Unpremultiply

Abstract
Author	jsutinen, IanB
Version	20121231
Download	Unpremultiply.zip
Category	Masking
License	BSD 3-Clause
Discussion	Doom9 Thread

Description

AviSynth plugin to convert a premultipled RGB32 clip to straight matted alpha. AviSynth's Overlay() function requires straight matted input and will product artifacts if given a premultiplied clip. This plugin performs the appropriate conversion on the alpha channel to prevent this.

Eyeon Fusion is known to only produce premultiplied RGBA videos as well as improperly configured versions of Adobe After Effects. Other video compositing solutions may also suffer the same issue.

Requirements

• AviSynth 2.5.8 or greater
• Supported color formats: RGB32

Syntax and Parameters

Unpremultiply (clip)

clip   =

Input clip to be unpremultiplied. Input clip must be RGB32, also known as RGBA. All other input types should fail with an error message.

Examples

AviSource("RGB32OverlayClip.avi")
Unpremultiply() 

Changelog

Version       Date(D/M/Y)      Changes

20121231      31/12/2012       - The bottom row and right column of the lookup table were not being initialised.

20121227      27/12/2012       - Fix a rookie mistake in not clamping the intermediate results between 0 and 255.
                               - Also changed to uses a fast 65K lookup table instead of the slow in place idiv's.

20081229      29/12/2008       - Initial release. 

Archived Downloads

Version	Download	Mirror
20121231	Unpremultiply.zip	N/A
20081229	Unpremultiply-20081229.zip	Unpremultiply-20081229.zip

External Links

• Doom9 Forum - Layer and Overlay operation giving wrong results with RGBA image source

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