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Spears & Munsil HD Benchmark Blu-Ray 2nd Edition - Page 20

post #571 of 636
Thanks for the clarification. I don't mean to be stubborn, but why is the inverse camera gamma not relevant?

Are you saying that having a (roughly) inverse relationship between encoding and decoding is useful, but that our primary concern should be with display gamma, since it is the display gamma, and the display gamma alone, that determines the lightness function of the display?

(with the corollary that having a good lightness function is the most important thing, and that we can always adjust our encoding gamma to "match" a desirable display gamma)
post #572 of 636
Quote:
Originally Posted by spacediver View Post

Thanks for the clarification. I don't mean to be stubborn, but why is the inverse camera gamma not relevant?

Because the image the viewer sees is the product. The process used to produce that image is interesting, but sort of irrelevant. Once the image is stored, it's now a screen-referenced image. We already know we're not trying to recreate the exact lightness curve of the actual scene, which is why BT.709's gamma isn't an inverse of the CRT gamma. So the actual light values of the original scene are no longer relevant; only the light values that we expect to see on the display.

If we were trying to recreate the actual scene viewed by the camera, we'd make sure the encoding and decoding curves were exact inverses of each other. We didn't, because we realized that having a positive end-to-end gamma looks better. It's kind of a poor man's appearance model.

The important curve is the display curve. The camera curve needs to be built with an understanding of the display curve, but not the other way around. In a sense you can think of the camera curve as the inverse of the display curve, plus some "special sauce" that fixes and adjusts some things for aesthetic or technical reasons.

For content generated originally in a computer, the camera curve is completely irrelevant. That content was generated, adjusted, tweaked, etc. on a computer screen, and you just want it to look right on the destination screen. The aesthetic tweaks built into BT.709 do not need to apply. The content was generated in the same environment that it's going to be viewed. So in that case, the inverse of the display curve is the relevant curve, not the camera curve. There really is no realm where the inverse of the camera curve is useful.

Ultimately the SMPTE engineers didn't make a spec for display gamma because it wasn't thought necessary. CRTs just were what they were; no gamma spec was considered important. The camera, on the other hand, needed a bunch of circuitry to make the image look good on the display, so that needed to be standardized.

Now, we're in a world where content comes from lots of different places besides a flat-lit studio, and displays have all kinds of different inherent electro-optical transfer functions, so a display standard is needed. And it makes sense for that standard to be based on what a CRT did, because that was the de-facto standard for years.
post #573 of 636
Quote:
Originally Posted by dmunsil View Post

If we were trying to recreate the actual scene viewed by the camera, we'd make sure the encoding and decoding curves were exact inverses of each other. We didn't, because we realized that having a positive end-to-end gamma looks better. It's kind of a poor man's appearance model.

The important curve is the display curve. The camera curve needs to be built with an understanding of the display curve, but not the other way around. In a sense you can think of the camera curve as the inverse of the display curve, plus some "special sauce" that fixes and adjusts some things for aesthetic or technical reasons.

yep I think we're on the same page then. And my reading of poynton (1993) led me to same conclusion about thinking of encoding gamma as inverse of display gamma, rather than the other way around.
Quote:
Originally Posted by spacediver View Post

Yes, it was naturally decoded by the CRT. It was never explicitly formulated into a recommendation, and was never "programmed" into the displays.

The recommended encoding function for video was, as I understand it, defined precisely because of the way CRTs worked.

As for the end to end of 1.1 /1.2, I've come across a couple flavours of reasoning

1: It is more pleasing to the eye

2: (image appearance model idea): In a dim surround, your eyes will be adapted to a lower background luminance, and will therefore be more sensitive. We therefore use a slightly higher decoding gamma to compensate. Or, more accurately, we use a slightly higher encoding gamma (gamma pre-correction) to compensate for our display gamma.

I take it 1) is because of 2).
post #574 of 636
Quote:
Originally Posted by SOWK View Post

This is ridiculous.

Do we have a "standard" or not?


2.22 has always looked correct to me.
2.4 is to contrasty to me
I have not tried bt.1886 yet.

I found comments interesting from Josh Pines, Technicolor VP of Imaging Research & Development at the Hollywood Post Alliance first-ever Reference Monitor Symposium, sponsored by Walt Disney Studios, Dolby and Sony and several others a couple years ago::
Quote:
Can video display or "emissive" monitors be used for Digital Cinema mastering?
Pines touched on the Stevens effect (that perceived contrast decreases at lower luminance), Hunt effect (that perceived colorfulness also decreases at lower luminance) and display flare characteristics.
Quote:
The same content has to look good in a normal surround (office), dim surround (living room) and dark surround (theatrical)
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People will disagree with me, but the way you do that is different display gammas, from 2.2 to 2.4 to 2.6 for each of the above.

Here is what Kevin Wines, Image Technology Director at THX said at the Symposium that I also found interesting:
Quote:
The viewing quality of video is dramatically affected by room lighting conditions. We have no control over what direction the windows face, and sunlight changes color and intensity throughout the day. Seldom is the light at that ideal level when we're finishing it in post production. No one is suggesting we change the standard for post production. But you do have to be ready to adjust playback for the environment. You may be better lowering the gamma to get the perception back, as opposed to less sophisticated behavior with adjusting brightness or contrast.


Previous post from last year, I think it's important to note that many projects are not graded only once for all distributions:
Of course, grading environments for film and those for projects intended for wide distribution (i.e. BD/DVD) will be different and color suites can tend to use lighting conditions more appropriate for projects to be seen under general living condition in normal homes. In fact, today's films go through many grading sessions depending on target dist. and even several just for Cinema...... blurb about Prometheus':

Stephen Nakamura, one of a handful of artists who helped to pioneer DI color grading, shares his experience on creating the look for Prometheus as envisioned by director Ridley Scott:
Quote:
My biggest challenge was maintain Ridley's vision throughout all these deliverables. We graded for different 3D projection systems, one that can put approximately both 4 foot-lamberts, the other 6 foot-lamberts, of light on the screen. We also mastered to 2D for digital cinema (a DCP version) and did another for film-out. We also had to create another one for IMAX, which has an entirely different aspect ratio. We also had to approve all IMAX prints, and there was IMAX digital and IMAX film. So that made for six versions of the film. Then of course there's the Blu-ray and DVD.

We started the workflow for grading the multiple 3D versions with the less-bright 4 foot-lambert version, grading that all the way through. Once that was done, then it's easy to do the 6 foot-lambert version; it's just about pushing more light through when projecting it onto the screen. Some shots that may be on the verge of being clipped, looking totally blown out, in 4 foot-lamberts won't look that way when projected at 6 foot-lamberts. Basically, anything that looks good projected at 4 foot-lamberts will generally look better projected at 6. It still requires some fine-tuning, but it certainly makes a lot more sense than grading for 6 first. So much of what looks good projected that way will look terrible at 4. We also based the 2D master on the 4 foot-lambert 3D master and made refinements for 2D's much brighter projection systems. For the IMAX version, the color remains the same, but it involves panning-and-scanning to accommodate the aspect ratio.

finding more, will edit
.
Edited by turbe - 12/21/13 at 1:18pm
post #575 of 636
Quote:
Originally Posted by turbe View Post

....
I found comments interesting from Josh Pines, Technicolor VP of Imaging Research & Development at the Hollywood Post Alliance first-ever Reference Monitor Symposium, sponsored by Walt Disney Studios, Dolby and Sony and several others a couple years ago::
Quote:
Can video display or "emissive" monitors be used for Digital Cinema mastering?
Pines touched on the Stevens effect (that perceived contrast decreases at lower luminance), Hunt effect (that perceived colorfulness also decreases at lower luminance) and display flare characteristics.
Quote:
The same content has to look good in a normal surround (office), dim surround (living room) and dark surround (theatrical)
Quote:
People will disagree with me, but the way you do that is different display gammas, from 2.2 to 2.4 to 2.6 for each of the above.
I have always understood this to be the case. Gamma has to be varied according to human perceptual limitations and characteristics. All of imaging science is based upon human vision. The fundamentals of delivering correct image reproduction must take into account how the eyes work and how the brain interprets what they register. When a standards body defines display alignment practice, the type of viewing conditions are either explicitly defined or reference is made to another practice document in the footnotes where environment conditions have been defined already.

Best regards and beautiful pictures,
G. Alan Brown, President
CinemaQuest, Inc.
A Lion AV Consultants affiliate

"Advancing the art and science of electronic imaging"
post #576 of 636
Quote:
Originally Posted by GeorgeAB View Post

Gamma has to be varied according to human perceptual limitations and characteristics. All of imaging science is based upon human vision. The fundamentals of delivering correct image reproduction must take into account how the eyes work and how the brain interprets what they register.

1000 x
post #577 of 636
There's going to be grading done with BT.1886 but it's not going to be like a switch is flipped and bam - every one is using it at that moment or required to.. It is a recommendation after all.

There's also a lot of content out there right now and a lot of projects

and different distributions
Quote:
Originally Posted by Stephen Nakamura 
Then of course there's the Blu-ray and DVD.

Edited by turbe - 12/21/13 at 1:58pm
post #578 of 636
So a night/day calibration should focus on gamma used, rather than lightoutput?
post #579 of 636
Quote:
Originally Posted by turbe View Post

There's going to be grading done with BT.1886 but it's not going to be like a switch is flipped and bam - every one is using it at that moment or required to.. It is a recommendation after all.

Rec 709 primaries are also a recommendation.
post #580 of 636
Quote:
Originally Posted by turbe View Post

There's going to be grading done with BT.1886 but it's not going to be like a switch is flipped and bam - every one is using it at that moment or required to.. It is a recommendation after all.

There's also a lot of content out there right now and a lot of projects

and different distributions

Yes it will be in transition to BT1886 for a couple of years. We are being told the studios did not want to switch mid season/series. So they start switching once this years series are wrapped up. You do know we work with Josh Pines and others at Technicolor directly and they switched to using CalMAN 5 at all Technicolor studios worldwide for a reason.
post #581 of 636
Quote:
Originally Posted by Wouter73 View Post

So a night/day calibration should focus on gamma used, rather than lightoutput?

possibly both.

If your eyes are adapted to a relatively bright surround lighting condition, you may need to have a higher peak luminance in order for the whites to pop out. But you may also need a lower gamma to compensate also.

My take on this is that it may actually be impossible to reproduce the perceptual image precisely if you are comparing different surround lighting conditions.

Which is why the principle of matching surround lighting (and color) conditions to that of the reference environment is taken very seriously by those who want a high fidelity experience.
post #582 of 636
Quote:
Originally Posted by derekjsmith View Post

Yes it will be in transition to BT1886 for a couple of years. We are being told the studios did not want to switch mid season/series. So they start switching once this years series are wrapped up. You do know we work with Josh Pines and others at Technicolor directly and they switched to using CalMAN 5 at all Technicolor studios worldwide for a reason.

I'd like see his comments again next year or after, it seems he indicated his same feelings this year as posted above from a couple years ago.

This is really two different things, whats being used in post and what's best at the viewing enviroment. There are also some (including at that Symposium) that will say it has been 2.35 (2.3) in post.

For viewing enviroment, I do believe along the lines of Josh's comment (and from Kevin's interesting comment again below) and I'll go so far to say that I also believe many if not most of the Professional Calibrators do as well.. at this time anyways.
Quote:
Originally Posted by Kevin Wines, Image Technology Director at THX 
But you do have to be ready to adjust playback for the environment.

Edited by turbe - 12/21/13 at 3:43pm
post #583 of 636
Quote:
Originally Posted by spacediver View Post



If your eyes are adapted to a relatively bright surround lighting condition, you may need to have a higher peak luminance in order for the whites to pop out. But you may also need a lower gamma to compensate also.

Many Professional Calibrators do this for their client's day setting.

I know the 30-40fL range is often given (I believe it's taught in both ISF and THX) for a fp in a reference enviroment, you may be surprised how many Calibrators have something less than 30fL (~24fL) for their own fp in a reference enviroment.
post #584 of 636
Quote:
Originally Posted by turbe View Post

Quote:
Originally Posted by spacediver View Post



If your eyes are adapted to a relatively bright surround lighting condition, you may need to have a higher peak luminance in order for the whites to pop out. But you may also need a lower gamma to compensate also.

Many Professional Calibrators do this for their client's day setting.

I know the 30-40fL range is often given (I believe it's taught in both ISF and THX) for a fp in a reference enviroment, you may be surprised how many Calibrators have something less than 30fL (~24fL) for their own fp in a reference enviroment.
Keep in mind that the ISF and THX are not the authorities. Those organizations simply have digested what imaging industry standards bodies have published as standards, engineering guidelines, and recommended practices, then composed classes formulated to teach the application of industry best practices for aligning display systems.

Joe Kane came out of the SMPTE Professional Monitor Working Group to teach, promote, and advocate for their revised findings in the late '80s. He partnered with Joel Silver to found the ISF, in order to further that mission.

George Lucas commissioned Tomlinson Holman to develop a structured program that could be used to help improve the consistency of quality in commercial cinemas. That became THX. The THX program was first a consulting and certification program for film image and sound mastering, as well as commercial cinema design and alignment. Since then, the organization has expanded into consumer audio and video. THX requirements are all based upon the assimilation and interpretation of the same type of standards bodies publications mentioned above.

The original SMPTE recommendation of 30 to 35 ftL peak white on a calibrated monitor was in the context of CRT linear operating limits, in a darkened/neutral colored viewing environment, with D65/10% of peak white ambient illumination (referred to as "dim surround"). That was defined as the reference for mastering monitor conditions at that time. This has persisted as pretty much the general pattern of practice ever since.
post #585 of 636
thanks for the historical insights George (btw I really enjoyed your home theatre geeks interview last month).
post #586 of 636
Quote:
Originally Posted by spacediver View Post

thanks for the historical insights George (btw I really enjoyed your home theatre geeks interview last month).
This link to the interview here at this forum may be a better resource for interested parties: http://www.avsforum.com/t/1499286/the-room-is-a-video-component-with-alan-brown#post_23953177 . It includes followup comments with subsequent links to available documents and other sources that focus on imaging science principles and/or display industry standards and best practices.

One of the improvements included in the 2nd edition of the 'S&M HD Benchmark' is test signals for adjusting ambient lighting (bias lighting) to better emulate reference viewing environment conditions. Unfortunately, not much discussion or instruction are included on the program or the associated web site to explain why these issues are important for display setup.

Joe Kane has provided more detail on this subject in all of his similar programs over the years. I have been an admirer of Stacey and Don's work over recent years and encouraged them to provide viewing environment setup materials when I discovered there would be a revised edition. Stacey responded favorably to the idea and asked for my input when they were designing the patterns for ambient light.

Any discussion of display system alignment fundamentals is incomplete without addressing human perceptual factors and viewing environment conditions. Reference imaging is only realized when reference display conditions are implemented. Any "benchmark" tutorial or guide for high definition viewing requirements ought to logically include human factors in the discussion. It's essential to understand video signals and the devices for conveying them, but it's just as essential to understand the human visual system and how viewing conditions can interfere with even the most perfectly aligned equipment.

Gamma relates to how a display translates a video signal. It also relates to how human visual adaptation perceives an image in specific viewing environment conditions. Reference viewing of video programs on television monitors assumes "dim surround" viewing conditions. Reference viewing of cinema programs on front projection systems assumes very dark or very near dark viewing conditions. So called "ISF Day Mode" for video displays is always a compromise due to interfering screen reflections, but also due to a different adapted visual state (different from reference).
post #587 of 636
Just a little confused as to how original fidelity can be maintained when we have so many variable conditions not only in the source and the viewing environment but also human perception..
post #588 of 636
Quote:
Originally Posted by PE06MCG View Post

Just a little confused as to how original fidelity can be maintained when we have so many variable conditions not only in the source and the viewing environment but also human perception..
It's simple. The viewer's best shot at fidelity is to implement best practices in video system design. That includes provisions for reference viewing conditions in the environment, which takes care of the perception issue. There's nothing a viewer can do about variations in the source except choose good sources (Blu-ray Disc instead of streaming/cable/satellite versions of a movie).

As the ISF classes have taught traditionally in the first session: television is not "plug-and-play," never has been, likely never will be. Confusion usually is caused by ignorance or wrong teaching. Viewers come to this section of the forum with all kinds of erroneous preconceptions they consider logically derived- unfortunately, from wrong information. The most "sensible" logical construction is worthless if based upon a false premise. One of the most common errors is that reference viewing can be realized in non-reference viewing conditions. Video displays can't overcome the laws of physics or human psycho/physiology.
Edited by GeorgeAB - 12/24/13 at 12:57pm
post #589 of 636
Quote:
Originally Posted by GeorgeAB View Post

It's simple. The viewer's best shot at fidelity is to implement best practices in video system design. That includes provisions for reference viewing conditions in the environment, which takes care of the perception issue. There's nothing a viewer can do about variations in the source except choose good sources (Blu-ray Disc instead of streaming/cable/satellite versions of a movie).

Thanks Alan,

Previous posts on this forum indicate variation / disagreement about Blu Ray mastered gamma.
post #590 of 636
Quote:
Originally Posted by PE06MCG View Post

Thanks Alan,

Previous posts on this forum indicate variation / disagreement about Blu Ray mastered gamma.

As Ted indicated, a good solution for now may be to have a number of different presets (e.g. 2.2, 2.4, BT.1886), and visually assess which one looks better (i.e. not too washed out, not too crushed).
post #591 of 636
Quote:
Originally Posted by PE06MCG View Post

Quote:
Originally Posted by GeorgeAB View Post

It's simple. The viewer's best shot at fidelity is to implement best practices in video system design. That includes provisions for reference viewing conditions in the environment, which takes care of the perception issue. There's nothing a viewer can do about variations in the source except choose good sources (Blu-ray Disc instead of streaming/cable/satellite versions of a movie).
....Previous posts on this forum indicate variation / disagreement about Blu Ray mastered gamma.
The program production/post/broadcast/duplication side of the video industry has never been in 100% unfailing agreement on best practices. No community ever has. There will always be debate and disagreement among "experts." That is one reason why the ISF and THX were formed- to serve as a translator/mediator on such issues. Disagreement is more tolerable if there is clarity in the debate. When there is clarity, the observer can choose which side to align with. As far as BD mastering gamma, there will be a dominant or prevailing practice among the mastering community. Imaging science practitioners and display system calibrators should be members of SMPTE in order to stay abreast of prevailing best practices, as well as in order to support their mission. From all that I've read, about 2.35 is probably the best compromise I would shoot for as consumer display gamma in "dim surround" viewing conditions, 2.2 for brighter conditions, and up to 2.6 for very dark front projection environments. There are more knowledgeable and more experienced contributors than I in this forum who may differ.
Edited by GeorgeAB - 12/22/13 at 3:26pm
post #592 of 636
Quote:
Originally Posted by spacediver View Post

As Ted indicated, a good solution for now may be to have a number of different presets (e.g. 2.2, 2.4, BT.1886), and visually assess which one looks better (i.e. not too washed out, not too crushed).

So control everything regarding the viewing environment regarding maintaining a constant low ambient light etc. then try out the Blu Ray at the various possibilities of gamma values.(after having calibrated each of these possibilities).
If more than one person viewing, get perception agreement then choose the one that looks correct from a majority vote.

Viewing may then be somewhere near optimum.

Well that seems to be simple, I'll give it a try.

Pardon my cynicism spacediver, but should it be that complicated?
post #593 of 636
Sorry, slightly OT, but in CalMAN 5, I know how to calibrate to 2.2 and 2.4, but how do I calibrate to BT.1886?
post #594 of 636
Stacey, Don or someone, I need some help.

I am testing whether passing HDMI through my HT controller has any noticeable effect on picture on my Mitsubishi DLP.

The only place I see a difference between a test signal straight from Oppo 103 and same signal routed through my AV controller is on the colorspace test.

Both upper pattern outside vertical stripe boxes ( magenta & blue stripes) appear much darker when going through the controller compared to direct out of the Oppo.

What's happening here? Much of an issue? Are high frequencies being clipped here? Can't notice a difference on conventional material.

I prefer to go through the controller for convernience ,but.....

Thanks much.
post #595 of 636
Quote:
Originally Posted by PE06MCG View Post

So control everything regarding the viewing environment regarding maintaining a constant low ambient light etc. then try out the Blu Ray at the various possibilities of gamma values.(after having calibrated each of these possibilities).
If more than one person viewing, get perception agreement then choose the one that looks correct from a majority vote.

Viewing may then be somewhere near optimum.

Well that seems to be simple, I'll give it a try.

Pardon my cynicism spacediver, but should it be that complicated?

Do you have a better solution? I think it's pretty clear that as far as we can tell, we have no direct way of knowing the EOTF during grading. Given that gap in knowledge, we can either choose to make an assumption, or we can test different hypotheses. Testing hypotheses takes time.

Controlling ambient environment should not be considered going above and beyond the call of duty.


It is a hassle, admittedly, to have different presets, but this is the price we pay for never having explicitly recommended a display end EOTF (until very recently with BT.1886).

And I don't think you really need more than one person to do the visual test, and it shouldn't take that long. If it's too dark or washed out, it should be obvious. Remember, the colorists aren't grading arbitrarily - they're aiming for a pleasing picture also.
post #596 of 636
Quote:
Originally Posted by spacediver View Post

As Ted indicated, a good solution for now may be to have a number of different presets (e.g. 2.2, 2.4, BT.1886), and visually assess which one looks better (i.e. not too washed out, not too crushed).

Note that technically it is pretty easy to use BT.1886 style black input offset with a non 2.4 power, allowing a simple "one number" adjustment for viewing conditions.

That's a far more precise spec. that "gamma 2.2, 2.4 ..." where the nature of the black point handling is unspecified, yet can have a huge impact on the result.
post #597 of 636
Quote:
Originally Posted by gwgill View Post

Note that technically it is pretty easy to use BT.1886 style black input offset with a non 2.4 power, allowing a simple "one number" adjustment for viewing conditions.

That's a far more precise spec. that "gamma 2.2, 2.4 ..." where the nature of the black point handling is unspecified, yet can have a huge impact on the result.

that's a good point. I imagine that this would be reserved for advanced users who can calculate their own target curves, unless the software explicitly had a setting for BT.1886 style with a custom exponent (as opposed to BT.1886 proper).
post #598 of 636
Quote:
Originally Posted by AustinJerry View Post

Sorry, slightly OT, but in CalMAN 5, I know how to calibrate to 2.2 and 2.4, but how do I calibrate to BT.1886?

It is an option in Calman just click on it same tab where you specify the gamma target,
post #599 of 636
Quote:
Originally Posted by spacediver View Post

Do you have a better solution? I think it's pretty clear that as far as we can tell, we have no direct way of knowing the EOTF during grading. Given that gap in knowledge, we can either choose to make an assumption, or we can test different hypotheses. Testing hypotheses takes time.

Controlling ambient environment should not be considered going above and beyond the call of duty.


It is a hassle, admittedly, to have different presets, but this is the price we pay for never having explicitly recommended a display end EOTF (until very recently with BT.1886).

And I don't think you really need more than one person to do the visual test, and it shouldn't take that long. If it's too dark or washed out, it should be obvious. Remember, the colorists aren't grading arbitrarily - they're aiming for a pleasing picture also.

Thanks for reply.

To answer bluntly no I do not have a better solution. My way is to even out the potential error by hoping that my choice of an EOTF of 2.4 (actually BT.1886).is midway between the probable possibilities of 2.2 to 2.6.

Perhaps my previous post was a trifle dismissive of at least a solution to the problem (apologies for that). I am so frustrated by the attempts of Calibration Experts generally to overcome the indifference of media producers to using a standard to master their products to. Well done to you all but in some instances perhaps the accuracy you try to reach cannot be achieved.

I know TV Channel viewing is contaminated with all sorts of compression, encryption and bit rate constraints but would the same technique be of value there?

Certainly until there is some sort of way to check the gamma of the Blu Rays we buy or they are manufactured to a known gamma standard then trying a range of gamma values is the only way forward.
Producing them is another chore requiring recalibration at the new values I presume?
Edited by PE06MCG - 12/23/13 at 10:54am
post #600 of 636
Quote:
Originally Posted by PE06MCG View Post

Certainly until there is some sort of way to check the gamma of the Blu Rays we buy or they are manufactured to a known gamma standard then trying a range of gamma values is the only way forward.
Producing them is another chore requiring recalibration at the new values I presume?

not in Lightspace. You profile the display only once. From that profile data you can then create different LUT's with Gamma of 2.2 | 2.3 | 2.4 | etc. - LUT creation takes maybe 5 secs. Store in different slots in your LUT box.

If you don't use 3D LUT's, I guess you would have to calibrate each input on your TV for a different target.
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