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by Stefan Klein 5/11/2004 this refers to patch 951941

Configuration

To use CinePaint colour management, it has to be configured for your environment. The most important step is providing the necessary ICC profiles and selecting which to use.

Profiles are selected on the colour management tab of CinePaint's preference dialog which is located in the menu File/Preferences.... First of all, however, you will have to set the path of the directory in which the profiles are stored or copy your profiles into the default directory. The directory is set in the preference dialog on the directories tab. You can enter more than one directory by separating the paths by :. All paths are absolute, but can start with ~ to denote the home directory. By default, there are two paths: "~/.color/icc" and "{prefix}/color/icc" where {prefix} is the installation prefix specified at compile time ("/usr" by default). The former is thought to hold a user's own profiles, the latter system profiles. Once you have set the paths to the profiles, you will be able to select profiles on the colour management tab of the preference dialog. Note that you need to close and reopen the preference dialog for the path changes to take effect (this is a bit unfortunate, but due to the way the preference dialog was initially written and I did not want to break with the general code structure).

There are three profile selections to be made: a default image profile, a workspace profile and a display profile. This structure has become a defacto standard or at least good practice in standard colour management workflows and related applications such as Adobe Photoshop or Apple ColorSync. The default image and workspace profile listboxes offer all profiles that were found in the profile directories, the display profile listbox only shows display profiles.

To correctly display an image, CinePaint needs to know two profiles: the profile that describes the image data and the profile that describes the display device. (The reason for there to be three profile settings instead of two is to allow you to choose your own in-house working colour space and to provided mechanisms of automated conversion into it. This will become obvious as the meaning of the three profile settings become clearer.)

The display profile is selected directly via the setting of the same name. The display profile describes the display device you are using such as your monitor and is a system-wide setting. It will be used in displaying all colour-managed images (this currently does not provide for systems using two different display devices at the same time).

The image profile is assigned to the image when it is opened. In the preference dialog you can determine how this is done. You can choose to always assign the default image profile, to never assign a profile or you can choose to be prompted for the profile to be assigned whenever you open an image. You can see which profile is currently assigned to an image from the description in the image's title bar. In principle there is another way that a profile can be assigned to an image: by embedding it in the image file itself. Several file formats such as TIFF and JPEG allow embedding profiles into the image file itself. However, detection of embedded profiles is not provided for in the current version of colour management, yet This is because its implementation is not straight-forward due to the plug-in nature of file formats in CinePaint and because it has no high priority in movie studio applications: An embedded profile easily can increase the file size by 500K. Considering that a movie consists of hundreds of thousands of individual files (one per frame of the movie) each of which naturally uses the same profile (since it was scanned using the same scanner) it would be an incredibly waste of space to embedd a profile into every single one of them. Instead you would keep one single profile in a separate file and define it as the default image profile. Embedded profiles are for example useful in pre-press applications to exchange individual images with a printer.

Having explained the display profile and the default image profile, this still leaves us with the third profile setting in the preferences. The workspace profile defines your preferred colourspace, your in-house colourspace. Most users such as newspapers, agencies or movie studios will do all their work in one fixed colourspace because standardisation greatly helps with coherent workflows and results and avoids confusion. The workspace profile is the profile that CinePaint applies to every newly created image and that it may enforce for opened image depending on user preference. As we have seen, when an image is opened, it is assigned a profile according to the rule selected in the user preferences. If this profile does not match the workspace profile, CinePaint can either ignore the mismatch and keep the image profile, automatically convert the image to the workspace or consult the user on whether to convert or not. Which action is taken depends on the preference setting "When image space doesn't match workspace". The possibilities of automatic conversion and enforcing a workspace profile will become even more appealing once CinePaint will be able to handle embedded profiles. There is one setting amongst the preferences that we have not considered yet. The default rendering intent. The images you are displaying may contain colours that cannot be reproduced on your display device. (e.g. the image could have been scanned on a scanner that can sample some colours the monitor cannot display). In these cases, CinePaint (or littlecms as the colour management module) has no choice, but to try and approximate these colours. The different approaches (with different effects) that can be taken in approximating are known as rendering intents. The four standard intents are: [explanations to follow] The default rendering intent is applied to every new display you open. You can afterwards change it for each display individually.

The number of different options and different profiles to set may seem a bit confusing, if not redundant at first. They do, however, allow the maximum flexibility. Let us consider two examples to illustrate this:

A final note: For each of the profiles settings it is possible to select no profile at all. Also, you can choose to have no profile assigned to a newly opened image. Notice, however, that CinePaint will only be able to colourmanage a given image, if you have set a display profile in the preferences and have assigned a profile to the given image. Should you forget to do so, CinePaint will remind you.

Use

Now that you are all set up, you can start to have your images colourmanaged. Most of the colourmanagement functionality unfolds in the background without the need for any direct interaction - just as it should: As the user, you can get on with your work and rely on the colours to be correct without having to think about it. Since colourmanagement causes a certain loss of performance, however, it is at your discretion whether to use it or not. Notice the entry View/Colormanage Display in each display's menu. This allows you to switch colourmanagement on or off for each display individually.

You can change the rendering intent used by CinePaint using the menu View/Rendering Intent. By default this is set to whatever you selected in the user preferences.

The title bar of each display shows you which profile is currently assigned to an image and is thus used to colourmanage it. If you want to assign a different profile you can do so by using the menu Image/Assign ICC Profile... You will be prompted for the new profile to be assigned. On offer are all profiles that were found in your profile directories. If you choose to assigne no profile, colourmanagement will be switched off for all displays of this image. (Remember that CinePaint always needs to know an image and a display profile to colourmanage)

Finally, you can convert an image's data into another profile's colourspace (as might be done automatically upon opening when the colourspaces do not match, as we have seen before). Obviously, this also requires a profile to be assigned to the image, so that CinePaint knows where to convert from. In contrast to ordinary colourmanagement which does not affect the image data, this will actually manipulate it to transfer it to the new colourspace. Again, you are prompted for a profile to convert to and in this case also for a rendering intent to use in the conversion.


comments:

house -- Fri, 04 Mar 2005 01:20:38 -0800 reply

house -- Fri, 04 Mar 2005 01:20:41 -0800 reply