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Re: Color Managed View - How?

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Hal V. Engel

Re: Color Managed View - How?

> Am Friday 24 August 2007 schrieb Paul Waldo:
> > Gerhard Kulzer wrote:
> > > Am Thursday 23 August 2007 schrieb Paul Waldo:
> > >> Hi all,
> > >>
> > >> I was reading through the Digikam docs relating to ICC and came across
> > >> this surprising sentence:
> > >>
> > >> "The Use color managed view is an alternative to using Xcalib or
> >> > Argyll.
> > >> Only your image will be color managed, not your entire screen!"
> > >>
> > >> How does Digikam do this? I would think it would need to know how the
> > >> monitor behaves in order to render the colors properly...
> > >>
> > >> Paul
> > >
> > > You are correct, in order to color-manage, digiKam needs to have a
> > > monitor profile.
> > >
> > > Gerhard
> >
> > Yes, and monitor profiles are created by programs like Xcalib and
> > Argyll, aren't they? I'm confused as to how profiling applications can
> > be taken out of the loop....
> >
> > Paul
>
> Xcalib and Argyll are programs that apply a color profile to X, so all
> programs are automatically color-managed as far as the monitor is concerned
> (that means that the monitor is somewhat more neutral in its color
> rendering,
> missing color lobes can't be displayed of course, and notebooks are terribly
> bad when it come to photographs, no whatever sophisticated color management
> can correct that).
>
> Xcalib and Argyll don't manage other devices than screens. So they are
> partial color managers.
>
> Gerhard

Paul and Gerhard,

After looking at the answers that Paul received to his question I concluded
that there was a significant amount of misinformation in those replies. As a
result I joined this email list in the hope that I could clear up some of
these misconceptions. Let me start off with a very quick overview.

Color managing a display or monitor is divided into two parts but only one of
these is really the color management part. One of these is called
calibration and the other is called characterization. Characterization is
the part that is really color management.

This is a confusing point for most new users of color management in that they
tend to think that color management is about calibration. This, of course,
is not the case. Calibration is a process where a device it brought into
some defined state by making adjustments to it's controls or some other
physical means. For example, the act of calibrating a monitor involves
adjusting its white point, black level, luminosity and gamma to predetermined
or standard values using the monitors controls and by altering the video card
gamma ramp.

In many cases software for profiling monitors, like LProf or the set of
utilities in ArgyllCMS, also have the ability to calibrate displays as part
of the profiling process and this is another reason that this is confusing to
many users. The main point is that these are different and that you as a
user of color management need to have at least a basic understanding of the
difference. Note that calibration affects everything that is displayed (well
almost since Xv video playback by passes the video card gamma tables in many
current x11 drivers) not just applications that are color management aware
like Digikam or Krita.

In contrast to calibration the process of creating a profile is a
characterization of the device that does not involve making any changes or
adjustments to the device. Rather it is a measurement process that results
in a file that contains a precise mathematical description of the devices
color and tonality characteristics. This file is an ICC profile. These
characteristics include the transfer function from the devices color space to
a standardized absolute color space (this is called a Profile Color Space,
PCS, in an ICC profile), the devices white point, black point, primaries and
other information. Displays are normally characterized (profiled) in their
calibrated state.

To summarize calibration makes changes to the device to alter it's color
reproduction characteristics to conform to some predetermined state.
Profiling or characterization is a measurement process that results in a
detailed description of the device's (normally calibrated) color reproduction
characteristics.

In ArgyllCMS dispcal is used to calibrate the display, dispread is used to
create a set of measurements that are used to create a profile (IE. to
characterize the display) and profile is used to create a profile using the
files created by dispcal and dispread. In LProf these functions are
combined into a single GUI wizard rather than being separate programs.

ArgyllCMS also includes a program named dispwin that can read either an ICC
profile that contains gamma table calibration data (called a VCGT tag) or use
the file created by dispcal directly to apply the calibration to the video
card gamma table. This is also what xcalib does only xcalib can only use an
ICC profile with a VCGT tag. LProf does not contain a gamma loader and it's
users are encouraged to use either xcalib or dispwin.

The point here is that you can characterize (IE. profile) your display in
either a calibrated or uncalibrated state and you can use the resulting
profiles in any color management aware application. The main differences are
that if you calibrate your display before profiling all of your applications
benefit, even those that are not color management aware, and the adjustments
being made as a result of using the display profile in a CM aware application
will be somewhat better because the color space transform will be making
smaller adjustments to the image as it is displayed.

Based on this I am not sure why Digikam would need to have some setting
specifically for this. In addition, even the sentence from the Digikam
docs "The Use color managed view is an alternative to using Xcalib or Argyll.
Only your image will be color managed, not your entire screen!" seems to
contain some misinformation since with current implementations of x11,
Windows and OS/X the most that you can achieve for the whole display is that
the display is well calibrated but not color managed. None of these systems
do color management of the whole display and only color management aware
software running on these systems can give you color managed results.

Also just for clarity xcalib is a video card gamma table loader and it does
not have any functionality for creating profiles or for doing the actual
calibration (IE. measurements, adjustments and gamma table creation). In
addition, ArgyllCMS is actually a complete CM solution. It allows you to
profile scanners, displays and printers if you have the proper equipment. It
is however a set of command line utilities and is not very user friendly.

I hope this helped.

Hal
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Arnd Baecker

Re: Color Managed View - How?

Hi Hal,

thanks a lot for this very helpful overview!

So far I have not started using color management, because
I don't have a device for profiling my screen.
Unfortunately, it seems that there are not many
which work under linux. For example the spyder hack
http://www.yan-ke.com/spyder/
to support ColorVisions Spyder colorimeter
did not make any progress in the last months.
(And the DTP94 Optix listed at
http://www.argyllcms.com/doc/ArgyllDoc.html
is difficult to get and not that cheap)

But maybe this is not really necessary and
setting the monitor to sRGB (as I can do on my Eizo)
and adjust gamma with lprof
(http://sourceforge.net/project/screenshots.php?group_id=146038&ssid=21740)
is already better than nothing?

Still I think that to ease the use of color management
in the context of digikam there should be a brief list of steps
(like a recipe ;-) which one should follow to get
everything setup properly.
The handbook already provides a description of the concepts,
http://docs.kde.org/development/en/extragear-graphics/digikam/using-iccprofile.html
but I am looking more for something like
1) set screen to sRGB
2) adjust gamma and brightness of the screen properly
3) enable color management and use the right ICC profile for you camera
4) do all manipulation in a "large" color space
(e.g. ProPhoto RGB ?,
http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml)
4) (?) use the right output profile for your printer or one provided by
the lab to print your images (of course you need a good lab for this)

Note the previous points are in complete ignorance of how
it should be done correctly!

While all the concepts behind color-management and color spaces
are not trivial, somehow I have the feeling that
it still should be simple to use in the end
(presumably it is already, but I haven't grasped it yet ... ;-)

Best, Arnd

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Bugzilla from thorsten.schnebeck@gmx.net

Re: Color Managed View - How?

Am Samstag 01 September 2007 schrieb Arnd Baecker:

> Hi Hal,
>
> thanks a lot for this very helpful overview!
>
> So far I have not started using color management, because
> I don't have a device for profiling my screen.
> Unfortunately, it seems that there are not many
> which work under linux. For example the spyder hack
> http://www.yan-ke.com/spyder/
> to support ColorVisions Spyder colorimeter
> did not make any progress in the last months.
> (And the DTP94 Optix listed at
> http://www.argyllcms.com/doc/ArgyllDoc.html
> is difficult to get and not that cheap)

I have the information, that there will be a Linux Verion for the Spyder in
late fall. Here is the original message:

> Hallo Herr Schnebeck,
>
> Wir haben eine funktionierende Optical Version für Linux, aber sind dabei
> alle unsere produke neu aufzulegen (hardware und software) - und möchten
> daher im augenblick mit der "alten" version nicht auf dem markt. Die neue
> Spyderlinie werden wir ab spätherbst auch in einen linux-variante anbieten
> (auch weil wir einen aktiven grosskunden haben, der auf linux-plattform
> arbeitet)
>
> Besten Gruss aus Zürich,
>
> Christoph Gamper
>
> -------------------------
> Datacolor AG,
> ColorVision Business Unit
> Christoph Gamper,
> General Manager EMEA

Bye

Thorsten
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Arnd Baecker

Re: Color Managed View - How?

Hi Thorsten,

On Sat, 1 Sep 2007, Thorsten Schnebeck wrote:

[...]

> I have the information, that there will be a Linux Verion for the Spyder in
> late fall. Here is the original message:

This is great news (my attempts to contact the company in this respect
failed ... ;-) - thanks a lot for the information!

Best,

Arnd
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Hal V. Engel

Re: Color Managed View - How?

In reply to this post by Arnd Baecker

Arnd,

Some very good questions. I will try to provide some answers in line.

On Saturday 01 September 2007 04:57:47 Arnd Baecker wrote:

LProf CVS now supports the EyeOne Display line (original, 2 and LT) as well a
the EyeOne Pro meters. It also supports a number of older discontinued
meters like the DTP94, DTP92 and Spectrolino. EyeOne Display LTs are fairly
inexpensive at least in the US with street prices in the $120 to $130 range
which also includes Windows and Mac calibration and profiling software -
which you can't use on your Linux workstation. This is still not "cheap"
but DTP94's were seeling for $199 with no software when they were
discontinued and only two years ago these were closer to $300. The ArgyllCMS
0.70 beta releases also support these meters.

I also have an OEM agreement with X-Rite for the EyeOne meters and if there
were sufficient interest I might be able to sell these at a slightly lower
price then the normal street prices. But I have to order these in larger
quantities, I can't order just 2 or 5 units, so this means I would need firm
commitments for enough buyers to cover an order from the vendor.

>
> But maybe this is not really necessary and
> setting the monitor to sRGB (as I can do on my Eizo)
> and adjust gamma with lprof
> (http://sourceforge.net/project/screenshots.php?group_id=146038&ssid=21740)
> is already better than nothing?

Yes better than nothing but you will be surprised at how much better your
results are if you do a measurement based calibration and profiling of your
display. The LProf rough profiler gamma screen uses the Norman Koren gamma
chart (with permission) and allows you to "measure" the gamma of the
individual display channels. This visual gamma chart is the best one
available and is much better than those used in other products such as
AdobeGamma. Monica also uses this gamma chart.

>
> Still I think that to ease the use of color management
> in the context of digikam there should be a brief list of steps

If only it were that simple.

> (like a recipe ;-) which one should follow to get
> everything setup properly.
> The handbook already provides a description of the concepts,
> http://docs.kde.org/development/en/extragear-graphics/digikam/using-iccprof
>ile.html but I am looking more for something like
> 1) set screen to sRGB

Only some displays have a setting for this type of thing - most will not.

> 2) adjust gamma and brightness of the screen properly

How do you do this without a measurement device?

Actually if your display allows you to adjust the gamma curves of the
individual channels (most do not but the Eizo display may) then you could use
the LProf rough profiler gamma screen to adjust this. It will not be as
close as using a measurement device and it will not correct for
non-linearities but you should be able to get the overall gamma within 0.1 of
your target value.

A typical measurement based calibration will get the gamma of the three
channels to with in 0.03 of your target and will also correct for non-linear
display response. It also allows you to precisely set the white point,
luminosity (brightness control on an LCD and contrast control on a CRT),
black point (if the display supports this adjustment - most do not) and black
level (brightness control on a CRT). I do not know of any way to do these
setting accurately without a meter.

> 3) enable color management and use the right ICC profile for you camera

With LProf or ArgyllCMS and an IT8 target you can create your own custom
camera and scanner profiles. LProf documentation has a tutorial on how to do
this for use in UFRAW. You should be able it extrapolate this for use with
other RAW work flows. LProf CVS now supports other targets including the
ColorChecker series and Hutch Color targets which were added as part of the
Google Summer of Code project. Some of this code (ColorChecker DC and SG
support) went in just last night and I have not been able to review it yet
and it is mostly untested at this point.

> 4) do all manipulation in a "large" color space
> (e.g. ProPhoto RGB ?,
> http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml)

IMO ProPhotoRGB, at about 94% of Lab space, is too large and it must be used
with great care. It should not be used for 8 bit/channel workflows ever. In
fact you should avoid 8 bit/channel workflows in general no matter what color
space you are using. A better choice would be something like BetaRGB (69% of
Lab space) which is designed to be large enough for almost any photographic
content but is shaped in such a way that almost all of it's gamut is usable
(much of the ProPhotoRGB gamut is not even visible to humans). Stay away
from sRGB (35% of Lab space) and only use it for web output, emails and
things like that (consider it an output only profile). In addition AdobeRGB
(50% of Lab space) is also somewhat on the small side but is better than sRGB
as an editing color space.

> 4) (?) use the right output profile for your printer or one provided by
> the lab to print your images (of course you need a good lab for this)

Many labs now know how to handle CM work flows even some fairly inexpensive
ones. As an example Costco, a large US "big box" chain store, publishes the
profiles for their printers on-line for each store (IE. these are custom
profiles). Costco has garnered a good reputation both for the high quality
of prints created using these profiles and the low cost of the service. This
is just one example and there are likely other low cost printing services
available that provide ICC profiles for their printers or color management
work flow information for their service.

Profiling your own printers is more of an issue. For Windows and Mac many
paper vendors will supply free paper/printer specific profiles that are
almost as good as custom profiles. But this is not the case for other
platforms such as Linux and you can not use a profile intended for use on a
Mac or Windows. This means we must create our own profiles or go to a
profiling service. The equipment to create printer profiles is not cheap
starting at about $650. Fortunately there are a number of services that will
produce custom printer profiles for around $25 and for most inkjet printers
this only needs to be done one time for each paper you use for the life of
the printer. One example is located here

http://www.blackfiveservices.co.uk/profiling.shtml

So this is not expensive.

>
> Note the previous points are in complete ignorance of how
> it should be done correctly!
>
> While all the concepts behind color-management and color spaces
> are not trivial, somehow I have the feeling that
> it still should be simple to use in the end
> (presumably it is already, but I haven't grasped it yet ... ;-)

Unfortunately Color management is one of those things that is not trivial to
setup or to understand. There is a significant learning curve but in return
for getting past that learning curve you end up with a very powerful tool
that allows you to get consistently better results with less effort. Because
of the steep learning curve many photographers give up before they get far
enough along to leverage the tools it provides. There are more resources
than ever available that can help you in your quest to learn about and use
color management and the tools to support it - software, meters and targets -
are becoming better and lower in cost.

The most important thing to keep in mind is that to get the best results you
need profiles for YOUR devices and YOUR work flow. Even devices of the same
make and model will have sample to sample variation and a profile that I
created for my camera might not give the same results for your camera of the
same model because of this. On the other hand it might be "close enough" for
your camera if your work flow is the same as mine. But things like different
setting during RAW conversion or using a different RAW conversion program
would make the profile invalid even for the same device. So a consistant
imaging work flow is critical. Software like ArgyllCMS and LProf along with
the supported meters and targets give you the tools you need to create these
profiles without having to spend a furtune.

Hal

PS: Digikam apparently uses some of the LProf code base. For what exactly I
am not sure but it appears to use some of the profile checker functionality.
See http://sourceforge.net/project/screenshots.php?group_id=146038&ssid=21739
for a screen shot.
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Arnd Baecker

Re: Color Managed View - How?

Hi,

just a brief update (on this pretty old thread ;-) concerning
hardware support for colorvisions spyder:
http://www.yan-ke.com/spyder/
"""
Protocol Decoded
September 28th, 2007

I have been busy for the past couple of months so I haven\u2019t been able
to work on this project. However, Graeme Gill sent me some code today that
properly communicates with the Spyder. Thanks Graeme! Attached is his code
which he wrote for Argyll, released under GNU GPL v3. Most of the heavy
work is done, and the next step is simply packaging it into a
\u201clibspyder\u201d. """

http://yan-ke.com/spyder/wp-content/uploads/2007/09/spyd2.zip

Best, Arnd
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Arnd Baecker

Re: Color Managed View - How?

In reply to this post by Arnd Baecker

Hi,

this is a followup to an oldish thread, but still...

On Sat, 1 Sep 2007, Arnd Baecker wrote:

> Hi Thorsten,
>
> On Sat, 1 Sep 2007, Thorsten Schnebeck wrote:
>
> [...]
>
> > I have the information, that there will be a Linux Verion for the Spyder in
> > late fall. Here is the original message:
>
> This is great news (my attempts to contact the company in this respect
> failed ... ;-) - thanks a lot for the information!

Unfortunately, it seems that there won't be a linux version
for the spyder, as the companies policy forbids
to cooperate with "OpenSource solutions"
http://lists.freedesktop.org/archives/openicc/2007q4/001026.html

So to me the message is very clear:
"Do not buy ColorVision products"
(if you intend to use the stuff under linux...)

In the (longer) thread, the Huey is discussed to be the
most interesting alternative (its support is in ArgyllCMS V0.70 Beta 7
and LProf/CVS and thus very recent).
((What is not clear to me is whether the
"Pantone huey Pro" makes a difference to the "Pantone huey Pro"
when used under linux ...))

Best, Arnd

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