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

**URL:** <https://forums.imgtec.com/t/pre-multiplied-or-not-pre-multiplied-that-is-the-question/2310>\
**Category:** PowerVR Insider\
**Created:** [June 18, 2015, 5:34pm UTC](https://forums.imgtec.com/t/pre-multiplied-or-not-pre-multiplied-that-is-the-question/2310 "2015-06-18T17:34:18Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![lefty](https://avatars.discourse-cdn.com/v4/letter/l/85e7bf/32.png) [@lefty](https://forums.imgtec.com/u/lefty)\
**Post date:** [June 18, 2015, 5:34pm UTC](https://forums.imgtec.com/t/pre-multiplied-or-not-pre-multiplied-that-is-the-question/2310/1 "2015-06-18T17:34:18Z")

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

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**Author:** ![PaulLy](https://avatars.discourse-cdn.com/v4/letter/p/958977/32.png) [@PaulLy](https://forums.imgtec.com/u/PaulLy)\
**Post date:** [June 19, 2015, 8:30am UTC](https://forums.imgtec.com/t/pre-multiplied-or-not-pre-multiplied-that-is-the-question/2310/2 "2015-06-19T08:30:44Z")

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

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**Author:** ![lefty](https://avatars.discourse-cdn.com/v4/letter/l/85e7bf/32.png) [@lefty](https://forums.imgtec.com/u/lefty)\
**Post date:** [June 19, 2015, 9:08am UTC](https://forums.imgtec.com/t/pre-multiplied-or-not-pre-multiplied-that-is-the-question/2310/3 "2015-06-19T09:08:58Z")

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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.

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**Author:** ![PaulLy](https://avatars.discourse-cdn.com/v4/letter/p/958977/32.png) [@PaulLy](https://forums.imgtec.com/u/PaulLy)\
**Post date:** [June 23, 2015, 2:18pm UTC](https://forums.imgtec.com/t/pre-multiplied-or-not-pre-multiplied-that-is-the-question/2310/4 "2015-06-23T14:18:36Z")

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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](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.

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**Author:** ![dark\_photon](https://sea1.discourse-cdn.com/flex015/user_avatar/forums.imgtec.com/dark_photon/32/224_2.png) [@dark\_photon](https://forums.imgtec.com/u/dark_photon)\
**Post date:** [June 24, 2015, 1:23pm UTC](https://forums.imgtec.com/t/pre-multiplied-or-not-pre-multiplied-that-is-the-question/2310/5 "2015-06-24T13:23:07Z")

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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#[[Premultiplied%20alpha]](http://home.comcast.net/~tom_forsyth/blog.wiki.html#%5B%5BPremultiplied%20alpha%5D)]

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