(v13) Managing color in transparency

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

Different jobs will have different transparency requirements. Transparent graphical objects jobs may be painted directly onto the page. Other objects may be painted into one or more Transparency groups, in different parts of the page, as an intermediate stage prior to compositing into the final output. It is also possible to arrange transparency groups in a hierarchy with each layer composited into the next.

Transparency handling involves color conversions into the Blend space of the first transparency group, and between blend spaces of successive transparency groups, as objects are composited into successive nested groups. For this reason, there may be many color conversions between parsing a graphical object and rendering it onto the output device. Typically though, all blend spaces will be the same within any given job, which will not therefore involve color conversion. In that typical case, color management will be limited to the final conversion to the Device space, and possibly the conversion from the objects color space into the first blend space.

Color conversion into the first blend space and between blend spaces can be controlled by the setinterceptcolorspace operator, but there is a caveat that a blend space must contain both device to PCS and PCS to device conversions. This caveat excludes the possibility of using a devicelink ICC profile for color conversions between blend spaces.

The RIP maintains an artificial transparency group for the purpose of compositing into the page for those cases where a job does not explicitly set up a page group at the page level. Compositing into the Virtual device is the final stage of compositing. The virtual device will match the characteristics of the job, so it will look like an RGB device when compositing RGB colors, etc.

When a configuration requires a devicelink ICC profile for performing the conversions from the virtual device to the output device, an alternative means of providing default and override blend spaces can be supplied, again through the setinterceptcolorspace operator as explained in “setinterceptcolorspace” Chapter 17 of [HQNEXTN]. When used in this way, the RIP cannot verify that a devicelink is compatible with the last blend space, so this must be left to the expertise of personnel configuring the RIP.