[scribus] Colour Profiles

[John Beardmore]

Hal V. Engel wrote:
> 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 
> specialized profiles. 

And LEDs will presumably be terrible !


>> 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. 

OK -  this seems more consistent with the observation that not all 
cameras give the same colour balance, brightness etc.


>> 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.

OK.


>> 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
>> corrections.
> 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.


>>> 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. 

Up to a point. The extent to which this is practical depends on the sort 
of work you do I guess.


>> 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. 

This presupposes that it's worth it and that there aren't simple 
approaches that achieve adequate results.


>> 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.

Are these widely available for laser toners or just inks ?


> 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
>> correctly?
>>
>> 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.

Except that in most domestic and non specialist small business settings, 
CMS will just be too much trouble.

I think this is something we need to recognise and be honest about.  The 
fact that almost anybody can afford it doesn't mean that the cost is 
justified, or that CMS would be more cost effective than having some 
manual control that you can use to set the desired curves for printing.


Cheers, J/.
-- 
John Beardmore, MSc EDM (Open), B.A. Chem (Oxon), CMIOSH, AIEMA, MEI
Managing Director, T4 Sustainability Limited. http://www.T4sLtd.co.uk/
Energy Audit, Carbon Management, Design Advice, Sustainable Energy
Consultancy and Installation, Carbon Trust Standard Registered Assessor
Phone: 0845 4561332   Mobile: 07785 563116   Skype: t4sustainability