Minidriver-Supplied Halftoning

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Important

The modern print platform is Windows' preferred means of communicating with printers. We recommend that you use Microsoft's IPP inbox class driver, along with Print Support Apps (PSA), to customize the print experience in Windows 10 and 11 for printer device development.

For more information, see Modern print platform and the Print support app design guide.

If a specified color format is one for which the number of bits per pixel used for rendering the image (*DrvBPP) is greater than the bits per pixel supported by the printer (*DevBPP multiplied by *DevNumOfPlanes), then you must provide customized halftoning capabilities.

To provide customized halftoning capabilities, you must do the following:

  • Provide a rendering plug-in that implements the IPrintOemUni ImageProcessing method.

  • Include a Halftone*Feature entry in your GPD file and, for each customized halftoning method, include an *Option entry describing the halftoning method. (Do not use any of the option attributes for the halftone feature.)

  • Include a ColorMode *Feature entry in your GPD file. For each specified color formatting option, you must include an *IPCallbackID attribute if you want your IPrintOemUni ImageProcessing method to handle halftoning for that color format.

The following example defines two color formats and four halftoning methods. The example uses option constraints to specify which halftoning methods Unidrv should allow a user to select for each color format.

*Feature: ColorMode
{
    *Option: ColorFormat1
    {
        *Name: "Color Format 1"
        *DevBPP: 1
        *DevNumofPlanes: 4
        *ColorPlaneOrder: LIST (CYAN, MAGENTA, YELLOW, BLACK)
        *DrvBPP: 4
        *Constraints: LIST (Halftone.CustomHalftoneMethod1,
+                           Halftone.CustomHalftoneMethod2)
    }
    *Option: ColorFormat2
    {
        *Name: "Color Format 2"
        *DevBPP: 24
        *DevNumofPlanes: 1
        *DrvBPP: 8
        *IPCallbackID: 100
        *Constraints: LIST (Halftone.StandardHalftoneMethod1,
+                           Halftone.StandardHalftoneMethod2)
    }
}
*Feature: Halftone
{
    *Option: StandardHalftoneMethod1
    {
        *Name: "Standard Halftone Method 1"
    }
    *Option: StandardHalftoneMethod2
    {
        *Name: "Standard Halftone Method 2"
    }
    *Option: CustomHalftoneMethod1
    {
        *Name: "Custom Halftone Method 1"
    }
    *Option: CustomHalftoneMethod2
    {
        *Name: "Custom Halftone Method 2"
    }
}

In the example, both the ColorFormat1 and ColorFormat2 ColorMode options represent color formats that Unidrv can handle, as explained in Handling Color Formats. For ColorFormat2, an *IPCallbackID attribute is specified. If the printer user selects ColorFormat2 as the color format, Unidrv calls the printer's IPrintOemUni ImageProcessing COM method to handle halftoning. One of the method's parameters is a pointer to the string name representing the currently selected halftoning method.

For more information about halftoning, see Customized Halftoning.