If a specified color format is one for which the number of bits per pixel used for rendering the image (*DrvBPP) is the same as the bits per pixel supported by the printer (*DevBPP multiplied by *DevNumOfPlanes), then halftoning operations are handled by GDI. An example is a *DrvBPP value of four, with *DevBPP equal to one and *DevNumOfPlanes equal to four.
For such a situation, the only halftoning methods allowed are those that GDI provides. These halftoning methods are represented in GPD files by the standard halftoning option names, which are listed under Standard Options. To specify the GDI-supported halftoning methods that you want Unidrv to allow for your printer, specify their names in *Option entries for the Halftone feature. (The Halftone feature is one of the standard printer features.)
If you specify several halftoning methods and color modes in your GPD file, and if you want to limit which halftoning methods can be selected with which color modes, use option constraints.
Unidrv uses the standard HT_PATSIZE_AUTO option if no halftoning options are specified in the GPD file. The HT_PATSIZE_AUTO option causes Unidrv to use the standard halftoning method that is optimum for the selected resolution and color mode. This enables a user to switch among various combinations of resolution and color mode without the need to know the best halftoning option for any particular combination.
When using GDI-supplied halftoning capabilities, you can provide minidriver-supplied halftone patterns.
For more information about color formats, see Handling Color Formats.