I processed depth maps using avisynth 2.5.8 and I found out it causes color degradation

I have a depth map (from http://vision.middlebury.edu/stereo/data/scenes2001/data/imagehtml/sawtooth.html)

And two scripts
1) just_show.avs
v = ImageSource( "depth.jpg" ).Trim(0, -1) return v
2) overlay.avs
v = ImageSource( "depth.jpg" ).Trim(0, -1) return overlay( v, v, mode = "blend", opacity = 0.80) 
They have slightly different colors. ![](http://4.bp.blogspot.com/-Lj-uQIVor4c/UcP-amr12PI/AAAAAAAAAZQ/RvXjjb2Vc14/s320/just_show.png)
just show