[scribus] Colour Profiles
Hal V. Engel
hvengel at astound.net
Sun Sep 6 21:46:50 CEST 2009
On Sunday 06 September 2009 07:03:03 am Peter Nermander wrote:
> > So are we saying that for every digital camera that ships, the
> > manufacturer should provide a profile which we should select with
> > Scribus ? If so, what file extension are we looking for ? I'm not
> > aware of having one, but happy to look. What if we use pictures from
> > multiple cameras ? Would we not then need to apply a profile per picture
> > ?
> The problem is that the profile for a camera would depend on the
> ambient light when you take the photo.
This is true to a certain extent but it is both simpler and more complex.
Digital cameras can have white points set for different types of light sources
for in camera processing (this also applies to raw processing but it happens
later in the process) and this corrects the images to about a 5000K white
point. This is sort of like using different types of slide film under different
lighting conditions for those old enough to have worked with slide film. For
light sources with a smooth light spectrum you can use a single profile since
the images coming out of the camera or the RAW processing have all been
corrected to the same white point and will have nearly the same gamma
characteristics. But for light sources with spikes or drop outs in the
spectra you will likely need to create specialized profiles since there will be
an interaction between the spectral characteristics of the light source and
the sensor. In general sun light, sky light, strobe, flash bulbs and all
incandescent lights have smooth spectra. So this covers the vast majority of
light sources you are likely to use. On the other hand most florescent lights
have large spikes and dropouts in the spectra and will likely require
> But you don't need a profile for the camera, since the camera
> manufacturer put the profile into the camera.
But what profile is that? How do you know what profile to tag the images with
so that downstream processing (like printing or viewing on a monitor) knows
what the characteristics of the device that produced the image are? Remember
that any time you need to view or print something that the color management
engine needs two profiles to do this correctly. A source and a destination
profile. So I disagree - you do need a camera profile. I think your assertion
is that it is possible to use some "standard" or generic profile.
> The pictures from the
> camera will be in a "standard" colorspace like sRGB or for better
> cameras maybe AdobeRGB.
Perhaps but perhaps this is mostly wishful thinking.
> Of course the professionals only shoot RAW, and then apply corrections
> to get what they want, but they will still save the resulting image
> (usually a TIFF) using AdobeRGB.
They do? I know that this is not how I do my RAW processing. I create custom
profiles for my cameras for my RAW processing work flow. I then use these
custom profiles as part of that work flow to convert from the cameras native
color space to my standard working color space. This is both easy to do and
very powerful. The only thing that is needed is a profiling target of some
sort and a little effort.
> You could say that when you use RAW
> you create the profile for each picture while you apply the
You do? I know that this is not how I handle it. When using a good custom
profile I seldom make any adjustments to the photo during RAW processing other
than to make exposure adjustments.
> > OK - but again, the paper and ink issues alone make this implausible
> > for those of us that aren't professional printers.
> Not really. The profile is valid for each combinaton of paper and ink.
and driver and driver settings. For this to really work you need to have a
very controlled, consistent and repeatable work flow. The main thing is to
select what your work flow(s) will look like (IE. paper, ink, driver settings
...) and then always do it exactly the same way. Of course even if you are
not using color management you should still have a consistent work flow.
> As long as you buy the same ink and use the same paper the colors will
> not differ much.
Again you need to have tight controls on your printing work flow. Everything
must be the same for every print job. Consistency is the key. This is
something that the professional print shops do. They have institutionalized
highly consistent work flows so that they get consistent results. There is no
reason that end users can't do the same thing in their home or office "print
shop". They just need to think through what they are doing and then remove
variations in their processes.
> And there are companies that create a profile from a
> printed testsheet you send them. You download a file from their
> homepage, print it, send the print by mail to them and get a profile
> back. Not sure of the cost though, but a lot less than buying your own
> equipment to do the calibration.
This is basically correct. These services used to be expensive (like $100 to
$200 per profile) but in the last 5 or so years there has been a lot of new
service providers entering the market. In addition the cost of the equipment
has come down significantly and these factors have driven down the cost. Now
days it is not hard to find services that will do RGB printer profiles for $25
and CMYK profiles for $35. This makes getting good printer profiles well with
in reach for almost anyone. It is also a good idea for Windows and OS/X users
to check with their paper/ink vendor to see if free high quality profiles are
available. In many cases they are and if your paper/ink vendor does not
supply these then perhaps you should consider switching media vendors.
And a clarification profiling is NOT a calibration process it is a
characterization process. That is the profile describes the devices color and
tonal characteristics. Calibration is an adjustment to do the the device or
it's driver that changes it's characteristics.
> If you want top quality you should make a new profile each time you
> change ink and each time you open a new pack of paper. But you
> probably don't need to make a new profile that often if you stick to
> the same ink and paper.
Basically I agree but to a certain extent this depends on what equipment you
are using and how picky you are. For example Epson ink jet printers have a
high level of consistency and changing inks is less of an issue than the
differences between having new (fuller) ink cartridges vs. ones with lower
levels of ink and ink levels are a very minor issue. But HP ink jet printers
since the print head is built into the cart will have more variation from cart
to cart since you are also getting new print heads every time you change inks.
But in most cases with ink jet printers as long as you use the same ink vendor
and the same paper (vendor and type) and the same driver settings you should
be fine with one profile for the life of the device.
> > What I'd like is a means of colour management that may well sacrifice
> > some accuracy, but is quick to use, and can be used with any printer,
> > but gives acceptable results at a cost, and for an amount of effort,
> > that is appropriate to the size and requirements of small jobs that
> > don't need perfect colour, but would benefit from colour that isn't
> > totally uncorrected.
> You have an image, where the printout does not match what you see on
> screen. May I ask why you don't go the easy route and adjust your
> screen so it matches the printer output? Then you can adjust the image
> on you screen until it looks as you want it, and it will print
> Becuase your result might be because your monitor is not correctly
> adjusted. If it is a matter of dark/light pictures, an incorrectly set
> gamma is the most likely cause. Creating a simple profile with gamma
> adjustments is quite easy. Look at for example lprof.
LProf will allow you to create a profile that has the gamma correctly
characterized and also has some aids for setting the black level. But if your
display has inflections in the gamma curves (uncommon for CTRs but fairly
common on LCDs) you will still have issues (IE. LProf assumes that your gamma
curves are smooth and this may not always be true).
Back when this was first put into LProf (around 1999) the equipment needed to
do measurement based calibration and profiling of monitors was fairly expensive
at around $400 for the least costly devices not including software. Now days
you can get measurement devices like the X-Rite Huey for around $50 plus
shipping including basic calibration/profiling software. The Huey is a better
device than the $400 device was a decade ago since it will hold it's
calibration better. The older device would require re-calibration about
every 2 years. In other words the hardware is both cheaper and better now
days than it has ever been. There is no reason that anyone who is concerned
about color should not have one.
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