Pre-multiplied or not pre-multiplied, that is the question

This topic contains 4 replies, has 3 voices, and was last updated by  Dark_Photon 2 years, 3 months ago.

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  • #49134

    lefty
    Member

    Another quick question:
    Which is better to use for the pvrtc format, premultiplied alpha, or not premultiplied alpha?

    #49144

    PaulL
    Admin

    Using premultiplied alpha for textures has several advantages for any compression format, and is generally recommended.

    #49148

    lefty
    Member

    But what are the advantages exactly? Faster? or better quality?
    I experimented using the pvr texture tool on a sprite sheet. The best quality I could get was if I bleeded the orginal texture without premultiplying. If I pre multiply the alpha there are more artifacts.

    #49195

    PaulL
    Admin

    Generally, premulitpled alpha is preferred, because when interpolating values or when filtering, the calculated values will be undesired: https://developer.nvidia.com/content/alpha-blending-pre-or-not-pre

    Depending on the source image, the results of texture compression can vary, and experimenting to find the best solution for each case is sometimes necessary.

    #49210

    Here’s another excellent write-up on pre-multiplied alpha. Some of the benefits highlighted specifically relate to image compression quality:

    * http://home.comcast.net/~tom_forsyth/blog.wiki.html#%5B%5BPremultiplied%20alpha%5D%5D

    (NOTE: The forums are munging this URL, so just webseardch “premultiplied alpha tom forsyth” and the link will come right up.

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