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PART II - CHAPTER II
PHOTOSHOP 5 AND THE COLOR MANAGEMENT?
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Information
about Adobe Gamma
The
software Adobe Gamma is a utility for Macintosch and
PC. It is intended for the calibration and the characterization
of the monitor in a visual way. This intrument of adjustment
is not as powerful as the specific tools dedicated to
the color management and the creation of profiles of
screens. In all, the program makes it possible to gauge
contrast, luminosity, gamma, color balance and the white
point of the monitor. This is accompanied by the choice
of the type of phosphorus used in the monitor, i.e.
values for luminophores RGB. The adjustments can be
carried out by the control of the peripheral parameters
such as the ambient light and the time of pre-heating
of the monitor. This utility is installed at the time
of the installation of the software Adobe Photoshop.
The adjustment can be carried out step by step or in
a personalized way. It is however disadvised employing
this utility, because it is much less powerful than
a system of calibration
(measuring apparatus and its software).
The adjustments
of integrated colors (Edition/ Colors)
RGB Adjustment
The
color preference in Photoshop 6 has four adjustments
(RGB Adjustment, CMYK
Adjustment, gray level Adjustment, direct adjustment)
and are in a window entitled Workspaces. RGB Adjustment
has a certain number of choices which we will detail.
The preferences of RGB adjustment must be recorded in
the file which is in the system folder
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Figure 14: Personalized functions of the utility Adobe
Gamma
Figure 15: Window representing the adjustments colors
of Photoshop 6
Figure 16: Window representing the workspace RGB
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/ Support / Adobe/ Color/
Profile, contrary to the old version of Photoshop, where
the profiles were stored in the file Profils Colorsync
of the System folder. But Photoshop 6 also considers the
profiles stored in the folder Profil ColorSync .
The
calibration and the characterization of the monitor are
two essential stages before using Photoshop and its functionalities
related to the color management. This characterization
can be done with a tool for creation of screen profile
associated with a measuring instrument such as a colorimeter
(for example Kleo of Qubyx ).
The
first preference of RGB Adjustment relates to the choice
of the workspace. There is a choice of predefined spaces
in Photoshop 6, in which the four important ones are as
follows: APPLE RGB, Adobe RGB (1998), ColorMatch RGB,
and sRGB IEC61966-2.1. Nine spaces of reference present
in version 5 are found in Photoshop 6.
The
user can employ a space which is common with that of
the monitor of another user (calibration and characterization
with Kleo). Another function of the RGB adjustment is
that it gives free choice to the operator to make his
own adjustments..
Let us analyze briefly, the principal characteristics
of nine spaces of reference. |
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Space
RGB
This
color space became a standard for Hewlett-Packard and
Microsoft. It is intended for amateur applications and
the color management on Internet. Its gamut is rather
broad.
The characteristics of this space were clearly defined
by the creators, in particular which is related to the
conditions of observations to the screen and the parameters
of calibration. It is supposed to become the official
standard in terms of color space RGB. |
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Space
Apple RGB
This
space is based on a model of monitor 'APPLE Trinitron
13'. Its gamut is not as broad as that of sRGB. It is
used for the former versions of Photoshop, and for other
applications such as CAM of old generations.
For additional information,
it is advised to read the article entitled "A
standard default color space for the Internet-sRGB",
available on the Web to the following address:
http://www.color.org/sRGB.html |
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Space
ColorMatch RGB
It
is a space created by the Radius company, whose characteristics
are based on those of a monitor called PressView. Its
gamut is rather broad. This workspace is recommended to
utilize under Photoshop, by applying the parameters as
shown in the following figure. |
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Spaces
NTSC and CIE RGB
These are two obsolete spaces compared to those quoted
previously. Adobe Photoshop 6 guard in its RGB adjustments
with an aim of providing a rather important pallet of
adjustments. Their use is however increasingly reduced.
Space NTSC was conceived in 1953 by the National Television
Comittee Standards, and was presented in the form of
a standard for the color television sets. |
Figure 17: Window representing advised Adjustments RGB
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| Space
PAL/SECAM
It is a space intended for the color television sets
of present generation. This standard came into effect
only on the European continent, and some other countries
of the world (except USA).
Space
SMPTE-240
This space RGB is a space intended for the high definition
television production, and has a range of colors much
wider than the space intended for general public color
television. Space Adobe RGB (1998) is the equivalent
to the space SMPTE.
Space
SMPTE-C
It is a competitor for space RGB of the STAKESECAM
in Europe is used by the users of television sets NTSC. |
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Broad
space RGB Range
This space is also called as Wide Gamut RGB and it
is a very important space where certain colors could
not be reproduced in impression.
There is of course the possibility of using a definite
space RGB in a personalized way (cf appear preceding).
In this case, it is enough to regulate the value of
gamma, and to modify the values of the white point and
the primary colors (chromatic values of the luminophores
red, green and blue). |
CMYK
Adjustment
As
we can see it on the figure below, CMYK Adjustment has
a certain number of predefined choices on which we will
pay our attention.
Of course, we advise you to use profile CMYK
ICC, that is created with your system of profilisation
in Photoshop. On the other hand, if you do not have
a personalized profile and one of the generic profiles
is not appropriate to you, you have the possibility
of selecting your own adjustments in Photoshop. |
Figure 18: Window representing adjustments CMYK
Figure 19: Window representing the other options of CMYK
Adjustment
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| This
option is equivalent to the internal Adjustment of Photoshop
5. The choices are based on the Options of inking and
the Options of separation. These two preferences must
thus be carefully defined. It should be known that the
inks chosen by default in Photoshop 6, are inks SWOP
and art paper (cf preceding chapter describes this American
Standard).
Related to the choice to inks, it is first of all necessary
to choose in the drop-down menu on which standard you
want to work (Standard SWOP-USA, or Eurostandard-Europe).
From this choice, various options can be defined according
to the type of work to carry out.
Options
of inks
Colors
of inking
We
have the drop-down menu to specify a type of inking.
This one makes it possible to define precise values
of inking for a certain number of colors (C, M, Y, CY,
MY, K etc.). The below figure shows the configuration
of personalization of inks. The co-ordinates of these
values can be defined according to known spaces CIE
Yxy or CIE L*a*b*. The following figure shows this whole
parameters, which can be defined by the measurements
taken before using a spectrophotometer.
We
can thus choose co-ordinates between L*a*b * or Yxy,
estimation of the overprintings, different types of
épreuvage with
the screen, since it makes possible to visualize how
the values of |
Figure 20: Values of inking in CMYK Adjustment.
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selected inks behaves with
the impression (the épreuvage
is an essential stage that is explained in the next chapter).
Curves
of fattening
The
fattening can also be given in this window, maybe in a
standard way, or in the personalized way. In the case
of the standard fattening, the rate of four inkings is
always same. By personalizing, we can grant a specific
rate of fattening for each ink, as shown in the preceding
figure. It is essential to know the characteristics of
the test of control (measurements of the values of densites
using a densitometer by reflexion).
Option
of separation
By
superimposing inks yellow, magenta, cyan and black, we
can obtain an impression in quadrichromy. |
Figure 21: Option Curves fattening of Adjustment CMYK
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If an image is made up of
only the yellow, magenta and cyan or RGB, its total saturation
in impression will be weakened. This is why the black
makes it possible to increase the contrast of the image,
and to make more neutral the image (neutrality of the
gray).
The
internal parameters of the withdrawal of the under-colors
and the achromatic withdrawal can be defined at the time
of digitalization (pilot of the scanner), or maybe at
the time of conversion from RGB into CMYK at final improvement
of the image in software. The below example shows the
windows intended for the adjustments of parameters of
the UCR and the GCR. By defaut, Photoshop 6 uses the method
separation GCR.
Withdrawal
of under-colors (RCS or UCR)
The
withdrawal of under-colors RCS (UCR Under Color Removal)
makes it possible to use black for the replacement of
the primary colors in the gray shades and zones (neutral). |
Figure 22: Options of separation of Adjustment CMYK
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Achromatic
withdrawal or replacement of the gray
Achromatic
withdrawal GCR (Grey Component Replacement) makes it possible
to replace the gray component by a black equivalent, in
a well defined percentage. According to specificities
of the press used, it is possible to carry out adjustments
on the density of the black, on maximum inking, like the
addition of under-colors. The graph represented in the
dialog box Option of separation represents the scale of
the active gray of the white (0%) to the black (100%).
The value of inking for the reproduction of the gray is
represented on the vertical axis of the graph .
It
is also possible to do direct adjustments on the curve
of the black (option suitable for the software Adobe
Photoshop). In Photoshop, the average value of density
of the black is placed by default.
If
one selects the other option like Density of the black
from the drop-down menu, the curve of the black can
be handled manually, and it is shown in the opposite
curve. The maximum inking option present in the window
option of separation is usable with the methods of separation
GCR and UCR.
The option addition of under-color, has a considerable
role, since it makes possible to add colors in the zones
of low light, and after this the withdrawal of the black
is carried out by method GCR. Thus
makes it possible to obtain better results in these
zones of images and raises the total
colorimetric behaviour of the image. |
Figure 23: Options of separation and density of the black
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Addition
of cyan, magenta and yellow normally being used to produce
black. It proves that the association of these colors
gives the diluted black, but these zones were less clear
compared to the same ones printed with pure black ink.
Thus the images obtained have an insufficient dynamics
compared to the original image. The choice to substitute
black ink for cyan, magenta and yellow, have many advantages
which are described below.
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Figure 24: Graph representing the curve of the black
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Advantages
of these two methods
These
two methods have several considerable advantages. First
of all, it is necessary to know using of methods such
as the UCR and GCR. UCR makes it possible to gain in
contrast, especially on the level of the low lights.
GCR allows a reduction of the consumption of inks since
black ink replaces the three other yellow, magenta and
cyan on the whole of the image, and has the property
to balance the gray. The interference of the dyes between
them will reduce. The time of drying is also decreased
since there is nothing any more but only one layer of
ink (black) instead of three initially envisaged. This
last remark is obviously in relation to the print speed
which is thus increased, since the surface of bed for
inks yellow, magenta and cyan are not any more. As we
evoked previously, the images obtained are of better
quality, since clearer and more contrasted (in particular
in the shades).
At
which place does the conversion takes place?
The
separation of the colors, i.e. the conversion of a file
RGB into CMYK can be carried out at several places of
the graphic chain. According to the software of color
management, and the flow of production of the chain,
this conversion can prove to be more advantageous on
one level than the another. It is quite obvious that
the file on this same chain must be clearly defined
by the user before employing Color
Management System. The various parameters in
this operation are logical and functional type.
First
of all, this conversion can be carried out at the level
of the acquisition of the data (example the Silverfast
pilot of the Lynx scanners, Pro42 and Pro48 of Qubyx).
This software allows this conversion since it is compatible
ICC.
It
can be carried out at the time of the image processing
(Photoshop, X-Press, etc.), on the level of the RIP
of the printer, or on the server (ex: OPI). An O.P.I
is a system of exchange of files invented by the Aldus
company, and which is carried out between the files
in low resolution and the initial files, generally in
high resolution. This system of exchange is generally
associated a server, which is used to provide the page-setting
of the files for operators in weak resolution which
can be easily integrated in a composition. The handling
of the models is facilitated because of the weak
weight of the integrated files in the software
of page-setting. At the end of the handling, the assembly
of the composition makes it possible to substitute the
images in high resolution for the files in low resolution.
OPI Server must know to manage the connections with
RIPs PostScript (the concepts of RIP and Postscript
are described in the chapter devoted to the épreuvage).
Conversion
charts in Photoshop
It
is possible to change of the tables of separation which
was defined previously. Once the table is changed in
this module, its safeguard creates a ICC profile. The
latest version of photoshop 6 handles the loading of
tables resulting from former versions of Photoshop 6.
Photoshop 6 also have the choice of the application
priority for shaping ICC for the management of the colors.
The tables of separations contain information of each
peripheral present on the graphic chain. A profile ICC
is different from a table of separation, and it can
be converted besides into a table directly usable under
Photoshop. The software uses these tables to carry out
the conversion of a file located in a colorimetric
space towards another. The creation of a table
of separation can be carried out by a color management
system (CMS),
at the time of the phase of characterization of a peripheral,
for then being charged in Photoshop. Many still uses
this system of Tables of separation under Photoshop,
whereas others prefer to employ shaping ICC, who became
the current reference. Version 4 of Photoshop could
not manage profiles ICC, and this is why the use of
the tables colors proved to be essential.
Adjustment
Levels of gray in Photoshop
This
window presents two options which are related to the
behavior of the gray. The drop-down menu leaves the
choice through several preset adjustments and allows
us to apply the values of gamma and engraisemment different.
Shapping
ICC
Rules
of color management in Photoshop
It
is necessary to manage the various files between the
various operating systems and software applications
in an effective way . The configuration and adjustments
is to be carried out on the files of color profiles.
Thus, it is possible to configure the management of
ICC profile with its own way in Photoshop, at the time
of the file opening and recording.
The
choice of the type of profile is thus very important
and must be in correlation with the selected type of
exit.
Each
workspace (RGB, CMYK, Levels of gray) can be to handle
in three different ways. The choices are as follows:
Decontaminated, To preserve the incorporated profiles,
and Conversion (RGB, CMYK, Levels of gray).
We will approach in details specificities of these three
solutions.
The
first choice has several incidences. Indeed, new files,
as well as the existing files (i.e. those which are
already open under Photoshop 6) having a workspace other
than the workspace chosen in basic the Couleurs adjustment,
will not have any colorimetric description if this option
is selected.
The
second choice To preserve the built-in profiles makes
it possible to keep the profile of origin of the file
open under Photoshop. In the case of figure where a
file does not have profile ICC, this one will be seen
allotting at the time of its opening under Photoshop
6, workspace chosen in the adjustment basic Colors.
It will remain, however, with its closing, without profile
ICC, and it will change colorimetric description with
each opening under Photoshop, if the workspace is different.
The
third choice (Conversion of the workspace) is to be
taken with much more precaution.
Indeed, this option calls upon a conversion of the
data of the file, thus with a deterioration of those.
Options
of conversion
The Options of separation of the Couleurs window are
the same ones as those of the former version of Photoshop.
The type of CMM (Engine) and the type of calculation
(Mode) are to be determined. We approached the characteristics
of these two parameters in the chapter concerning profiles
ICC. The concept of Compensation of the black spot is
explained in framed opposite.
Compensation
of the Black spot
When
a file RGB is converted into a file CMYK, it may
be that the value of the black is not identical
in both cases. It is for that that the compensation
of the black spot must be activated. In Photoshop
6, this option is present, and makes it possible
the software éxaminer the types of selected
profiles ICC to evaluate the level of black in each
configuration. If the two black spots are different,
Photoshop 6 implements a system of compensation
so that the value of the black spot of the profile
source is correctly mapper in a value of black spot
of the profile of exit. In certain cases, this compensation
gives bad results, however it should be known that
in the majority of the cases of transformation of
a file RGB into CMYK, or of a file CMYK in another
file CMYK, the compensation of the black spot is
carried out under good conditions. In the case of
an exit RGB, the compensation of the black spot
must be handled with precaution. As in the two preceding
cases, to pass from a file RGB to another RGB, while
clicking on the Compensation option of the black
spot will give good results. However, it may be
that the impression has diluted blacks. The test
is thus best solutions in this case of figure. In
the case of a numerical épreuvage for a standard
impression
newsprint (or the blacks are not very dense), it
is recommended not to use this option.
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Option
To convert into profile
With
regard to the conversion of a colorimetric mode into
another mode, the software Adobe Photoshop 6 follows
a course which is clean for him since it passes by an
intermediary in Lab mode. From this file of transition,
the file can be converted in any other colorimetric
mode (CMYK, RGB, etc.). When you decide to convert a
file RGB into CMYK, Photoshop uses the indications specified
in the dialog box Réglage RGB (standard of profile,
gamma, not white, and primary educations), and conversion
in space CIELAB.
carries out. The second conversion is thus that busy
of the CIELAB with the CMYK. To finish, Photoshop carries
out a last conversion to return in RGB (necessary for
the visualization of file CMYK on the monitor). This
last operation can appear paradoxical, but it should
be known that it is carried out on a copy of the file
définitf CMYK.
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Figure 25: Option To convert into profile
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Option
To allot a profile
This
option makes it possible to modify a file by changing
profile color, without deteriorating the data of this
one. This action is different from a file conversion,
but its finality is the same bus we obtain a change of
returned (reversible) of the original file. In the case
of figure where we would like to test returned of an image
on another type of exit that that for which the file is
profiled, this option of attribution of profile is the
operation to be carried out. The Aperçu function
Attribuer window a profile makes it possible to visualize
the résulat instantaneously change of profile. |
Figure 24: Option To allot a profile
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Incorporation
of profiles
This
option is available at the time of enregisrement of a
file (cf appear below). It is necessary however that this
recording is carried out in a format supporting the ICC.
It is the case for formats EPS,
JPEG, PICT, DCS, Pdf, PSD, and tiff. At the time of the
recording, we can choose the option Utiliser the format
of test (format pdf, EPS, DCS1.0 and DCS 2.0). |
Figure 25: Functions To record Under and Incorporation
of profile
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Function
Format of test
This
function is comparable with a épreuvage screen.
We will see in the chapter according to the design features
and economic of this type of épreuvage. In its
principle, this function makes it possible to obtain directly
with the screen an outline colors of the printer file
on an unspecified peripheral. It is enough to choose the
space of profile of test to be simulated. The choices
are varied since we can choose a personalized épreuvage
(choice of a colorimetric profile of a particular peripheral),
that is to say a preset workspace (CMYK, Cyan, Magenta,
Yellow), that is to say to simulate returned the RGB of
such or such type of monitor. It
is possible to simulate the blank paper, what causes
to be able to visualize with the screen the specific
colour of the support of impression. Moreover, broken
Noir simulation relates to that of black ink and is
in direct correlation with the dynamics covered by such
or such type of inking. |
Figure 26: Function Format of test
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| - PART
II - CHAPTER II - PHOTOSHOP 5 AND THE COLOR MANAGEMENT
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© 2001-2003 Qubyx LTD All rights
reserved |
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