remember those old 'color tv' based on b&w screens with colored transparencies glued on top? color by picture takes a similar approach: it takes the contrast information (b&w) from the clip, but adds the color from a picture 'plastered' on top. for some uses (usually logos, watermarks, demonstrations, and very simply masking) this method is as effective as it was half a century ago. other than that it creates a nice, if sometimes disorienting effect as two sometimes radically different picture information sources are combined.
this plug-in sports our usual live preview, the ability to use any picture source (including PDF) your mac understands, arbitrarily size, scale, and position the picture, and the option to brighten the result (as this effect tends to slightly darken the overall clip)
