IccColorTransformOptions Class

The compensation scales CIEXYZ toward the white point, following the algorithm published by Adobe and standardized as ISO 18619. The black point of a profile is estimated from its conversion tables or tone curves; when both are black, as between two display profiles, nothing changes. A table-based destination that cannot be converted back to the profile connection space has no measurable black point and is not compensated.

The perceptual and saturation tables of a version 4 profile give black the lightness of the perceptual reference medium (L* = 3.1373), where version 2 tables and matrix-based profiles usually give it 0. The compensation maps one to the other; without it, nothing does: converting from a version 4 table to a version 2 or matrix-based profile turns black into a dark gray, and the reverse makes the darkest grays black. Some color management systems, such as LittleCMS, compensate a version 4 destination even when asked not to.

With false, the floating-point samples keep the values outside [0, 1] that high dynamic range colors (light above the white) and wide-gamut colors (a color that the destination primaries reach with a negative component) have, at the source and at the destination. The tone curves are extended: in [0, 1] they are evaluated as usual, above 1 the function of a parametric curve continues and a sampled curve goes on with the slope of its last interval, and below 0 the curve is mirrored through its value at 0 (-f(-x) for a curve through 0, the extended transfer functions of CSS Color 4). The matrices have no range. A value that is not a number is read as 0.

Only conversions made of tone curves and matrices can do so (matrix-based profiles, the RGB and grayscale profiles of displays and color spaces): a conversion through a lookup table (an AToB or BToA table, a profile connection space in CIELAB) and a gamut mapping other than GamutMapping.Clip are refused by IccColorTransform.Create. The 8-bit and 16-bit conversions always cover the whole range of their type, which the option does not change.

The mapping happens in the profile connection space, after black point compensation and the rescaling of the ICC-absolute colorimetric intent, right before the conversion to the device values of each destination profile (each profile of a sequence that is entered from the connection space). See GamutMapping for the destinations it applies to.

The intent selects the conversion tables of table-based profiles; a profile that has no table for the intent uses its perceptual table, then its matrix and tone curves. Matrix-based profiles (most RGB and grayscale profiles) give the same result for every intent except IccRenderingIntent.AbsoluteColorimetric, which uses the colorimetric conversion and rescales the colors by the media white points of the two profiles (the illuminant of the profile connection space for a display profile and for a profile without media white point).

It applies to ImageProcessingExtensions.ConvertColorProfile on an image whose samples are PQ or HLG ones: an image without ICC profile whose CICP color description (ImageMetadata.Cicp) declares the transfer characteristics 16 or 18. Such an image is rejected when this is null: compressing the highlights changes the look of the image, which is a choice. It is ignored for every other source, and by IccColorTransform, whose sources are ICC profiles.