Re: gamma bewilderment wrt/ Argyll’s documentation
Re: gamma bewilderment wrt/ Argyll’s documentation
- Subject: Re: gamma bewilderment wrt/ Argyll’s documentation
- From: Andreas Kraushaar <email@hidden>
- Date: Thu, 31 Mar 2016 18:50:28 +0200
Dear all,
my experience about this:
"you reap what you sow” - as simple as that. There is enough information on how to get excellent colour accuracy. People are mostly happy with good enough quality (not colour accuracy but brilliant colours).
We provide a lot of free information (http://www.fogra.org/en/fogra-research/prepress/research-projects-prepress/softproof-2-625/downloads-2-626/downloads-for-softproof.html <http://www.fogra.org/en/fogra-research/prepress/research-projects-prepress/softproof-2-625/downloads-2-626/downloads-for-softproof.html>) and the demand is very limited.
regards
Andy Kraushaar
Our quality, neutrality
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Dr.-Ing. Andreas Kraushaar
Dept. Prepress
Fogra Graphic Technology Research Association
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> On 31 Mar 2016, at 18:30, Uli Zappe <email@hidden> wrote:
>
> Am 31.03.2016 um 08:31 schrieb Graeme Gill <email@hidden>:
>
>>> Why you are talking about television here? Conceptually, a computer has nothing to do with television.
>> Hmm. Do you really not know anything about the development of computers and electronic display technology ?
>
> I happen to know a lot about it, but this knowledge is completely irrelevant here.
>
> If ICC color management abstracts from a specific hardware, the hardware does not matter, nor does its history. It’s as simple as that.
>
> And *conceptually*, the technological implementation is even more irrelevant. From a conceptual POV, a television set is a low-end mass entertainment device, whereas a computer is a (possibly high-end) specialist tool. Not a single assumption about TV usage can be transferred to assumptions about computer usage. For instance, all this “dim environment” stuff is irrelevant for computer usage.
>
>> For continuity/backwards compatibility and the above technical signal encoding reasons, new display technologies are generally made to be backwards compatible with the CRT EOTF.
>
> This may or may not be the case. Again: It’s irrelevant for a color managed computer, because the ICC monitor profile abstracts from the specifics of the display, be it backwards compatible or not.
>
>> I'm not sure why you are so certain you understand the basis for Apples choice
>
> It has been documented countless times by Apple itself and Apple historians. I already linked https://developer.apple.com/library/mac/releasenotes/MacOSX/WhatsNewInOSX/Articles/MacOSX10_6.html where it says: “Historically, the default gamma correction for Mac OS has been a value of 1.8 (a useful value for print professionals).”
>
> Also, see Tom Lianza’s comments in “: gamma bewilderment: A history lesson”.
>
>>> In short:
>>> 1. In ICC color management, the display gamma is completely irrelevant in principle (= assuming no limitations in bit depth), because changing it will not change the image display at all.
>> Yes. But then I'm not talking about the physical display gamma in that context, but the target response of the display under color management.
>
> Which again is nothing the user needs to care about. It’s the job of the CMM to match whatever source to this target response. If color management works, changing the target response will (in principle) have no visible effect whatsoever.
>
>> Discussing the idealized device responses of (say) the TV system sets the stage for understanding how to configure a color management system to comply with the expectations and standards of image encoding and display.
>
> Sorry, I have no idea what you are talking about here. What does it mean to “configure a color management system” other than making sure that your visual content is tagged correctly and your input and output devices use the correct ICC profiles? You certainly need not know anything about the technical background to do that. Or do you talk about a developer’s POV here?
>
> And what “expectations” are you talking about?
>
>> (That and the fact that fully color managed applications are more the exception than the rule, and everything else assumed sRGB.)
>
> Ooops!?! Maybe this is the core of my confusion and our disagreement?
>
> I’m using OS X exclusively since 2000. Which means that outside of video, I have not used a single non-color managed application for 16 years now. Since 2009, when Apple introduced ICC video color management, this includes video and is true for 100% of the applications I use.
>
> So clearly, a non-color managed application is a thing of the ancient past from my POV. For you, it seems to be still relevant.
>
> So is your approach (here and in the Argyll doc) some kind of straddle which tries to achieve a desired color reproduction for both color managed and non-color managed applications at the same time?
>
> If so, this doesn’t become clear in the Argyll doc, at least for somebody like me who uses a 100% color managed computer. I mean, if I’m reading the documentation of ICC color management software, I do not expect configuration settings that are meant for non-color managed applications.
>
>>> 2. In ICC color management, it isn’t even possible/makes sense to “use a system gamma 2.2 with a gamma 2.4 monitor”. Whatever monitor gamma you have, you’ll have a monitor profile with the same gamma, and every differing gamma will be matched to that.
>> Well, of course it is. If the display profile is setup expecting sRGB encoding and viewing conditions, and the perceptual table of the profile is setup for the display under dim viewing conditions, then an appearance transform will have a quite similar effect to a gamma adjustment of around 1.1. - 1.2.
>
> It will have a similar *effect*, yes. But “using a system gamma 2.2 with a gamma 2.4 monitor” it is *not*. This is simply impossible with (a correctly configured) ICC color management.
>
>>> I read this of course, but again, it has little to do with computers.
>> Course ? Book!
>
> ???
>
>> Yes, it has a lot of relevance to computers.
>
> You keep saying that video is relevant for computers, without ever saying why, apart from technical history.
>
>>> Pointon comes from the video world, which is a very different world.
>> Except for the fact that computer displays trace their history and standard back to the video world.
>
> So what? Why do you care?
>
> The track gauge of European railways stems from the wheelbase of the chariots of the Roman Empire.
>
> Does that mean an engineer, let alone a passenger lives in the same world as a Roman legionary? No, it doesn’t.
>
>>>> BT.1886 is also pertinent.
>>> Certainly not.
>> Certainly is, since it is a standardization of the CRT display characteristic that underlies computer display standards.
>
> ICC color management works great with displays which comply with BT.1886. It also works great with displays which do not comply with BT.1886. So where is the importance of BT.1886?
>
> BT.1886 is a remainder from a pre-color management dark age when color reproduction could only be adjusted by hardware calibration.
>
>> If you have a 50 cd/m^2 CRT on a computer,
>
> 50 cd/m^2? CRT? Are you sure you live in the 21st century?
>
>> Of course ifyou have a 350 cd/m^2 LCD display, you can use it in a much brighter environment,
>
> Exactly. And it need not even be 350 cd/m^2. Even the cheapest displays offer 200 cd/m^2 nowadays, which roughly correlates an illuminance of 700 lx, *brighter* than the 500 lx ICC v4 assumes for “actual home and office viewing environments”.
>
> Which means that if anything, the color appearance adjustment would have to be for a *bright* environment, not a dim one.
>
> If the environment is not quite as bright as the display, 500 lx seems a reasonable assumption. Which means that typically, *no* appearance adjustment is required at all.
>
>> and the setup for viewing standard images will be slightly different.
>
> “slightly different”? Nope. Very different, in that simply no appearance adjustment is required.
>
>>> Well, if even 1.961 still counts as “approximately 2.2”, then almost any gamma curve will be “approximately 2.2”. ;-) Gamma curves outside of the 2.2 ± 0.3 range are probably quite rare.
>> CRT's are typically 2.4-2.5, which is distinct from 2.0-2.2.
>
> 2.4-2.5 is no more distinct from 2.2 than 1.961 ...
>
>>> ? Where is the “law of color appearance” that says “contrast expansion is always desirable”?
>> There has been considerable research into color appearance, much of it embodied in CIECAM02 and the associated scientific papers.
>
> And this “considerable research” maintains that “contrast expansion is always desirable”? :-O
>
>> Mark Fairchild's book is a good introduction.
>
> You keep recommending me books as if I did not know what I’m talking about. I do. :-p
>
>> As noted, a contrast expansion is desirable when adjust for the difference between a bright viewing environment and a dim viewing environment.
>
> For the umpteenth time: I do know that a contrast expansion is desirable *when* adjusting for the difference between a bright viewing environment and a dim viewing environment.
>
> That is not the point.
>
> The point is that computers are typically used in a bright viewing environment and therefore an adjustment for the difference between a bright viewing environment and a dim viewing environment is *neither required nor appropriate*.
>
>>> A contrast expansion is desirable if and only if the viewing environment is dimmer than the production environment. This is typically not the case with computers.
>> It was very typical
>
> No, it was never typical for computers. Because with a computer, the working environment is typically the viewing environment at the same time. I create a page layout in the very same environment in which I watch it.
>
>> Having been given an understanding of what and why an appearance adjustment may be desirable, you can now figure out how to allow for that.
>
> Now? I could even do that before, thank you. And because I figured out long ago that I need no appearance adjustment for my computer, I’m puzzled by the Argyll doc which keeps saying that I do.
>
>> Those who cannot remember the past are condemned to repeat it,
>
> While this is true in many cases, thankfully it’s not true for CRTs:
>
> Even if I can and do not remember the time when CRTs were used as computer monitors, chances are minuscule that – as a consequence – I’ll be condemned to use a CRT monitor for my computer in the future. ;-)
>
>>> I’m well aware of the *history* of *television* color processing.
>> You aren't showing it.
>
> Yep, because I’m convinced it’s irrelevant.
>
>>> What I don’t understand is why *computer* users should care about that *today*.
>> If you have some magic wand that can suddenly switch everyone system to a new standard overnight, I'm sure there are many companies that would like to buy it off you.
>
> The magic wand is called Mac OS X, and has switched to a new, 100% color managed system 16 (7 for video) years ago. :-)
>
>>> But this is history now. Today you can color manage video just as you have been able to color manage still images for the last 20 years. So whatever historical standards existed, you can emulate in a corresponding video profile which “virtualises” the historic video hardware, so to speak.
>> Yes. So what
>
> “So what”??? =:-O So that: This means that all your musings about hardware history are superfluous.
>
>> - that's exactly what ArgyllCMS and other color management systems achieve.
>
> YES! But then, why do you still care about the old way?
>
>>> There shouldn’t be any non-color managed output anymore in 2016 ... oh well ...
>> I'm not sure what dream world you live in,
>
> OS X :-)
>
>> but the vast majority of systems and software are color managed only by the expectation that everything is sRGB. Apple systems are amongst the best in terms of pervasive color management, but its still not in everything
>
> I’m not aware of anything Apple in OS X that isn’t color managed. A few very bad behaving third party applications (typically cross-platform) do not use color management, but nobody is forced to use any of them.
>
>> and not in any hand-held device.
>
> True. But I won’t use my iPhone for color critical work.
>
>>> But if you agree that these are the two reasons for calibrating a display for an ICC color managed computer, aren’t you saying yourself that appearance adjustments (i.e. contrast adjustments via gamma settings) are *not* among the reasons for a specific calibration?
>> Not for color managed applications no, but certainly for everything else.
>
> OK, so that’s the core point.
>
> There is no “everything else” for me, for you there is.
>
> The confusion in the Argyll doc, then, would come from the situation that it seems so clear to you that you talk about not only color management, but also about correct color reproduction for non-color managed applications, that you do not point this out very explicitly; whereas someone like me expects ICC color management stuff only and becomes confused when this content is mixed with non-color management content.
>
>>> I think the monitor profile is the only logical place to perform any output appearance adjustments, because color appearance phenomena happen at the screen → observer stage.
>> Yes and no. It's a practical location to do it, but like color management itself, there is both a source and a destination which together determine the overall transform needed. You can try and cut it into two peices with a common appearance space as an intermediary
>
> And this is in fact the *only* possible approach if you care about color consistency among multiple color-managed applications that you use. There has to be a common reference point.
>
> So for a computer, which is typically multi-tasking (i.e. multiple applications are used), there is no alternative to this approach.
>
>> (which ICC PCS attempts to do to some degree), so you can mix and match source and destination profiles, but this may not always give you a good result, or be practical.
>
> I’m well aware of the current limitations of this approach. ;-|
>
>>> If I send my images into the wild tagged with an ICC profile, effectively I’ll send my image in a device independent color space (the PCS).
>> Colorimetry != Color Appearance.
>
> True, but any color appearance adjustments are the job of those in the wild – what do I know about their viewing environments?
>
> Bye
> Uli
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