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Thread: Non-premultiplied ARGB source with WFD_TRANSPARENCY_NONE

  1. #1
    Junior Member
    Join Date
    Mar 2011
    Posts
    5

    Non-premultiplied ARGB source with WFD_TRANSPARENCY_NONE

    According to the OpenWF spec:

    WFD_TRANSPARENCY_NONE
    cí(císrc, cídst, ?src) = císrc
    císrc and ?src represent the premultiplied source color and alpha values

    My question is on the displayed result with a non-premultiplied, ARGB (RGB with alpha) source.

    At first glance, I assumed that WFD_TRANSPARENCY_NONE would have meant that the RGB channels would go directly to the display without any change and the A channel would be ignored.

    But after rethinking this, I believe there should be an alpha effect but no transparency effect on the displayed result. Is this correct?

    This would mean that an RGB source with the same RGB content will appear differently.

  2. #2
    Junior Member
    Join Date
    Feb 2010
    Posts
    6

    Re: Non-premultiplied ARGB source with WFD_TRANSPARENCY_NONE

    Lewk,

    You have made a very good point. After a quick comparison between the OpenWFC and OpenWFD spec's, we see that the OpenWFD is missing a comment in this section. In section 7.1.7 of the OpenWFC specification, you will see the following comment:

    "If WFC_TRANSPARENCY_SOURCE is disabled, the conversion of the source to premultiplied alpha format ignores the sourceís alpha values and instead uses an alpha value of 1."

    The OpenWF working group will try to add a similar comment in the 5.8.1 section of the OpenWFD specification in the next release.

    Hopefully this answers your question. Please let us know if it does not.

    Thank you,

    Steve.

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