Toast analogy -- was: Re[2]: Dummy profile
Toast analogy -- was: Re[2]: Dummy profile
- Subject: Toast analogy -- was: Re[2]: Dummy profile
- From: Peter Karp <email@hidden>
- Date: Mon, 16 Feb 2004 11:07:22 +0100
Roger Breton schrieb am 13.02.2004:
>
You know the famous toaster analogy from Steve, how dark you like your
>
toasts and the idea of color management?
No, it seems he does not know the analogy...
----------------------- insert Toast here -------------------------
by Steve Upton of Chromix
A lot has been written and said about color management in an attempt to
describe what it is, what it solves and how it works. Like any discussion
about computing, these descriptions often use fancy new terms that
effectively confuse and turn off people who just want to understand,
well, what it is, what it solves and how it works.
An effective and greatly simplified analogy is that of the toaster. Pay
attention here because this is one even your clients will understand.
Let's say you get up in the morning, walk out to your kitchen and place a
piece of bread in your toaster setting it to a level of "4". After a
little while a certain color of toast pops out - hopefully a pleasing
color. Now if you take the next piece of bread in the loaf over to your
neighbors and put it in his toaster at the same setting of "4" do you
think you will get the same color of toast?
Probably not.
This is the problem of color management. The settings used on the toaster
do not necessarily produce the same colors. As in the toaster, RGB and
CMYK values on your computer are also just settings. And, just like the
toasters, when they are sent to different devices, they produce different
colors!
Now if you were a severe toast geek, you would toast 10 pieces of bread
in your toaster; one at every setting. Then you would lay them all out in
order on your kitchen table, grab the bag of bread and head over to your
neighbor's. Avoiding his bewildered stares you would toast 10 pieces of
bread in his toaster and take them back to lay on your table beside your
toaster's work. Fanning through your Pantone independent toast guide(*)
you would decide that "B" was, in fact, the color of toast you prefer.
Looking up and down your toaster column you would confirm that yes,
indeed, "4" is the setting on your toaster that will get you the color
you want - you know this after several mornings of frantically waving
smoke away from the alarm on your kitchen ceiling. After looking over
your neighbor's toaster column, you note that a setting of "6" is what is
needed to get the color you want from his toaster.
This, in essence, is what color management is all about. Carefully
sampling what a device (monitor, printer, toaster, whatever) will do and
then comparing it to an independent guide for actual color. In the case
of the toast we used the fictitious Toast Guide and in the case of
computers we typically use the Lab color space. Lab is a whole 3D range
of numbers across 3 coordinates (L for lightness and a & b for color
information). The important thing about Lab is that it is actually COLOR.
That is, a number that represents a sensation.
Let's take a little reminder on color. Color is a sensation produced by
the cooperation of our eyes and our brains in response to mixtures of
light. To have color you need 1) light, 2) an object and 3) an observer -
for our purposes, a human observer. Without all these components you do
not have color.
Lab, as mentioned, is a whole range of numbers that are assigned to
actual sensations. Each Lab number - like 50, 23, 47 - describes what a
certain sample will look like under 5000K lighting (a graphic arts
viewing standard in use in most viewing booths) and from a standard
distance (creating a specifically sized spot on the retina) to an
"average" person. In 1931 a group of scientists sat over 200 people down
to perform painstaking color tests to come up with this "average" person
and for our purposes it works quite well.
Back to the toaster.
To get the same color from different toasters, we needed to sample all
the colors of toast the lowly machine could produce and then compare them
to an independent guide. This lookup table is the equivalent of an ICC
profile.
To get the same color from different devices - what we are basically
trying to do here - we need to sample all the colors that device can
produce and setup a table that converts between the device settings -
say, a monitor - and the colors it produces at those settings. For a
monitor we attach a device to the monitor and then run software that
walks through a list of settings,: red (255,0,0), yellow (255,255,0),
green (0,255,0), and so forth. At each RGB value, it takes a reading with
the instrument and gets a Lab color back. After running through a long
list that only a computer should have to suffer, a profile is built for
that monitor.
If we want to get the same color from our printer as well then we also
need to build a profile for it. The same technique applies. We send a
file out to the printer that contains a long list of settings - for
example: cyan (100,0,0,0), blue (100,100,0,0), magenta (0,100,0,0), and
so forth. We then read each patch on the paper with a device like the
Eye-One that supplies Lab values for each corresponding set of CMYK
settings that were sent. A few calculations and your computer produces a
profile for your printer.
Great, you think, but how do I use these things? That depends on what you
are trying to achieve.
A good example is when you want to get the file you print to match the
one you see on screen. The file on screen is, by definition, in
MonitorRGB and you need to convert it to PrinterCMYK. If you apply the
monitor profile to the file, it will convert all those MonitorRGB
settings which are unique to your monitor to Lab (remember the toaster).
Lab, you will recall, is color - so we are out of the arbitrary world of
settings that only work for your monitor and on to something much more
useful.
Any profile can be applied to those Lab values to get the color you want.
In this case, we want the color to go to your printer. When the printer
profile is applied it formulates the correct CMYK settings for each color
in your file. A good quality profile will do a great job of matching
those colors within the abilities of the printer.
------------------------- Toast ejected ---------------------------------
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