Likewise the colour management system and settings will be familiar to
those who previously used Photoshop 6 or 7. All of this is good news for
those migrating from earlier versions but colour management and
particularly the plethora of options associated with it can leave many
new users in a state of confusion.
This essay is primarily intended to help new Photoshop users and will
explain how the colour management system within Photoshop CS should be
configured. That said and before getting into the specifics I think it
worth taking a few moments reviewing the underlying principles of colour
management.
For ease of reading and to assist with quicker download of
screenshots, etc. I have broken the essay down into small sections. You
can easily access any section by clicking the appropriate link in the
Index shown below. I've also included a printer friendly version
(1.2MB) in the form of an Adobe Acrobat file. Click the following
Icon to download it
A Swedish language translation of this essay is
available from
Here
Ever since the beginning of colour reproduction, colour management has
existed in one form or another. The basic concept underlying colour
management is to ensure that colour data is processed in a consistent and
predictable way throughout the entire imaging workflow. A typical Imaging
System will consist a wide range of Input and Output Devices, and each
device will reproduce colour differently. This means that a colour
represented by one device will rarely if ever match the same colour
represented on another device. In other words, colour is
device-dependent. So expanding upon our earlier definition we can say
that the purpose of a Colour Management System (CMS) is to maintain the
consistent and accurate appearance of a colour on different devices (e.g.
scanners, monitors, printers, etc.) throughout our imaging workflow.
Components of a Colour Management System
In order that we can achieve the above aims a colour managed system
will require three basic components, namely: -
- A device-independent colour space - this is usually referred to as
the Working Space or Reference Colour Space.
- ICC/ColorSync device profiles for each device (printer, scanner,
monitor, digital camera, etc.) that describe the colour characteristics
of the specific device.
- A Colour Matching Module (CMM) that will interpret the information
contained within a device profile and carry out the instructions on the
way the colour gamut of each device should be treated.
The following diagram demonstrates a typical Colour Managed Workflow
and shows the image being passed along the chain - from scanner/digital
camera - to - computer - to - monitor - and printer with the ICC profiles
ensuring that the colour data from/to each device is correctly described.
Colour Numbers, their Meaning, and
Profiles
A digital image will comprise pixels each of which is represented by a
number. This number will describe the location of the pixel within the
image and its particular colour value (typically an RGB value). We have
already noted that since colour is device-dependent the appearance of the
each coloured pixel will vary for each device. We also noted that this is
because each device has its own unique way of translating the raw colour
value into visual colour. To minimise the discrepancies that result from
the widely differing colour characteristics of each device we use an ICC
profile to inform the CMM how the colour values produced by that device
should actually appear. This may be on our monitor, in print or on film
output. In simple terms it is the device profile that conveys the meaning
of the raw colour numbers associated with each pixel.
Whilst consumer class film and flatbed scanner software applications
are now ICC/ColorSync aware they tend to be based upon a colour space
known as sRGB, likewise consumer digital cameras. This colour space isnít
generally regarded as appropriate for high quality image editing,
especially when print or film output is required, but is quite often all
we can expect to get. An image delivered into Photoshop by the scanner or
digital camera application software which is already in a
device-independent colour space sRGB/Adobe RGB means that it has already
undergone a considerable amount of data processing and not that itís an
sRGB/Adobe RGB device.
Many Prosumer class scanners and digital printers are now supplied
with some form of generic or "canned" profiles. Whilst these profiles are
useable they are rarely accurate. For truly accurate colour matching you
should seriously consider getting customised profiles for each device
and/or media type. These profiles can be created professionally or by
buying your own profiling software. Sadly very few, if any digital camera
vendors have adopted the "canned" profile approach instead opting process
the images into a device-independent colour space as discussed above.
Device profiles come in two basic forms, i.e. Input and Output. Input
profiles typically describe the colour characteristics of scanners and
digital cameras, whereas Output profiles describe devices such as
monitors, printers and film recorders. Input profiles are often referred
to as one-way since it is only possible to select them as the Source
meaning we can never convert an image into the colour space of our
scanner or digital camera. Output profiles are two-way meaning we can
convert From or To them.
Why bother with Profiles?
Even though colour correction and colour management are not the same
thing they are often confused with each other, especially by the novice
Photoshop user. The colour characteristics of most imaging devices are
such that it is very rare for them to be truly linear (i.e.
R=G=B=Neutral). Sometimes this characteristic is referred to as the
device not being well behaved. Scanners and printers are good examples of
badly behaved devices. Obviously it would be extremely difficult for a
Photoshop user to edit an image where a group of pixels with values of
R=G=B=128 (grey) actually appeared to be non-neutral. In such
circumstances colour correction would an absolute nightmare. To overcome
these discrepancies we usually carry out all our editing in a colour
space that is well behaved. In Photoshop well behaved colour spaces are
more usually referred to as the Working Spaces, and are always
characterised by having R=G=B appearing neutral. Without the aid of
accurate device profiles the accurate translation of the raw colour data
(the numbers) from the scanner/digital camera into the Working Space will
prove very difficult, if not impossible. The translation from the Working
Space into the media specific colour space of a digital printer will
prove equally difficult without the aid of media specific printer
profiles.
So the main benefit offered by colour management is that the process
of colour correction can be undertaken in the knowledge that the image
displayed on the monitor is an accurate visual representation of the
original subject, and that the final print will accurately reflect the
colours of the displayed image.
Photoshop CS continues to use document/image specific colour settings,
which means that the colour space of each document is independent of
others that may be open on the Photoshop desktop. As with Photoshop 6 and
7 the Working Space defined in Color Settings only has a bearing on three
types of image, viz.: -
-
New images/documents.
-
Existing images/documents without an embedded ICC profile.
-
Images/documents with no embedded ICC/ColorSync profile (i.e. untagged
images/documents).
Image or document specific colour means that it's the profile embedded
within an image that determines how the image will be displayed (it's
appearance) and not the Photoshop Working Space. With Photoshop CS we can
have multiple images, each in its own unique Working Space, open at the
same time and each will be displayed accurately. Of course all of this
assumes we're using a calibrated monitor.
Note that except for the obvious difference in user interfaces;
Photoshop CS for Mac OSX and Windows share a virtually identical feature
set. Therefore the Windows based screen shots that follow should be
equally useful to Mac users.
On opening Photoshop CS for the very first time we are presented with
an information dialog (shown below). The purpose of this dialog is to
warn the user that the Photoshop Color Settings will be automatically
configured or to provide access for manual setup. As with Photoshop 6 and
7 there is no wizard to help the user through the process of
configuring the Color Settings. If Photoshop 6 and 7 are anything to go
by many new users will panic at this dialog and accept the defaults only
to realise later that this was only a short-term solution.
For the purpose of this essay I to have chosen the No option
and have therefore accepted the default Photoshop settings. However, I
chose this option for no other reason than to concentrate upon monitor
calibration and characterisation. Once I have discussed calibrating the
monitor we can return to Color Settings.
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