# &application; Manual

## Introduction

The &app; is a framework that helps the user generate, install and manage device colors on a `GNOME desktop`. It does this to help a user match color across all devices. This gives a consistent color to an image or document, wherever it is output.

The &app; communicates the selected profiles to color-aware applications, maintaining the color across applications.

The &app; uses International Color Consortium (ICC) profiles to map device color characteristics onto a standard color space used by the `GNOME desktop`.

&app; should NOT be used to alter the appearance of your desktop. The Appearance preference tool lets you configure various aspects of how your desktop looks.

## Usage

&app; is usually started at GNOME start-up, but you can manually start &app; using:

        bash$ gcm-apply --verbose

&app; preferences dialog can be started from the GNOME Preferences Menu, but you can start this using:

        bash$ gcm-prefs --verbose

ICC profiles should be imported into the &app; by selecting a file in a nautilus window. You can also import the file using:

        bash$ gcm-import <filepath>

## Importing profiles

&application; includes a program to install profiles by simply double clicking on them.

### Import a ICC profile

#### &app; dialog after double clicking an ICC or ICM file

The install button will not show if the profile has been already installed.

## Preferences

The preferences window allows you to control:

- A device profile.

- The gamma, brightness and contrast.

### Basic Preferences

#### &app; basic tab

To alter a profile for a device.

1. Select the device.

2. Select the required profile from the list in the color profile drop down box.

If the required profile is not in the list then

1. Select "Other profile..."

2. Find the ICC profile file using the GNOME Open File dialog presented.

3. Press the Open button on the dialog.

If the profile is invalid then the profile selected for the device will not alter. Messages may be shown.

You can drag JPG and RAW files on to the main window. This will automatically create a virtual device profile that you can assign a profile to.

### Advanced Preferences

#### &app; advanced tab

This allows you to adjust a calibrated device or generated profile.

The Fine Tuning Option is only available if you configure GConf to enable it ( apps gnome-color-manager show-fine-tuning ).

CRT monitors have native gamma around 2.4 - 2.5 and LCD monitors usually emulate the same value.

Traditionally, Linux and MS Windows operating systems use image encoding of 1/2.2 and do not apply any gamma adjustment to the image or video card LUT. Therefore the overall gamma is expected to be around 1.1 (which is useful to allow for dim viewing conditions at home environment).

Apple used to use image encoding gamma close to 1/1.8 to naturally match the native gamma of printing devices (and therefore internally applied gamma adjustment of 1/1.45 before displaying images on monitor so that the images displayed correctly).

Nonetheless, since OS X (v10.6 Snow Leopard) the default image encoding gamma has also the value of 1/2.2 to meet the requirements of consumer imaging industry.

Before fine tuning the gamma in &app;, you should know what your monitor native gamma is, what display gamma you want to reach and then do the math yourself.

### Profile viewer

#### &app; profiles tab

This allows you to view details about installed profiles.

### Calibration and profiling

&application; can generate ICC profiles with supported color measuring instruments.

#### The first stage is calibration, which takes a few minutes.

#### The final stage is profiling (characterization), which can take over 15 minutes.

When calibrating and profiling a display you may have to change the color measuring instrument to operate in different modes. You may have to remove your instrument from the screen to change the modes. Ensure the instrument is put back on the screen after you have changed any settings.

#### &app; Instrument Configure Dialog

When calibrating and profiling a display connected using a VGA or DVI connection, often the type of device is not known. By answering correctly, &application; can generate better profiles for the device you are trying to calibrate and profile.

#### &app; Screen Type Dialog

When profiling a printer you can also generate images to be sent to a print shop or photograph processing agency. The profiling details will be saved, and you will need to select the correct profiling results when you receive the proofs back.

#### &app; Print Mode Dialog

## Frequently asked questions

This section list questions frequently asked about color management

### What's the difference between calibration and characterization?

Many people are initially confused about the difference between calibration and characterization. Calibration is the process of modifying the color behavior of a device. This is typically done using two mechanisms:

1. Changing controls or internal settings that it has.

2. Applying curves to its color channels.

The idea of calibration is to put a device is a defined state with regard to its color response. Often this is used as a day to day means of maintaining reproducible behavior. Typically calibration will be stored in device or systems specific file formats that record the device settings or per-channel calibration curves.

Characterization (or profiling) is recording the way a device reproduces or responds to color. Typically the result is stored in a device ICC profile. Such a profile does not in itself modify color in any way. It allows a system such as a CMM (Color Management Module) or a color aware application to modify color when combined with another device profile. Only by knowing the characteristics of two devices, can a way of transferring color from one device representation to another be achieved.

Note that a characterization (profile) will only be valid for a device if it is in the same state of calibration as it was when it was characterized.

In the case of display profiles there is some additional confusion because often the calibration information is stored in the profile for convenience. By convention it is stored in a tag called the `vcgt` tag. Although it is stored in the profile, none of the normal ICC based tools or applications are aware of it, or do anything with it. Similarly, typical display calibration tools and applications will not be aware of, or do anything with the ICC characterization (profile) information.

### Missing information for whole-screen color correction

Unfortunately, many vendor-supplied ICC profiles do not include the information required for whole-screen color correction. These profiles can still be useful for applications that can do color compensation, but you will not see all the colors of your screen change.

In order to create a display profile, which includes both calibration and characterisation data, you will need to use a special color measuring instruments callled a colorimeter or a spectrometer.

### Which color measuring instruments are supported?

GNOME Color Manager relies on ArgyllCMS to support color instruments. Thus the following display measuring instruments are supported:

- Gretag-Macbeth Eye-One Pro (spectrometer)

- Gretag-Macbeth Eye-One Monitor (spectrometer)

- Gretag-Macbeth Eye-One Display 1, 2 or LT (colorimeter)

- X-Rite ColorMunki Design or Photo (spectrometer)

- X-Rite ColorMunki Create (colorimeter)

- Pantone Huey (colorimeter)

- MonacoOPTIX (colorimeter)

- ColorVision Spyder 2 and 3 (colorimeter)

- Colorimètre HCFR (colorimeter)

### Which target types are supported?

GNOME Color Manager supports the following types of targets:

- CMP DigitalTarget

- ColorChecker 24

- ColorChecker DC

- ColorChecker SG

- i1 RGB Scan 14

- LaserSoft DC Pro

- QPcard 201

- IT8.7/2

### Where do I purchase targets from?

You can purchase targets from well-known vendors like KODAK, X-Rite and LaserSoft in various online shops. Alternatively you can buy targets from Wolf Faust at a very fair price.

## About

&app; was written by Richard Hughes richard@hughsie.com. To find more information about &app;, please visit the &application; web page.

To report a bug or make a suggestion regarding this application or this manual, follow the directions at the &application; Bug Page.

This program is distributed under the terms of the GNU General Public license as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. A copy of this license can be found at this link, or in the file COPYING included with the source code of this program.