Re: Spectro question
Re: Spectro question
- Subject: Re: Spectro question
- From: "Stuart Peel" <email@hidden>
- Date: Tue, 3 Sep 2002 11:33:12 -0700
- Priority: normal
- Thread-topic: Spectro question
This is just a little input following on from Chris Murphy, just a
different way of explaining things.
On Monday, September 2, 2002, at 11:00 PM, "James B. Reswick, Jr."
writes:
>
>
My question is (finally): How can the profiling software know what
>
corrections to make when comparing only the CMYK text values
>
associated with
>
the target's patch and the measured Lab values for that patch, when
the
>
information contained in the target's CMYK text values are relative
>
percentages?
What I often find is that it is very easy for Colorsync users to drown
in the vast number of variables and technologies in the workflow. I
think what is important in controlling colour throughout the workflow
is; understanding and remembering basic fundamentals. This applies to
all aspects of colour reproduction including maintenance (calibration)
and Quality Assurance procedures (making sure you do the same thing time
after time).
ICC profiles simply describe what a 'Non-defective' observer sees in a
given lighting condition. When we take a reading of a particular colour
'Red' for instance, this is mapped into a mathematical model that
describes this colour 'Red' in 3D co-ordinates; Lab, XYZ etc. Now, if we
take our colour 'Red' from above and present it to a 'non-defective'
observer on a printed page (in controlled lighting conditions) with a
chart of the colours available in our mathematical model, our
'non-defective' observer would correctly identify the correct colour
from our chart.
What do we have from this? Well, we have a recipe that describes the
unique RGB or CMYK elements required to make this colour 'Red'.
Now to understand the recipe required to make our colour 'Red' on
another device we have to build an ICC profile specifically for that
device, which will then provide a means to establish the appropriate
RGB, CMYK or CMYK + OTHER COLOUR recipe. The map is from 'Device Colour
to Profile Connection Space Colour' and then 'Profile Connection Space
Colour to Device Colour'.
i.e. Device - Lab then Lab - Device
We can make this transformation using 'linked profiles' (which can be
utilised by only a few applications and RIP's) or by utilising a colour
server (which effectively link profiles and make colour transformations
from one device to another automatically) or we can utilise applications
such as Adobe Photoshop for making the transformations from one device
to another manually.
Anything in our workflow that can affect colour output must be
calibrated and incorproated into out quality assurance system. Our ICC
profiles simply describe what a given device produces in a given state
relative to what we see.
FWIW :-)
Stuart Peel
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