Hi All,
I am using videomixer to compose four images.
0 -- background large, all black, alpha=0.0
1,2,3 -- foreground, small, alpha=0.5
Images 2 and three are partially overlapping.
The problem is that portions of image 2 and 3 that do not overlap are too dark.
They look faded.
Since the contribution of the background is zero, I would expect the brightness of forground images to be unchanged from original image.
I wonder if there is some problem having to do with conventions regarding pre-multiplied alpha.
Maybe I need to use special plugin to convert back to non-alpha colorspace.
My pipeline follows.
Any help greatly appreciated.
Thanks much,
Bert Douglas
videomixer name=mix
sink_0::zorder=0 sink_0::xpos=+000 sink_0::ypos=+000
sink_1::zorder=1 sink_1::xpos=+250 sink_1::ypos=-100
sink_2::zorder=2 sink_2::xpos=+100 sink_2::ypos=+200
sink_3::zorder=3 sink_3::xpos=+400 sink_3::ypos=+200
! ffmpegcolorspace
! xvimagesink name=sink force-aspect-ratio=1
videotestsrc name=src0 pattern="black"
! video/x-raw-rgb, framerate=1/10, width=1000, height=1000
! videobox name=box0 alpha=0.0
! mix.sink_0
videotestsrc name=src1 pattern="smpte"
! video/x-raw-rgb, framerate=10/1, width=400, height=300
! videobox name=box1 bottom=-200 right=-200 border-alpha=0.0 alpha=0.5
! circle name=cir1 angle=0.0 height=200
! mix.sink_1
videotestsrc name=src2 pattern="checkers-8"
! video/x-raw-rgb, framerate=10/1, width=400, height=300
! videobox name=box2 bottom=-200 right=-200 border-alpha=0.0 alpha=0.5
! circle name=cir2 angle=120.0 height=200
! mix.sink_2
videotestsrc name=src3 pattern="snow"
! video/x-raw-rgb, framerate=10/1, width=400, height=300
! videobox name=box3 bottom=-200 right=-200 border-alpha=0.0 alpha=0.5
! circle name=cir3 angle=-120.0 height=200
! mix.sink_3
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