we cross validate results from ALL applications is because we don't trust ANY solution (strictly as a top level QC approach)... that would include LS... so as everyone knows here, we profile in LS and cross validate in other apps... u seem to be very confused, or again simply ignorant...

in addition, using multiple applications in the pre/post profiling process naturally gives you the best of all worlds... you wouldn't understand, u're blinded by the illusion that your hobbyist program is perfect... looking at the bug fix history of Argyll, makes me wonder why you think that... eek.gif

beyond that, in any enterprise level, result driven environment you need to evaluate all options all the time... you wouldn't understand, you don't work on that level... RESULTS matter, not what you or Zoyd THINK and ASSUME what you "might" have done like other PRO solutions...

the posts you made here including the ones from Zoyd made us downgrade ur solution from HOBBYIST to EXPERIMENTAL...

not that it actually matters, no Pro is using ur app anyway.

Hope this helps. wink.gif
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Quote the partial text for discussion here is one thing, posting image of a page from the document is another, even more so to the strong wording to the contrary.

Requests for republishing (and questions about copyrights) can be sought via: sales@itu.int
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post #378 of 712 Old 12-09-2013, 05:13 PM - Thread Starter
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Lumagen Radiance XE/XE+/XE3D/XE/XE+/XE3D/Mini-3D/XD/XD3D New 120313 Firmware Update

Release Notes

Fix for some older HDMI/DVI displays (particular case was a DPI Titan 250) not showing video with last two firmware revisions (112513-120213).

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post #379 of 712 Old 12-09-2013, 05:28 PM
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Quote:
Originally Posted by turbe View Post

Quote the partial text for discussion here is one thing, posting image of a page from the document is another, even more so to the strong wording to the contrary.

Requests for republishing (and questions about copyrights) can be sought via: sales@itu.int

Thanks turbe, I will write to the public affairs office with a summary of the discussion and use of screenshots in lieu of written quotes with citations. I will also of course inform them of the improper use of the specification in a commercial product.
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post #380 of 712 Old 12-09-2013, 05:32 PM
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Originally Posted by Iron Mike View Post

... you wouldn't understand, u're blinded by the illusion that your hobbyist program is perfect... looking at the bug fix history of Argyll, makes me wonder why you think that... eek.gif
You seem to be trolling. What other put downs, not based on any actual objective evaluation at all, can you come up with ?

Are your prepared to post the bug track database of LS for scrutiny ?
Not that it would be comparable - ArgyllCMS has a much longer history, and covers a much wider scope.
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not that it actually matters, no Pro is using ur app anyway.
Gee, I'll have to tell the guys at AMPAS that they're just a bunch of hobbyists then - Iron Mike said so. I'm sure they'll be devastated.
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Hope this helps. wink.gif
And bung a few :-)'s on the end, because "no offense".
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post #381 of 712 Old 12-09-2013, 05:35 PM
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Quote:
Originally Posted by turbe View Post

Quote the partial text for discussion here is one thing, posting image of a page from the document is another, even more so to the strong wording to the contrary.

Requests for republishing (and questions about copyrights) can be sought via: sales@itu.int
Given that the document is freely available from the ITU to anyone with an internet connection, I'm not sure that they'll be that interested. This isn't something from ISO.
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post #382 of 712 Old 12-09-2013, 05:38 PM
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Quote:
Originally Posted by gwgill View Post

Actually, it's just that there comes a point where the huge wave of marketing spin is causing harm to everyone, particularly when it goes to the extremes of telling people that black is white, and some attempt at bringing it all down to earth again is worth it. The cold water in the face may be a shock, but ultimately it will be refreshing.

Marketing spin eh? Nothing against you. I haven't used your product nor anything cryptic like it since the World Wide Web appeared. However, "marketing spin" just touched me off. So here's some to digest!!!! This is my contribution to this far flung off topic, attack dog thread.

I have seen this - talk about elusive advertising......: The following is a SpectraCal press release, bold emphasis and color by me
.
SpectraCal and Flanders Scientific Announce 3D LUT Calibration for FSI Broadcast Monitors

CalMAN Studio release provides unsurpassed accuracy with unprecedented speed

April 8, 2013

(Las Vegas, NV) – April 8, 2013 –Flanders Scientific and SpectraCal, Inc. announced today full 3D LUT calibration support for Flanders Scientific FSI broadcast monitors in SpectraCal’s software CalMAN Studio.

ColorCube (3D LUT) correction ensures the color and grayscale accuracy needed by color professionals in broadcast, production, and post-production. These professionals make color decisions based on what they see on their monitors, so they need to know with certainty that what they see on the screen is as accurate as possible.

“Flanders Scientific has long played an admirable role in educating the market about the importance of accurate images displayed in accordance with industry standards, and SpectraCal is pleased and honored to become part of their solution for giving customers the most accurate video representation possible,” said Derek Smith, SpectraCal’s founder and Chief Technical Officer. “We’ve long used CalMAN as a final quality control check to ensure every monitor is properly calibrated before shipping” said Bram Desmet, General Manager at Flanders Scientific. “We’re pleased to be able to expand upon this now with CalMAN’s new ability to allow users to generate 3D LUT based calibrations for direct import to any FSI monitor equipped with our advanced Color Fidelity Engine,” Desmet said.

A Flanders Scientific FSI broadcast monitor calibrated with CalMAN Studio is on display in SpectraCal’s booth at the National Association of Broadcasters (NAB) annual convention in the Las Vegas Convention Center April 8-11. SpectraCal is showing the FSI monitor in Booth SL 15716, along with CalMAN ColorChecker, also released today. Using ColorChecker, visitors can see for themselves how accurate the CalMAN calibration is.

SpectraCal says that the version of CalMAN Studio released today offers an accuracy of monitor characterization never previously attainable, while requiring less time than any previous solution. CalMAN Studio characterizes a display in detail and creates a characterization cube, also known as a 3D look-up table (LUT), to compensate for the monitor’s deviations from a reference standard. The Color Fidelity Engine in the Flanders Scientific monitor applies the cube to the signal, allowing video professionals to be sure they are seeing exactly the same image on all monitors.

Flanders Scientific is introducing five new monitors at NAB. All five have the Color Fidelity Engine. Models including the Color Fidelity Engine include the LM-2461W, LM-2460W, CM320TD, CM240, CM171, CM170, BM230, BM210. CalMAN Studio is based on technology originally developed in SpectraCal’s display calibration solution used by nearly every professional calibrator today. Several technological advances lead SpectraCal to claim that CalMAN Studio provides more accurate monitor characterization than any software previously available. CalMAN Studio is available for free download evaluation from http://studio.spectracal.com/downloads. ;

About Flanders Scientific

(Flanders Scientific, Inc. is a US Based Company with headquarters in Suwanee, GA, just 30 minutes outside of Atlanta. FSI is focused on providing high performance professional broadcast and post production equipment at industry leading prices. FSI was started by industry professionals with over 25 years of experience in professional broadcast monitors and test/measurement equipment. For more information, visit www.flandersscientific.com.


SpectraCal certainly makes it look like CalMAN is FSI's software of choice and if I didn't already know better I'd probably assume that CM is what FSI uses to calibrate their monitors prior to shipment

But the truth is that "final quality control check" is graphs only.

The software used by Flanders to calibrate FSI monitors capable of holding and processing 3D LUTs is none other than --you already know, don't you - yes, it's LightSpace. That press release borders on, but is not quite due to clever words, false advertising.

I could puke.... mad.gif
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post #383 of 712 Old 12-09-2013, 05:58 PM
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Marketing spin eh? Nothing against you.
Like "out algorithms are beyond algorithms" "we don't use interpolation" "BT.1886 is a pure power curve" - and that's just the recent stuff.

I'm sure LS is a really good product with some really good people behind it, and lots of end users really like it, with good reason. They seem to have been very successful in introducing modern color management techniques to the Video industry, and have reaped deserved rewards for their efforts. But to carry on like they invented color management is pure marketing BS, so don't be upset when they get called on it.

If the SpectraCal marketing department is getting out of control too, then it's great to see them called on it as well
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post #384 of 712 Old 12-09-2013, 06:02 PM
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As a paid owner of Lightspace, I appreciate the efforts that mann01, zoyd, et al are making with trying to clarify the BT1886 colorspace conversion within the software. I have generated LUTs for BT1886 and have also made the same observation mann01 did with it being the same as a Rec709 2.4 gamma conversion. The labeling of the BT1886 conversion is somewhat disingenuous due to it not offering anything unique that a standard Rec709 2.4 gamma doesn't already provide. I don't really know about the history of competition within this product space, but it's clear that there are some passionate posters on all sides. Anyways, I look forward to trying out the new conversion option that will include the annex formula without having to re-profile my display.
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post #385 of 712 Old 12-09-2013, 06:27 PM
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Cant we all just get abong...wink.gif
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post #386 of 712 Old 12-09-2013, 06:53 PM
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Cant we all just get abong...wink.gif

Let's move to Colorado. tongue.gif

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post #387 of 712 Old 12-09-2013, 10:32 PM
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gotta say ironmike, you come across as extremely childish in these discussions. And this has nothing to do with the correctness or incorrectness of your arguments.

I'm inclined to agree that you're trolling here.

Whew... yeah... I gotta agree. I've not read much like that on any forum. Regardless of who is right, that's just a cat-fight... nothing of use to anyone... absolutely nothing.
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post #388 of 712 Old 12-10-2013, 02:52 AM
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Hi Sotti and Zoyd

 

Again, thank you for your reply.  I have to say, as my first experience of this board I have been a bit surprised by the level of anger and aggressiveness from many parties.  My aim in joining is to both learn and share, not to prove I know best or to listen to others who believe they know everything.  I have much experience in this area of research, but less in the details of home cinema implementations.

 

 

Firstly I will address Zoyds diagrams

 

The first shows, as described, how a pure gamma function is clipped as it heads to black.  This is NOT a property of a gamma function, but an artifact created by its in correct use.  The graph shows what happens if you try to pin code 0 to 0 luminance and code max (255 in an rgb  8 bit system) to max luminance then force the display to have a gamma of 2.4.  It can not reproduce the very low luminances as shown by points 1,2,3,4 on the graph.  It has a minimum luminance, so it is clipped.  You can see the ideal curve, grey plotted, going to absolute zero luminance.  This clipping proble is caused by measuring and processing absolute luminance values.  It is a poor, incorrect use of a gamma function to calibrate a display, not a demonstration that pure gamma is incorrect.  It is more correct to map the pure gamma function between minimum and maximum luminance, not zero luminance and maximum luminance.

 

The second diagram shows a BT.1886 calibration.  This does not show clipping. This is because BT.1886 maps a gamma function between minimum and maximum luminance.  It is not because BT.1886 has some sort of special formula.  What this is doing is allowing an absolute luminance measuring system to create a relative gamma curve, no more, no less.

 

These two diagrams show that an absolute measurement system can be tripped up by trying to implement a pure transfer function as it incorrectly tries to force code value 0 to absolutely zero luminance.  If you are using a relative measurement system, were you always subtract a black offset and normalize to maximum luminance, you never see this error in for a pure gamma function as it is correctly mapped between minimum and maximum.  As BT.1886 is doing the same thing, then it must also simplify to a pure gamma.  That’s just maths and understanding the difference between a relative and absolute system implementations.

 

 

Secondly I will address Sotti

 

I have no interest in your ongoing dispute with LightSpace and may be other vendors.  All I care is that a system that I purchase works, works well and is correctly implemented.  I totally agree that the standard document you referenced is not up for negotiation.  It is a standard and that’s that.  What I said is that the standard can be correctly and to standard, implemented in many different ways.  If you are in an absolute or relative measurement system, then to keep to standard, the implementation must be different to achieve the correct result.  This is an engineering fact not an excuse that you have implemented it wrong.  You must understand how to interpret a standard before you implement it, not just copy the maths verbatim.

 

While your maths is correct for your numbers you picked, it tells only a narrow part of the story.  It is clear you are looking at this from an absolute measurement perspective (as are the graphs from Zoyd).  If your system is relative, then all you have typed is a mute point.

 

Also, 16-235 is the scale for the Y component of standard definition Y, Cb,Cr digital video, not the luminance scale for the colour channels.  My example was 8 bit RGB which is simpler to understand for may home users.  As a note, the value 16 should not map to zero luminance.  Digital video has valid but not legal codes from 15-1 (0 is a control code) which represent video under shoot, an artifact from old school analogue video.  These represent sub-blacks.  Again, this is there to lift picture content above the place were black issues create visual artifacts.  This is some times known as REC709, which is not absolutely correct.  Looking at the standard for REC709 you will see the display primaries defined as CIE x,y values.  You will also see the transfer function defined as a gamma with a lower linear segment.  This transfer function is a CAMERA ONLY function, and is not defined for a display at all in the standard.  This is one contributing reason BT.1886 was needed.

 

To conclude, I do not think either Sotti or Zoyd are wrong, or right.  From their point of view they are sort of right.  What I am saying is that standards are set in stone, but that you can implement them in many ways and still be standard compliant.  I do not know for sure, but I suspect CM is an absolute system and that LS is a relative system.  May be their officials can confirm this as long as they don’t think this is commercially sensitive information.

 

I hope to stay on this board and both learn and contribute, but for a first experience, this has left me feeling a bit battered.

 

Bye for now

 

Regards

 

Smedith

 

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post #389 of 712 Old 12-10-2013, 03:10 AM
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@smedith: again, thank you for taking the time to share this.

calibration & profiling solutions: Lightspace, Spaceman, Calman, Argyll, ColorNavigator, basICColor
profiling & calibration workflow tools: Display Calibration Tools
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You are most welcome

 

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