Object-based color management in transparency

This page applies to Harlequin v13.1r0 and later; both Harlequin Core and Harlequin MultiRIP.

Object-based color management is described in some detail in Object-based color management, and used in many of the examples in this chapter. The principle is that each graphical object is assigned an object type and color model, with potentially different color management being applied to each of the twenty combinations of these two attributes. These may then be used to make object-based selections for rendering intents, blend space profiles, black preservation, and color management overrides.

In a transparency context, graphical objects are composited into the pixels of the backdrop raster of their transparency group. If the color requires converting, the object type and color model of the object is used in the object-based transform into the group. Each pixel of the backdrop raster touched by the object is then assigned to the object’s type and the color model of the transparency group. As new objects are composited, objects may intersect with other composited objects. As a result, the object type assigned to individual pixels may change with a top-most object wins rule.

The compositing of backdrop rasters continues down the transparency stack. Each backdrop raster is composited into its parent group. Any necessary color transforms use the object type and color model assigned to each pixel. The pixels of the parent group’s backdrop raster are assigned the object type of the last pixel to be composited into it with the same top-most object wins rule. All pixels in a backdrop raster are assigned to the color model of the group.

The object-based attributes for page groups with an ICCBased blend space follows the same rule for as for normal groups. The object type of each pixel in the backdrop raster is inherited and the color model is that of the page group. These are then used for the final transform to the output device.

Page groups with other blend spaces, for example; /DeviceCMYK, are different in that the color model of each pixel is also inherited from objects composited into it. This rule gives consistent output with object-based color management for all OverprintPreview modes, for example, if RGB images are configured to use the Perceptual intent, they appear as similar as possible with OverprintPreview active verses inactive.