10.1. About the Chroma Key IP
The IP appends either:
- A constant alpha value to each pixel.
- A conditional alpha value with conditional pixel replacement.
When you turn on Constant Alpha mode, the IP appends a single alpha value to each pixel. The constant alpha value is set at compile time using a parameter.
When you turn off Constant Alpha mode, the IP selects the alpha value to append to each pixel based on whether the pixel matches a set of conditions described in the control registers. You can also turn on pixel replacement, which allows you to set the pixel’s color plane values. These values depend on if the pixel matches the user-defined condition you define using the memory-mapped control interface.
The IP is available as full or lite variants. For more information on full and lite, refer to the Intel FPGA Streaming Video Protocol Specification. The Chroma Key IP decodes input resolutions and field type by reading image information packets for full variants or using the register interface for lite variants.