Doom9's Forum - View Single Post - Layer and Overlay operation giving wrong results with RGBA image source

pancserzso · 27th June 2013, 20:03

I would like to compose two image sources on each other, using alpha blending.

My problem is that:
1. If I just simply load the image with imagesource, the result is OK (I think it just discards the alpha channel)

2. However as soon as I do an Overlay or Layer operation, Avisynth seems to handle the alpha of the image wrong.

3. I believe the problem is pre-multiplied vs. post-multiplied alpha. I found a filter especially for fixing this, avisynth-unpremultiply (https://code.google.com/p/avisynth-unpremultiply/), however it made a totally crazy buggy colors with rainbow like blends and other bugs.

Is there any way to tell AviSynth to handle the alpha in my foreground images properly?

Here is my bg image:
https://dl.dropbox.com/s/fdq7hfm679hbmh2/composebug_bg.png

My foreground image:
https://dl.dropbox.com/s/t5c8rt0psu0l56o/composebug_fg.png

How it looks in AviSynth:
https://dl.dropbox.com/s/h7412jh6e81t1pl/composebug_avisynth.png

And how it should look, as when composed in After Effect, and selecting "premultiplied" for the foreground's alpha:
https://dl.dropbox.com/s/xb9igdqd8yyby4y/ae_00000.png

This is the Avisynth script I'm trying to use (in 2.60 b4):

Code:

background = ImageSource( "e:\render_outside\draft%05d.png", 1, 5600, 24, pixel_type="RGB24" ).ConvertToRGB32()

foreground = ImageSource( "e:\render_mixer\image%05d.png", 1, 5600, 24, pixel_type="RGB32" )

Layer( background, foreground )

27th June 2013, 20:03	#1 \| Link
pancserzso Registered User Join Date: Oct 2004 Posts: 131	Layer and Overlay operation giving wrong results with RGBA image source I would like to compose two image sources on each other, using alpha blending. My problem is that: 1. If I just simply load the image with imagesource, the result is OK (I think it just discards the alpha channel) 2. However as soon as I do an Overlay or Layer operation, Avisynth seems to handle the alpha of the image wrong. 3. I believe the problem is pre-multiplied vs. post-multiplied alpha. I found a filter especially for fixing this, avisynth-unpremultiply (https://code.google.com/p/avisynth-unpremultiply/), however it made a totally crazy buggy colors with rainbow like blends and other bugs. Is there any way to tell AviSynth to handle the alpha in my foreground images properly? Here is my bg image: https://dl.dropbox.com/s/fdq7hfm679hbmh2/composebug_bg.png My foreground image: https://dl.dropbox.com/s/t5c8rt0psu0l56o/composebug_fg.png How it looks in AviSynth: https://dl.dropbox.com/s/h7412jh6e81t1pl/composebug_avisynth.png And how it should look, as when composed in After Effect, and selecting "premultiplied" for the foreground's alpha: https://dl.dropbox.com/s/xb9igdqd8yyby4y/ae_00000.png This is the Avisynth script I'm trying to use (in 2.60 b4): Code: background = ImageSource( "e:\render_outside\draft%05d.png", 1, 5600, 24, pixel_type="RGB24" ).ConvertToRGB32() foreground = ImageSource( "e:\render_mixer\image%05d.png", 1, 5600, 24, pixel_type="RGB32" ) Layer( background, foreground )