Eliminating mosaic edge transparency

I'm trying to use HitFilm Express 2017 to recreate a motion graphics effect I saw recently.  The end result looks like progressive bands of color sweeping up and across the screen in very defined columns, as though a large fan shape were being run through a mosaic filter.

My attempt was pretty simple.  Make a plane, scale it to make a wide band, and rotate it a bit.  Add a grade layer above it, and apply the Mosaic filter, with 7 horizontal blocks and 20 vertical blocks.  It gets me mostly there, but the Mosaic filter leaves semi-transparent blocks on the edges.  I want all blocks to be either 100% opaque or 100% transparent, nothing in between.  I tried adding various effects below Mosaic to tweak the levels, but couldn't find anything that fully eliminated the transparency.  The closest I got was with Posterize, but even playing with its controls I still had some slightly transparent blocks on the edges.

Any ideas on how to get this to work?


  • edited June 2017

    As you're rotating the mosaic there are 'fat' pixels that aren't full of 'normal' pixels, so they'll be semi transparent. To avoid that you can go one of two ways.

    1) Apply the Mosaic Effect to the plane - not in a Grade layer - and rotate  the plane. The 'fat' pixels will also rotate.

    2) Create the Mosaic with the Grade Layer and rotate in a separate composite. You'll get the semi-transparent 'fat' pixels, but they won't be rotated.
    Drag that comp into the main composite and apply the Levels Histogram Effect to it, select the Alpha Channel and set the Input Alpha Black and White sliders to the same value (somewhere in the middle is fine, but it's not really important) and the semi transparent 'fat' pixels will become solid, as those above the threshold you set are solid and those below disappear.

  • I would try to avoid the level histogram effect when other options are available. Levels histogram has a performance penalty compared to the curves effect or the crush blacks/white alpha effect.

  • Thanks for the tips!

    @Palacono: I definitely don't want rotated fat pixels, so this needs to be a post-Mosaic effect.  Also, because my plane is a solid color, applying Mosaic to it directly won't change its appearance.  I had tried Levels Histogram initially, but only on the default RGB setting.  Forgot that it could affect the alpha channel as well.  That was eye-opener number 1. Thanks!

    @NormanPCN: Thanks for the performance tip, and for the pointer to Crush Blacks & White Alpha.  I had tried the normal crush effect as part of my earlier testing, but somehow didn't see the alpha-specific version. That ended up being the winner.  Thank you!

  • @jsbarrett Also remember that Curves can work on individual channels just like levels. Including the Alpha channel. Adjusting the curve end points is much like, the same as, adjusting the levels end points.

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