Color Management


The purpose of image color management is to provide a standardized way of accurately representing image color data across a wide array of devices: digital cameras, scanners, printers, and display monitors. In the past, a limited mechanism of gamma correction was used for display devices. In ThumbsPlus, color management can be enabled separately for color, grayscale and indexed (palette-based) images.

When working with image color profiles, it is often necessary to convert an images color profile from one color space to another. Except for very dark, very light and very saturated areas of the image, or in the case of unusual color profiles, conversion of image data from one colorspace to another does not generally change the viewed appearance significantly – as long as the resultant colorspace's profile is used by the application viewing the image. However, significant changes in the underlying image data may occur. For example, consider pictures with image data in the "Wide Gamut RGB" colorspace. If these images are displayed in a typical web browser, which does not implement color profile, they appear bland and unsaturated. This is because of how the "Wide Gamut RGB" colorspace is defined. However, if these images are converted to the sRGB colorspace, they will appear normal.

The following image color profile operations are defined within ThumbsPlus:

Set: Setting an image's color profile to a given profile indicates that "the pixel data in the image *is in* the given colorspace". The given color profile will be embedded within the image file.

Convert: Converting an image to a given color profile is the process where the image's pixel values are transformed from it's current colorspace (or from sRGB if no profile is embedded within the image) to pixel values within the desired colorspace.

Remove: Removing the color profile from an image is simply the process of saving the image file without the embedded color profile. The image pixel data is unchanged, thus no implicit conversion of colorspace occurs.

Some general rules to follow when using image color management:

1.If images are being converted for public consumption (web, e-mail, etc.), the sRGB colorspace format should be used. If they are in a different colorspace, they should be converted to sRGB.
2.Once converted to sRGB, image file size can be reduced by removing the color profile before uploading. The sRGB colorspace is generally recognized as a cross-platform default.
3.If photos come from a source, generated with a known colorspace, those images should be set to use the corresponding color profile within color management aware applications. For example, some digital cameras create images in the "Adobe RGB (1998)" colorspace, so setting that profile is appropriate.
4.When editing images in Photoshop, and using "Adobe RGB (1998)" as your working profile, time can be saved by converting working images to that profile.
5.If a service bureau or print lab asks for images with a special profile, those images should be converted to that profile.
6.For screen captured images, the color profile can be set to the same profile used by the display monitor and then converted to sRGB for general use.

To configure color management options in ThumbsPlus, select Options | Viewing - Color Management from the main menu.