Re: gamma bewilderment wrt/ Argyll’s documentation
Re: gamma bewilderment wrt/ Argyll’s documentation
- Subject: Re: gamma bewilderment wrt/ Argyll’s documentation
- From: Graeme Gill <email@hidden>
- Date: Fri, 01 Apr 2016 11:19:31 +1100
Uli Zappe wrote:
I happen to know a lot about it, but this knowledge is completely irrelevant here.
Saying so over and over again, doesn't make it so.
If ICC color management abstracts from a specific hardware, the hardware does not
matter, nor does its history. It’s as simple as that.
You are going to have a lot of trouble with your color management then.
Colorimetry != Appearance, and in practical terms, ICC profiles
are primarily Colorimetric characterizations.
where it says: “Historically, the default gamma correction for Mac OS has been a value
of 1.8 (a useful value for print professionals).”
Yep - they made the AppleWriter output match the Mac screen by tweaking the display
curve, and it landed at an overall gamma of 1.8 because that matches the dot gain of
the printer.
I wouldn't call it a "useful value for print professionals" though, since
different printers have different dot gains.
(i.e. whoever wrote the above quote doesn't actually understand the technicalities.)
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?
If you want to use a color management system at its most basic,
then maybe that will work for you. But if you want it to work better
than that, you have to understand more, and take more trouble.
In terms of device profiles, Colorimetery != Appearance. So
if you want to take appearance into account, you need to make
adjustments to the profiles ("configure") to allow for Appearance
effects, since by default profiles are based on Colorimetry.
And how profiles are actually used has plenty of
wrinkles if you want a good result, from gross things like
what intent/table you use, up to wanting actual gamut
mapping, conversion smoothness details, etc.
And what “expectations” are you talking about?
Expectations that images will appear as people expect them to appear.
Ooops!?! Maybe this is the core of my confusion and our disagreement?
What disagreement is that ? You just seem to have a particular axe to grind
about wanting to throw all backwards compatibility away and start afresh!
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?
Display calibration is a tool that helps both setup parameters that
an ICC profile can't conveniently manipulate (i.e. brightness, white point)
and makes the display better behaved at a detail level that something
like an cLUT profile can't conveniently manipulate. It also sets the tonal
response for non-color managed applications, which is something the vast
majority of people still have to deal with, because the vast majority of
software developers don't understand color, and don't want to.
Because sRGB like material dominates the world, conversion from/to
sRGB is important in meshing with a color managed workflows.
So yes, every open color management system has to "straddle"
the connection between sRGB and full color management.
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.
Really ? Where do you think it is stated that ArgyllCMS is an ICC and ICC only
color management system ? (hint - it doesn't). It primarily ICC based, yes, but
covers a lot of other stuff, including calibration of displays and printers,
spectral based aspects (i.e. observers, illuminants, FWA/OBE), Color Appearance, etc.
By your measure it seems that there are no ICC color profiling systems
in the world - all of them that deal with displays do display calibration
as a step before display profiling.
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.
You are quibbling about the implementation details. The overall effect is
similar, because it is for the same reason - an Appearance adjustment.
Putting it in gamma terms helps people who come from that background (i.e. Video)
understand the equivalence.
You keep saying that video is relevant for computers, without ever saying why, apart
from technical history.
The technical history is what we have to deal with (i.e. sRGB etc.).
Does that mean an engineer, let alone a passenger lives in the same world as a Roman
legionary? No, it doesn’t.
But it means if you wish to make a break from the past for the mere sake
of fashion, then you have a lot of work to do. How would you go about
eliminating all roads in Europe and replacing them with monorail track ?
What would be the date when that would happen ?
BT.1886 is a remainder from a pre-color management dark age when color reproduction
could only be adjusted by hardware calibration.
I'm glad you think that current color management has solved all color
problems, but I don't see that from where I stand.
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”.
I'm waiting then, for you to visit everyone in the world and deliver a "modern"
bright display, so that no-one making color management software has to
make any allowance for dim viewing conditions any more.
(hint - not everyone has the budget for the "latest and greatest", and some
technologies don't scale to high brightness economically, i.e. projectors.)
And this “considerable research” maintains that “contrast expansion is always
desirable”? :-O
Only if you say so, - I certainly don't.
You keep recommending me books as if I did not know what I’m talking about. I do. :-p
You haven't demonstrated that you do - quite the contrary.
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.
Then why do you keep saying it isn't ?
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*.
How do you know this ? Because your particular environment is bright, and
you think everyone should have new displays set to maximum brightness ?
Many print professionals deliberately calibrate their displays to a lower
brightness such as 100 cd/m^2 and adjust their surround accordingly, to match
various international standards, and the standards around sRGB that also assume
a not so bright viewing environment. These form an expectation about how
sRGB is to be interpreted from a color appearance point of view.
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.
Wow, you are so certain about how everyone else does things, aren't you ?
I guess there's no market for viewing booths, neutral paint or D50 lighting then ?
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.
If it doesn't match your situation, then disregard the information. How hard is that ?
(some brain power required!).
And if you merely wanted to suggest that I modify the documentation to make more
allowance for brighter, modern displays and viewing conditions, you've chosen a
strange and aggressive means of doing so.
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. ;-)
Every computer display you can buy defaults to emulating a CRT response.
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. :-)
Not the same as somehow changing all the sRGB like images and devices to some other,
non CRT derived colorspace standard though.
There is no “everything else” for me, for you there is.
For people who want to manage color and aren't you, there are
many different situations they'd like to be able to deal with.
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.
Things aren't so clean in the real world though. The ICC profile format
has tried to do that for colorimetric data, and doesn't work that well
in some situations (i.e. if you want to do real gamut mapping, high
quality conversions, etc.)
So for a computer, which is typically multi-tasking (i.e. multiple applications are
used), there is no alternative to this approach.
There are several viable approaches that make different tradeoffs of
convenience, quality and performance.
Graeme Gill.
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