[Scribus] How do I do color correction

[Hal V. Engel]

On Tuesday 06 March 2007 10:11, Dwain Alford wrote:
> i have been mystified by color management for years.  all of this profiling
> for different papers, inks, printers.  well at last i have come upon a
> system that works for me and it didn't cost any money profiling any
> hardware of for paper.
>
> most non postscript printers render i rgb, regardless of how many ink
> cartridges you have to install.  all of this monitor calibration i have
> found is bunk as well.  and as for paper, well, i use what ever i want and
> still get a good print with the expected results of ink absorption with
> certain papers and the finish of the paper (read: photo).
>
> i have an epson stylus photo 1200.  it has a black cartridge and a 6 color
> color cartridge. 

The 1200 series has 6 inks total including the black cart not seven.  Probably 
a typo.

> i have fought with getting what is on the screen to the 
> paper since i have had it, but i finally figured it out.
>
> now i am on a windows os, so your installed profiles may be different, but
> i do believe that the srgb color space (same as srgb iec61966-2.1) is
> available on all operating systems.  one other note, kodak and hp offer a
> srgb iec61966-2.1.  in fact, on my system, the srgb color space profile is
> from hp and the srgb profile is from kodak to be used in a d65 monitor set
> up with a gama of roughly 1.8.

sRGB is an approximation of a monitor calibrated to gamma 2.2 and D65.  Not 
gamma 1.8 which is a now long obsolete Mac standard.  In addition, most CRTs 
have a native gamma between 2.3 and 2.5 so even sRGB will be incorrect for 
most CRTs.

>
> when available i set my graphics software (all of them) to srgb
> iec61966-2.1for the rgb color space.  i use the swop v2 setting for
> cmyk (this setting
> depends on the color profile of your commercial printer, match it and
> you're in heaven, nirvana, elysian fields or any other good place you want
> to be). inkscape uses a flavor of srgb iec61999-2.1.
>
> now for the hardware.  i set my printer to the srgb color space profile.

As you point out above you are on Windows.  On Windows the system default 
color space is sRGB and all devices (printer, video...) using the default 
driver settings are supposed to be sRGB.  This of course is not always the 
case (in fact it seldom is) and users who understand color management do not 
use the default driver settings for printing in their color managed work 
flows.  Why? Because in the default mode the drivers do all sorts of 
automatic stuff that make them unsuited to a color managed work flow.  That 
is the results are unpredictable unless all of the automatic trickery is 
turned off.  

If you go to the Epson download site you can get a set of profiles for many of 
the Epson printers including the 1280/1290, R2400, R1800, R800.....  I don't 
know about the 1200 but you might want to check.   In addition there is a 
manual that is part of the download that describes how to use these profiles.  
That manual says to use the no color correction mode (IE. turn off all of the 
automatic stuff) when using the supplied profiles.  In addition the manual 
has very detailed instructions on all of the settings to be used in the 
driver with the profiles.  These profiles are paper and printer specific and 
are only valid with the specific Epson papers used to create the profiles.  
These are Epson's directions on how to make color management work with their 
printers not mine.  So please have a look.

One other thing to point out is that even though modern ink jet printers like 
the Epson 1280 and R2400 have a limited somewhat smallish gamut the gamuts of 
these devices have a significantly different shape than the sRGB gamut and 
there is are significant parts of the gamuts of these devices that fall 
outside of what can be represented by sRGB (yellows are the worst case).  
That is you will be getting either clipping of what would otherwise be usable 
colors or you will be incorrectly printing some colors if you treat these 
devices as sRGB devices.    The gamuts of these printers are also 
significantly larger than your typical offset printer so profiles like 
ISOCoated are not correct for these devices either. 

> now you can go to http://www.color.org and down load icc profiles.  there
> you will find the srgb profile mentioned above one with and one without
> black point settings.  read the difference between the two.  i have used
> them both, but for the hardware i have i stick with the srgb color space
> profile.
>
> my microtek 5900 scanner is set to srgb iec6199-2.1

Why?  It is easy and inexpensive to create custom profiles for your scanners 
and cameras.  For flat bed scanners all you need is an ($15 + shipping)  
IT8.7/2 target from Wolf Faust, LProf or ArgyllCMS (Lprof is easier to use 
and both are open source and free), and a few minutes to scan the IT8/7.2 
target and process it into a high quality custom profile.  Both pieces of 
software will create world class input device profiles.  If correctly created 
these custom profiles will definitely be better than using sRGB for your 
scanner.  As an example raw processed images from my DSLR have a gamut that 
is almost twice as large as sRGB at almost 70% of CIELab.  There is no way 
that I could use sRGB for this device and not either loose (clip) or 
misrepresent almost half of the devices available gamut.  I should also point 
out that the IT8.7/2 target itself actually has a gamut that is larger than 
the sRGB gamut and most scanners will be able to capture the full gamut of 
the target.

> and so is my monitor, 
> but the colors are sometimes off, what to do, what to do?
>
> here comes the tricky part, the monitor settings.  i have seen them all.
> some go to yellow side (d50) and some go to the blue (d93); but as for me,
> i want a neutral setup.  i took the chance one day and did the user
> settings to adjust my monitor.
>
> now i come from a photographic background and understand a little about
> color and color correction.  since i wanted a neutral setup that would
> render a print as close to what i had on my monitor i had to make my
> monitor neutral, thus the need for the user defined color settings.
>
> i took a deep breath and set the r,g & b to 50%, and made a print.  now
> remember all of my software and hardware carry the same srgb and cmyk color
> profiles.  when i viewed the print, it was like a miracle, but it didn't
> match my monitor.  the print was lighter than my monitor.  i saw all of the
> detail and color that i was supposed to, the brightness and contrast in the
> print was where i wanted it, but it didn't match my monitor.  so i turned
> up the brightness on my monitor to match, as closely as possible, the
> density of the print.
>
> viola!  i was in synch hardware and software wise for the first time since
> 1999.  but did it really work outside my environment?  i write a basic
> computer skill column for a local weekly newspaper.  i sent them a black
> and white print.  looked like it did on my monitor.  but what about color? 
> i had done some business graphics for my nephew's business.  we made his
> business card and had it printed, from a pdf (although not a scribus pdf)
> and the colors came out like on my monitor.

OK you think your monitor is now correctly calibrated but is it really?  Since 
you are a Windows user (same is true for Mac users) you can shop around and 
purchase a Pantone Huey for about $50 + shipping (look on ebay).  This device 
and the included software will allow you to calibrate and custom profile your 
monitor(s).  I think you will be surprised at how much better all of this 
works with a hardware calibrated and profiled monitor.   I know that I 
thought that my visually calibrated monitors were pretty close but I was 
shocked at how much better they were after using a hardware measurement 
device to calibrate and profile my monitors. For Windows and Mac users the 
cost of getting the hardware and software to do this is now so low that there 
is absolutely no reason for any Windows or Mac user who is doing color 
critical work to not have this type of device and software. 

One other point about hardware calibration.  Even with this hardware and 
software to guide setting the monitor controls I can get the white point to 
be very good with a delta E of less than 1.0 (very small error level) 
relative to D65 but at that setting my black point is off by a delta E of 
about 16 (large error level).  Which means that my average delta E along the 
black locus (the neutral tones) is about a 7 or 8.  At that point the monitor 
is more neutral than I have ever been able to achieve using visual 
techniques.  Then running a hardware based calibration and loading the video 
LUT with the resulting data corrects the black point problems and results in 
an improved average delta E of around 1.0 with a peak of about 3.0.  In 
addition the display gamma goes from 2.53 before LUT loading to 2.24 (nearly 
perfect) after the LUT is loaded.   Overall the amount of improvement in the 
display calibration and neutrality is striking.  Having used both visual and 
hardware techniques for this I can tell you that with the low cost of getting 
the hardware and software these days that I can no longer recommend using 
visual techniques to anyone who is doing color critical work.

When I do color critical work on Windows I use profiles provided by my paper 
vendor for my printer.  In my case this is the Illford Galleria Smooth Gloss 
paper profile for the Epson R2400.  The results are very good and even more 
important totally predictable.  It might be possible to get slightly better 
results with a custom printer profile since like all mechanical devices these 
printers do have sample to sample variation.  In addition when I send images 
out to printing services that have good color management work flows the 
results I get back are an excellent match to what comes out of my Epson 
printer and to what I see on my display. 

So for Windows and Mac users you can get setup to do input device (scanners 
and cameras) profiling and hardware based monitor calibration and profiling 
for less than $100.  You can also get free profiles from most paper vendors 
for most currently produced color printers.  This will allow you to setup an 
end to end color managed work flow that will give you consistent totally 
predicable results.

Hal