Difference between revisions of "GIMP/CMYK support"

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(Added a link to gimp-plugin-separate in AUR)
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{{Article summary start}}
 
{{Article summary start}}
{{Article summary text|This article will show how to enable rudimentary CMYK support in The GIMP using the Separate plug-in, and explain how to use color proof filter to soft-proof your images. It will also cover more general topics on CMYK colors and DTP.}}
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{{Article summary text|This article will show how to enable rudimentary CMYK support in Gimp using the Separate and Separate+ plug-ins, and explain how to use color proof filter to soft-proof your images. It will also cover more general topics on CMYK colors and DTP.}}
 
{{Article summary heading|Available languages}}
 
{{Article summary heading|Available languages}}
 
{{I18n entry|English|CMYK support in The GIMP}}
 
{{I18n entry|English|CMYK support in The GIMP}}
 
{{Article summary heading|Required software}}
 
{{Article summary heading|Required software}}
{{Article summary link|The GIMP (v2.0 and above)|http://www.gimp.org/}}
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{{Article summary link|Gimp (v2.0 and above)|http://www.gimp.org/}}
{{Article summary link|lcms (v1.15 ?)|http://www.littlecms.com/}}
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{{Article summary link|lcms (v1.15)|http://www.littlecms.com/}}
{{Article summary link|Separate plugin (v0.10 and above ?)|http://www.blackfiveservices.co.uk/separate.shtml}}
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{{Article summary link|Separate plugin (v0.10 and above)|http://www.blackfiveservices.co.uk/separate.shtml}}
 +
{{Article summary link|Separate+ plugin (v0.5.5)|http://cue.yellowmagic.info/softwares/separate-plus/}}
 
{{Article summary heading|Related articles}}
 
{{Article summary heading|Related articles}}
 
{{Article summary wiki|Using lprof to profile monitors}}
 
{{Article summary wiki|Using lprof to profile monitors}}
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== Before you read ==
 
== Before you read ==
  
Before you install the Separate plugin for The GIMP, you need to know if you really need it.
+
Before you install the Separate or Separate+ plug-in for Gimp, you need to know if you really need it.
  
There has been much debate about the merits of using The GIMP. Most of the heated discussions revolve around the fact that The GIMP does not support CMYK mode. However, you have to understand that the topic is more important to DTP professionals than other users (photographers, web artists, home users). CMYK color model (or CMYK mode) is used mostly by DTP professionals that need to output images intended for printing on a commercial press. For an average home user or even professional photographers, support for separating images using CMYK color is not necessary. Most ink-jet and color laser printers print color images using sRGB color, so you do not need CMYK support.
+
There has been much debate about the merits of using Gimp. Most of the heated discussions revolve around the fact that Gimp does not support CMYK mode. However, you have to understand that the topic is more important to DTP professionals than other users (photographers, web artists, home users).  
  
=== Root access ===
+
CMYK color model (or CMYK mode) is used mostly by DTP professionals that need to output images intended for commercial printing. For an average home user or even professional photographers, support for separating images using CMYK color is not necessary.
  
You will need root access in order to install the plugin.
+
Even when you see Cyan, Magenta, Yellow, and Black cartridges in your ink-jet or color laser printer, it doesn't mean that you need to feed it a CMYK file. In fact, most of them actually accept only RGB images.
  
=== Note on Adobe ICC profiles ===
+
=== What you will need ===
  
[http://www.adobe.com/ Adobe Systems] offers a nice set of standard color profiles for professional use. However, before you use the products, please read the end user license agreement supplied with the .zip file. The zip file (Windows version is a zip file, and it is the preferred way to get ICC profiles) is located at Adobe's [http://www.adobe.com/support/downloads/iccprofiles/icc_eula_win_end.html support page].
+
You will need Gimp (of course), either Separate or Separate+ plugins, and ICC profiles. All of this can be installed from AUR.
 
+
'''NOTE:''' If you opt for Windows version of the package, you will need unzip to extract the files. Unzip tool can be obtained from Arch repositories.
+
 
+
=== Note on Timo Autiokari's linear gamma profiles ===
+
 
+
[http://www.aim-dtp.net/aim/download/aim_profiles.zip The profiles] found on Timo Autiokari's ''[http://www.aim-dtp.net/ Accurate Image Manipulation]'' website are not typical RGB color-space profiles. These profiles are meant to be used in a very high-end ''linear workflow''. The linear workflow is a powerful concept that yields superior results in some cases, but it is out of scope of this article. Plenty of tutorials and examples are available on his site, so go there if you are looking for information on linear workflow and linear editing techniques. The original author of this article has no plans of writing an article about the linear workflow, but some Photoshop-related articles may be found in the [http://www.aim-dtp.net/aim/photoshop/index.htm Photoshop section] of Timo Autiokari's web site.
+
 
+
=== Note on Scribus 1.3.3.5 ===
+
 
+
Images separated using Separate plugin are not handled correctly by [http://www.scribus.net/ Scribus]. This issue is confirmed in a [http://bugs.scribus.net/view.php?id=4518 bug report] filed at Scribus' bug tracker. This is not a Separate bug. The image created using Separate is, indeed, a valid CMYK image.
+
 
+
Although Scribus does not handle separated images well, it does separation on its own, so it is not an unsurmountable problem. It is still advisable to downgrade to earlier versions for a more complete workflow.
+
  
 
== About CMYK color model ==
 
== About CMYK color model ==
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When printing an image on a commercial press, it needs to be printed one primary (or Black) at a time. Therefore the original (usually a digital RGB image, or a printed photograph) needs to be separated into Cyan, Magenta, Yellow, and Black components.
 
When printing an image on a commercial press, it needs to be printed one primary (or Black) at a time. Therefore the original (usually a digital RGB image, or a printed photograph) needs to be separated into Cyan, Magenta, Yellow, and Black components.
  
The lack of support for this kind of separation made The GIMP unattractive to DTP professionals.
+
The lack of support for this kind of separation made Gimp unattractive to DTP professionals.
  
== ICC color profiles ==
+
== About ICC color profiles ==
  
 
Since reproduction of both RGB and CMYK colors are specific to the device (or inks) used to produce images, a concept of color-spaces was invented. Color-spaces formulate the relationship of physical color and the color model that we use to describe them. Those relationships (functions) can be packaged as a file in the form of ICC profiles.
 
Since reproduction of both RGB and CMYK colors are specific to the device (or inks) used to produce images, a concept of color-spaces was invented. Color-spaces formulate the relationship of physical color and the color model that we use to describe them. Those relationships (functions) can be packaged as a file in the form of ICC profiles.
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The ICC profiles are used to describe the way colors are reproduced in a system, be it a monitor, a scanner, or a printing press. When separating images for press, we use the source profile (the color-space of the image to be separated) and the target profile (the color-space of the printing press the image is intended for).
 
The ICC profiles are used to describe the way colors are reproduced in a system, be it a monitor, a scanner, or a printing press. When separating images for press, we use the source profile (the color-space of the image to be separated) and the target profile (the color-space of the printing press the image is intended for).
  
== CMYK color and The GIMP ==
+
== About CMYK color and Gimp ==
  
The GIMP still lacks full CMYK color model support. The ability to separate and then ''edit'' an image in CMYK mode is still a long way down the list of features to be added (if on the list at all). However, there is a plugin called ''Separate'' that offers a partial solution to the problem.
+
Gimp still lacks full CMYK color model support. The ability to separate and then ''edit'' an image in CMYK mode is still a long way down the list of features to be added (if on the list at all). However, there is a plug-in called ''Separate'' that offers a partial solution to the problem.
  
 
Separate plugin has following abilities:
 
Separate plugin has following abilities:
Line 73: Line 62:
 
* attach ICC profiles to separated image files
 
* attach ICC profiles to separated image files
  
The GIMP itself offers a smaller set of CMYK-related functions:
+
Separate+ plug-in has the same features as Separate, but it also has:
 +
 
 +
* ability to convert from one RGB profile to another
 +
* duotone support
 +
 
 +
Gimp itself offers a smaller set of CMYK-related functions:
  
 
* display of CMYK values when using color picker
 
* display of CMYK values when using color picker
* soft-proofing colors (via Display Filters)
+
* soft-proofing colors via Display Filters (not recommended)
 +
* soft-proofing colors via color management settings
  
== Separate plugin for The GIMP ==
+
== Getting the software ==
  
=== Installing using AUR ===
+
=== Separate plug-in for Gimp ===
  
Get the [http://aur.archlinux.org/packages.php?do_Details=1&ID=11438 gimp-plugin-separate] package from AUR and install it using [http://wiki.archlinux.org/index.php/Makepkg makepkg].
+
==== Installing using AUR ====
  
=== Installing Separate manually ===
+
Get the [http://aur.archlinux.org/packages.php?do_Details=1&ID=11438 gimp-plugin-separate] package from AUR and install it using [[makepkg]].
 +
 
 +
==== Installing Separate manually ====
  
 
Once you have obtained the [http://www.blackfiveservices.co.uk/linux_resources/separate-gimp2-0.3_linux.tar.gz source tarball], you can unpack it using the usual tar command:
 
Once you have obtained the [http://www.blackfiveservices.co.uk/linux_resources/separate-gimp2-0.3_linux.tar.gz source tarball], you can unpack it using the usual tar command:
Line 90: Line 87:
 
  tar xvf separate-VERSION.tar.gz
 
  tar xvf separate-VERSION.tar.gz
  
where VERSION would be the version of Separate plugin (0.1 at the time of this writing).
+
where VERSION would be the version of Separate plug-in (0.1 at the time of this writing).
  
Copy a file called ''separate'' (located inside the extracted ''separate'' directory) into The GIMP's plugin directory:
+
Copy a file called ''separate'' (located inside the extracted ''separate'' directory) into Gimp's plug-in directory:
  
 
  cp separate/separate /usr/lib/gimp/GIMPVERSION/plug-ins/
 
  cp separate/separate /usr/lib/gimp/GIMPVERSION/plug-ins/
  
where GIMPVERSION would be the major version number of The GIMP (2.0 at the time of this writing).
+
where GIMPVERSION would be the major version number of Gimp (2.0 at the time of this writing).
  
When you start The GIMP the Separate will be recognized and reachable through ''Image > Separate'' menu.
+
When you start Gimp the Separate will be recognized and reachable through ''Image > Separate'' menu.
  
=== Install Adobe ICC profiles ===
+
=== Separate+ plug-in ===
  
Download the ICC profiles from Adobe's [http://www.adobe.com/support/downloads/iccprofiles/icc_eula_win_end.html support page] (read the agreement and click ''Accept'' at the bottom of the page).
+
==== Installing using AUR ====
  
Create a directory for the profiles:
+
Grab the [http://aur.archlinux.org/packages.php?ID=32995 gimp-plugin-separate+] package and install it using [[makepkg]].
  
mkdir -p /usr/share/color/icc
+
==== Installing manually ====
  
extract the downloaded zip file and copy the contents of CMYK and RGB directories into the created folder.
+
To install manually, get the zip file from [http://sourceforge.jp/projects/separate-plus/downloads/42977/separate+-0.5.5.zip/ Sourceforge.jp download page], unpack it and issue the following commands:
  
  unzip AdobeICCProfiles_end-user.zip
+
  make
  cd Adobe\ ICC\ Profiles\ \(end-user\)/
+
  sudo make install
cp CMYK\ Profiles/* /RGB\ Profiles/* /usr/share/color/icc
+
  
=== Separating a RGB image ===
+
If you don't have [[sudo]] on your system, you can build like this:
  
Open an image in The GIMP. From the ''Image'' menu, open the ''Separate'' sub-menu and pick ''Separate (to Colour)''.
+
make
 +
su
 +
# Enter root password
 +
make install
 +
 
 +
When you start Gimp the Separate+ will be reachable through ''Image > Separate'' menu.
 +
 
 +
=== Install ICC profiles ===
 +
 
 +
If you are using the Separate plug-in package from AUR, you already have the profiles installed. However, if you built Separate yourself, or you are using Separate+, you will need to install ICC profiles.
 +
 
 +
==== Installing from AUR ====
 +
 
 +
To install ICC profiles from AUR, you need to get [http://aur.archlinux.org/packages.php?ID=32997 eci-icc] and/or [http://aur.archlinux.org/packages.php?ID=32998 adobe-icc] packages (and optionally [http://aur.archlinux.org/packages.php?ID=32999 srgb-icc] package) and install them with [[makepkg]].
 +
 
 +
==== Install manually ====
 +
 
 +
Before you download and install profiles manually, you need to know that the standard location for ICC profiles is ''/usr/share/color/icc''. You have to create this directory and copy any profiles there. Another standard location is ''~/.color/icc''.
 +
 
 +
You can obtain ICC profiles from [http://www.adobe.com/support/downloads/product.jsp?product=62&platform=windows Adobe] and [http://www.eci.org/doku.php?id=en:downloads ECI].
 +
 
 +
Extract the downloaded zip file(s) and copy the contents of CMYK and RGB directories into one of the directories we have mentioned above.
 +
 
 +
== Separating a RGB image ==
 +
 
 +
Open an image in Gimp. From the ''Image'' menu, open the ''Separate'' sub-menu and pick ''Separate (to Colour)''.
  
 
Choose a source (RGB) and destination (target, CMYK) profile and click ''OK''.
 
Choose a source (RGB) and destination (target, CMYK) profile and click ''OK''.
Line 122: Line 143:
 
This will open another window with the CMYK color version. You can see that there are 5 layers total.
 
This will open another window with the CMYK color version. You can see that there are 5 layers total.
  
Pick ''Save...'' from the ''Separate'' sub-menu and save the file in TIFF format with an attached (embedded) ICC profile.
+
Pick ''Save...'' (or ''Export...'' in Separate+) from the ''Separate'' sub-menu and save the file in TIFF format with an attached (embedded) ICC profile.
  
=== Working on a separated image ===
+
You can only separate flattened images, so it is recommended that you save a new copy of the image before you create the CMYK TIFF.
  
If you want to work on a separated image you need to be intimately familiar with the way CMYK images work. If you look at The GIMP's Layers window after separating an image, you will witness the ingenious way in which the separation is done. However, editing the image is not as simple as with commercial software like Adobe's Photoshop.
+
== Working on a separated image ==
 +
 
 +
If you want to work on a separated image you need to be intimately familiar with the way CMYK images work. If you look at Gimp's Layers window after separating an image, you will witness the ingenious way in which the separation is done. However, editing the image is not as simple as with commercial software like Adobe's Photoshop.
  
 
Basically, you need to work with grayscale values of each primary color (plus Black). All the tools are available, but you only get apply them layer by layer and in grayscale.
 
Basically, you need to work with grayscale values of each primary color (plus Black). All the tools are available, but you only get apply them layer by layer and in grayscale.
Line 135: Line 158:
  
 
Go to the ''View'' menu and pick ''Display Filters...'' option. From the list of available filters, pick ''Color Proof'' (at the bottom in The GIMP version 2.2.13). Click on the right arrow button between the two lists and the ''Color Proof'' filter will be placed into the list of active filters. Click on it (the one in the active filters list) and you will get a few options below.
 
Go to the ''View'' menu and pick ''Display Filters...'' option. From the list of available filters, pick ''Color Proof'' (at the bottom in The GIMP version 2.2.13). Click on the right arrow button between the two lists and the ''Color Proof'' filter will be placed into the list of active filters. Click on it (the one in the active filters list) and you will get a few options below.
 +
 +
Although this seems very convenient, experience has proven that this is '''not''' a reliable method of soft-proofing. Instead of soft-proofing using the display filter, you are advised to properly configure Gimp's color management system and enable the ''Print simulation'' mode.
  
 
=== Intent ===
 
=== Intent ===
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== Soft-proofing with Separate's proof function ==
 
== Soft-proofing with Separate's proof function ==
  
'''NOTE:''' The original author was unsure if the source profile should be a monitor profile or the image's RGB profile. The method below may not work. You have been warned!
+
Separate itself offers a way of soft-proofing color. This method of soft-proofing is not dynamic: it does not update as you edit the image, but acts more like a one-time preview. However, it is far more accurate than The GIMP's soft-proofing using ''Color Proof'' display filter. Basically, the proof function converts the image to RGB space using ''absolute colorimetric'' intent. It is supposed to offer a side-by-side match to the printed copy.
  
Separate itself offers a way of soft-proofing color. This method of soft-proofing is not dynamic: it does not update as you edit the image, but acts more like a one-time preview. However, it is supposed to be far more accurate than The GIMP's soft-proofing using ''Color Proof'' display filter. Basically, the proof function converts the image to RGB space (probably the monitor space) using ''absolute colorimetric'' intent. It is supposed to offer a side-by-side match to the printed copy.
+
To soft-proof with Separate's proof function, you first [[#Separating a RGB image|separate an image]] and then pick ''Proof'' from ''Separate'' sub-menu. Source profile is your minitor's RGB profile (you can use [[Using lprof to profile monitors|lprof to profile your monitor]] and create an ICC profile). The destination profile is the ICC profile of a your image will be output to.
 
+
To soft-proof with Separate's proof function, you first [[#Separating a RGB image|separate an image]] and then pick ''Proof'' from ''Separate'' sub-menu. Source profile is your monitor's profile (you can use [[Using lprof to profile monitors|lprof to profile your monitor]] and create an ICC profile). The destination profile is the ICC profile of a your image will be output to.
+
  
 
Click ''OK'' and you will be presented with an RGB image of how the printed image would look like.
 
Click ''OK'' and you will be presented with an RGB image of how the printed image would look like.
 +
 +
== Soft-proofing with Separate+'s proof function ==
 +
 +
Separate+ acts the same way as Separate.
 +
 +
== What RGB profile to use for images? ==
 +
 +
Although Adobe RGB is a common profile, sRGB profiles (especially the new v4 version also [http://aur.archlinux.org/packages.php?ID=32999 available in the AUR]) is also used often.
  
 
== Resources ==
 
== Resources ==

Revision as of 02:51, 20 December 2009

Template:Article summary start Template:Article summary text Template:Article summary heading Template:I18n entry Template:Article summary heading Template:Article summary link Template:Article summary link Template:Article summary link Template:Article summary link Template:Article summary heading Template:Article summary wiki Template:Article summary end

Before you read

Before you install the Separate or Separate+ plug-in for Gimp, you need to know if you really need it.

There has been much debate about the merits of using Gimp. Most of the heated discussions revolve around the fact that Gimp does not support CMYK mode. However, you have to understand that the topic is more important to DTP professionals than other users (photographers, web artists, home users).

CMYK color model (or CMYK mode) is used mostly by DTP professionals that need to output images intended for commercial printing. For an average home user or even professional photographers, support for separating images using CMYK color is not necessary.

Even when you see Cyan, Magenta, Yellow, and Black cartridges in your ink-jet or color laser printer, it doesn't mean that you need to feed it a CMYK file. In fact, most of them actually accept only RGB images.

What you will need

You will need Gimp (of course), either Separate or Separate+ plugins, and ICC profiles. All of this can be installed from AUR.

About CMYK color model

If you are not interested in the theory, you may skip straight to the heading on CMYK color support in The GIMP.

First off, the proper name for CMYK mode, as it is commonly known, is CMYK color model. It is called a color model, because it represents a standard way of describing colors.

The color model is also called a subtractive color model, as opposed to additive (that is RGB) color model. Words additive and subtractive suggest that light, which is essential for perception of color, is either added or subtracted before it reaches the eye. The choice of primary colors is based on belief that the combination of Red, Green, and Blue (for RGB) or Cyan, Magenta, Yellow (for CMYK) produce the greatest range visible colors.

Subtraction of light occurs when an ink absorbs part of the light that falls on it. The rest is reflected and reaches our eyes. Different inks absorb different parts of the light's spectrum, and the combination of C-M-Y inks yields the greatest range of different colors.

Ideally, subtraction of all light, that is when Cyan, Magenta, and Yellow are mixed together at their full density, we should get black (i.e., no light reflected, fully absorbed by ink). However, this is usually not true in the real world because the inks are semi-transparent and the white paper below reflects some of the light. The use of additional Black ink in printing (K in CMYK stands for Key, or blacK) is due to this fact. It adds the necessary density to the image and makes black a black.

When printing an image on a commercial press, it needs to be printed one primary (or Black) at a time. Therefore the original (usually a digital RGB image, or a printed photograph) needs to be separated into Cyan, Magenta, Yellow, and Black components.

The lack of support for this kind of separation made Gimp unattractive to DTP professionals.

About ICC color profiles

Since reproduction of both RGB and CMYK colors are specific to the device (or inks) used to produce images, a concept of color-spaces was invented. Color-spaces formulate the relationship of physical color and the color model that we use to describe them. Those relationships (functions) can be packaged as a file in the form of ICC profiles.

The ICC profiles are used to describe the way colors are reproduced in a system, be it a monitor, a scanner, or a printing press. When separating images for press, we use the source profile (the color-space of the image to be separated) and the target profile (the color-space of the printing press the image is intended for).

About CMYK color and Gimp

Gimp still lacks full CMYK color model support. The ability to separate and then edit an image in CMYK mode is still a long way down the list of features to be added (if on the list at all). However, there is a plug-in called Separate that offers a partial solution to the problem.

Separate plugin has following abilities:

  • separate a RGB image
  • color management (using ICC profiles and lcms)
  • soft-proofing colors
  • attach ICC profiles to separated image files

Separate+ plug-in has the same features as Separate, but it also has:

  • ability to convert from one RGB profile to another
  • duotone support

Gimp itself offers a smaller set of CMYK-related functions:

  • display of CMYK values when using color picker
  • soft-proofing colors via Display Filters (not recommended)
  • soft-proofing colors via color management settings

Getting the software

Separate plug-in for Gimp

Installing using AUR

Get the gimp-plugin-separate package from AUR and install it using makepkg.

Installing Separate manually

Once you have obtained the source tarball, you can unpack it using the usual tar command:

tar xvf separate-VERSION.tar.gz

where VERSION would be the version of Separate plug-in (0.1 at the time of this writing).

Copy a file called separate (located inside the extracted separate directory) into Gimp's plug-in directory:

cp separate/separate /usr/lib/gimp/GIMPVERSION/plug-ins/

where GIMPVERSION would be the major version number of Gimp (2.0 at the time of this writing).

When you start Gimp the Separate will be recognized and reachable through Image > Separate menu.

Separate+ plug-in

Installing using AUR

Grab the gimp-plugin-separate+ package and install it using makepkg.

Installing manually

To install manually, get the zip file from Sourceforge.jp download page, unpack it and issue the following commands:

make
sudo make install

If you don't have sudo on your system, you can build like this:

make
su
# Enter root password
make install

When you start Gimp the Separate+ will be reachable through Image > Separate menu.

Install ICC profiles

If you are using the Separate plug-in package from AUR, you already have the profiles installed. However, if you built Separate yourself, or you are using Separate+, you will need to install ICC profiles.

Installing from AUR

To install ICC profiles from AUR, you need to get eci-icc and/or adobe-icc packages (and optionally srgb-icc package) and install them with makepkg.

Install manually

Before you download and install profiles manually, you need to know that the standard location for ICC profiles is /usr/share/color/icc. You have to create this directory and copy any profiles there. Another standard location is ~/.color/icc.

You can obtain ICC profiles from Adobe and ECI.

Extract the downloaded zip file(s) and copy the contents of CMYK and RGB directories into one of the directories we have mentioned above.

Separating a RGB image

Open an image in Gimp. From the Image menu, open the Separate sub-menu and pick Separate (to Colour).

Choose a source (RGB) and destination (target, CMYK) profile and click OK.

This will open another window with the CMYK color version. You can see that there are 5 layers total.

Pick Save... (or Export... in Separate+) from the Separate sub-menu and save the file in TIFF format with an attached (embedded) ICC profile.

You can only separate flattened images, so it is recommended that you save a new copy of the image before you create the CMYK TIFF.

Working on a separated image

If you want to work on a separated image you need to be intimately familiar with the way CMYK images work. If you look at Gimp's Layers window after separating an image, you will witness the ingenious way in which the separation is done. However, editing the image is not as simple as with commercial software like Adobe's Photoshop.

Basically, you need to work with grayscale values of each primary color (plus Black). All the tools are available, but you only get apply them layer by layer and in grayscale.

Soft-proofing with Display Filters

Given the circumstances, the best way to create a solid CMYK image would be to work in RGB mode, but enable soft-proofing. Soft-proofing is the method of adjusting the on-screen display of colors to match the final print. In the newer versions of The GIMP, soft-proofing is made possible via Display Filters.

Go to the View menu and pick Display Filters... option. From the list of available filters, pick Color Proof (at the bottom in The GIMP version 2.2.13). Click on the right arrow button between the two lists and the Color Proof filter will be placed into the list of active filters. Click on it (the one in the active filters list) and you will get a few options below.

Although this seems very convenient, experience has proven that this is not a reliable method of soft-proofing. Instead of soft-proofing using the display filter, you are advised to properly configure Gimp's color management system and enable the Print simulation mode.

Intent

The color proof (rendering) intent can be one of the following:

  • perceptual
  • relative colorimetric
  • saturation
  • absolute colorimetric

Perceptual and relative colorimetric are most common.

Perceptual compresses or expands the full color range of source color-space into the full color range of target color-space.

Relative colorimetric intent adjusts the white (white point) of source space and then adjusts the rest of the source colors accordingly. Source colors outside the target space are mapped to closest reproducible colors. In some software, this is also called proof intent.

Saturation intent keeps the saturation of the source colors even if the colors get distorted in the target space. This intent is still considered experimental and you may get unexpected (if not undesirable) results.

Absolute colorimetric leaves overlap of source and target space intact and maps source colors outside the target space are mapped to closest reproducible colors.

Profile

For color proofing, we usually use the profile of the device that image is to be printed on. For testing purposes, you may use any of the Adobe profiles mentioned aobve.

Soft-proofing with Separate's proof function

Separate itself offers a way of soft-proofing color. This method of soft-proofing is not dynamic: it does not update as you edit the image, but acts more like a one-time preview. However, it is far more accurate than The GIMP's soft-proofing using Color Proof display filter. Basically, the proof function converts the image to RGB space using absolute colorimetric intent. It is supposed to offer a side-by-side match to the printed copy.

To soft-proof with Separate's proof function, you first separate an image and then pick Proof from Separate sub-menu. Source profile is your minitor's RGB profile (you can use lprof to profile your monitor and create an ICC profile). The destination profile is the ICC profile of a your image will be output to.

Click OK and you will be presented with an RGB image of how the printed image would look like.

Soft-proofing with Separate+'s proof function

Separate+ acts the same way as Separate.

What RGB profile to use for images?

Although Adobe RGB is a common profile, sRGB profiles (especially the new v4 version also available in the AUR) is also used often.

Resources

Here are some links that you may find interesting: