Selectively Displaying Video(IM: QC)

Inside Macintosh: QuickTime Components /

Chapter 8 - Video Digitizer Components / Video Digitizer Components Reference

Selectively Displaying Video
Video digitizer components may support one of three methods of selectively
displaying video on the screen of a Macintosh computer. The three methods are key colors, alpha channels, and blend masks. For a complete description of these techniques for selectively displaying video, see "About Video Digitizer Components," which begins on page 8-3.
Your application can determine whether a video digitizer component supports selective video display by examining the component's digitizer information structure (described on page 8-20). Specifically, the vdigType field indicates the type of blending supported by the digitizer. Applications can use the VDGetDigitizerInfo function (described on page 8-24) to retrieve a component's digitizer information structure.
Some video digitizer components support the use of key colors as a mechanism for selectively displaying video on the screen of a Macintosh computer. When a key color is active, the digitizer component replaces all screen occurrences of that color with the appropriate portion of the source video. Video digitizer components that support key colors provide a number of functions to applications. Those functions are described in this section.
Your applications can use the VDSetKeyColor, VDAddKeyColor, and VDSetKeyColorRange functions to set one or more key colors for a video digitizer component. The VDGetKeyColor, VDGetNextKeyColor, and VDGetKeyColorRange functions allow your application to retrieve information about the currently
active key colors.
Alpha channels and blend masks work similarly to one another. Digitizer components that support alpha channels use a portion of each pixel value to indicate the degree of video display for that pixel. Digitizer components that support blend masks use the mask to indicate the degree of video display for corresponding pixels.
Your applications can use the VDGetMaskandValue function to determine the appropriate mask value for a desired blend level. The VDSetMasterBlendLevel function allows applications to set a blend level that applies to the entire source video image. The VDGetMaskPixMap function allows applications to retrieve the pixel map that defines the blend mask.

Subtopics

VDSetKeyColor

VDGetKeyColor

VDSetKeyColorRange

VDAddKeyColor

VDGetKeyColorRange

VDGetNextKeyColor

VDSetMasterBlendLevel

VDGetMaskandValue

VDGetMaskPixMap