N.2.2 Color Transformations

N.2.2 Color Transformations (Current)
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N.2.2.1 Profile Connection Space Transformation

The Profile Connection Space Transformation operation applies only to color images, including true color (e.g., RGB) and pseudo-color (e.g., PALETTE COLOR) images, grayscale images for which a Palette Color LUT has been specified in the Presentation State, and the RGB output values of a blending operation.

The ICC Profile is an Input Profile. That is, it describes the color characteristics of a (possibly hypothetical) device that was used to generate the input color values.

The intent is that a rendering device will use this information to achieve color consistency. Typically this will be performed by calibration of the output device to create an ICC Display or Output Profile, the conversion of pixel values using the ICC Input Profile into Profile Connection Space, followed by conversion using the ICC Display or Output Profile into values suitable for rendering on the output device. However, the exact mechanisms used are beyond the scope of the Standard to define.

Note

The means of achieving color consistency depends to a large extent on the nature of the material and the intent of the application. The process is more complicated than simply achieving colorimetric accuracy, which is trivial but does not produce satisfactory results. The transformations may take into account such matters as
- physical factors such as the ambient light of the viewing environment (viewing flare) and the nature of different illuminants
- psychovisual factors in the observer
- the preferences of the observer
- the consistency intent, whether it be to reproduce the colors perceived by an observer of
  - the original scene,
  - the media being reproduced, such as a print or transparency, as viewed under specified conditions.
Implementations of color management schemes are typically provided in operating systems, libraries and tool kits, and the exact details are usually beyond the control of the DICOM application developer. Accordingly, it is normally sufficient to define a source of pixel values, and a corresponding ICC Input Profile for the device that captured or generated them.
When a color image is rendered on grayscale display, the behavior is not defined. Since the L* value of a CIELab representation of the PCS is not dissimilar to the Barten model used in the GSDF, a reasonable approach would be to interpret it as a P-Value.

An ICC Profile is always present in a Color, Pseudo-Color or Blended Presentation State. If an ICC Profile is present in the Image then the Presentation State ICC Profile shall be used instead of the Image ICC Profile.