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(v13) Screens and color

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

bool setaccuratescreens -

The operator setaccuratescreens was introduced by Adobe to turn on its color and moiré-resistant screening algorithms. In principle this could have been used to control HPS in the RIP, but in fact it does nothing (except pop its bool operand), because setaccuratescreens is often used with some very specific screen angles for which Adobe Accurate Screens work, which would not be the desired angles for HPS. The operator is provided, however, because some printer description files invoke it unconditionally.

frequency angle checkscreen actualfrequency actualangle unused

The checkscreen procedure in statusdict uses the ActualFrequency and ActualAngle keys of a type 1 halftone dictionary (see [RB2], chapter 7) to determine the actual frequency and actual angle that will be used if the current spot function were to be requested at the given frequency and angle . The third value pushed on the operand stack is the number 0 (zero) (in Adobe implementations, this represents a quantitative measure of the moiré that might be produced by the screen).

        colors setprocesscolors
          processcolors colors

The statusdict procedures setprocesscolors and its query counterpart, processcolors, provide a legacy alternative to the page device key ProcessColorModel. colors is a number, 1, 3 or 4, which indicates whether a DeviceGray, DeviceRGB or DeviceCMYK printer is being used. processcolors is quite widely used, especially by some versions of QuarkXPress to determine dynamically whether it is printing to a color printer or not.

        bool setblackoverprint
          blackoverprint bool

The statusdict procedures setblackoverprint and its query counterpart, blackoverprint do not yet have equivalents in Adobe’s Level 2. In the RIP they correspond to the user parameter OverprintBlack, which determines whether or not solid black should overprint other colors even when overprinting for it is not enabled by a job. These are all discussed further in (v13) Overprinting solid black (included here only for completeness).

-  deviceinfo dict

The statusdict procedure deviceinfo provides an alternative way to using processcolors (see above) of determining the color model. It predates processcolors, it only recognizes single-color and four-color (CMYK) models, and is present only for compatibility with a recommendation made by Adobe in a developer newsletter of how to determine this information from this previously undocumented operator. It returns a dictionary containing the key /Colors whose value is 4 if the page device key /Separations is true, and 1 otherwise (even for color printers).

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