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AR# 57278

LogiCORE IP Video On Screen Display (OSD) v5.01.a, v6.0, v6.0 (Rev. 1) and v6.0 (Rev. 2) - What is the valid range for the Global Alpha Value for each layer?

Description

What is the valid range for the Global Alpha Value for each layer?

Solution

For all versions of the Video On Screen Display (OSD), the full range of the Global Alpha Value is:
  • 0- 256 (0x100) - 8-bit - a maximum value of 256 is 0% transparent (100% opaque)
  • 1-1024 (0x400) - 10-bit - a maximum value of 1024 is 0% transparent (100% opaque)
  • 1-4096 (0x1000) - 12-bit - a maximum value of 4096 is 0% transparent (100% opaque)

Video On Screen Display (OSD) v5.01.a:
Due to the size of the registers, the working range is limited to (2^(DATA_WIDTH) - 1) in both the GUI and via the AXI-4 Lite interface.
Because the full global alpha range is (2^DATA_WIDTH) the core layers cannot be full opacity. The maximum they can be set to is (2^DATA_WIDTH)/(2^(DATA_WIDTH-1)), which though it is not completely opaque it as close to 0% transparent (100% opaque) as is possible in the OSD v5.01.a.

For example, if the input bit width is 8, then the maximum internal global alpha value will actually be 256 (2^DATA_WIDTH)), but the maximum value that could be set is 255 (2^(DATA_WIDTH) - 1).
The maximum global alpha value for each data width is:
  • 8-bit - (2^(DATA_WIDTH) - 1) = 256 for a maximum opacity of 255/256
  • 10-bit - (2^(DATA_WIDTH) - 1) = 4095 for a maximum opacity of 1023/1024
  • 12-bit - (2^(DATA_WIDTH) - 1) = 4095 for a maximum opacity of 4095/4096

Video On Screen Display (OSD) v6.0 and v6.0 (Rev. 1):
In the Video On Screen Display (OSD) v6.0 and v6.0 (Rev. 1), the Global Alpha Value core registers were updated to support the full range of (2^DATA_WIDTH), but the GUI still limits this setting to (2^(DATA_WIDTH) - 1).

A user can work around the GUI limitation by updating the registers via the AXI4-Lite interface, using the MAX values listed at the beginning of the solution (2^DATA_WIDTH). The range for the Global Alpha Value, can be found in the Video On-Screen Display v6.0 Product Guide (PG010).

Video On Screen Display (ODS) v6.0 (Rev. 2) and later:
The Video On-Screen Display (OSD) v6.0 (Rev. 2) and later GUI has been updated to support the full available range for the Global Alpha Value.

For a detailed list of LogiCORE IP Video On Screen Display Release Notes and Known Issues, see (Xilinx Answer 33257).
For a detailed list of LogiCORE IP Video On Screen Display Release Notes and Known Issues for Vivado 2013.1 and newer tool versions, see (Xilinx Answer 54539).

Linked Answer Records

Master Answer Records

AR# 57278
Date Created 08/28/2013
Last Updated 09/17/2013
Status Active
Type General Article
IP
  • On-Screen Display