4 Replies Latest reply on Sep 21, 2008 12:10 AM by Dan Isaacs

    Flicker removal on horizontal lines and screen capture text

      Hi All,

      I often have to include a PC screen capture (such as an Excel screen) in a video. How do I minimise the amount of flicker when playing back on a CRT.

      I understand the problem is in the interlacing. I have tried the anti-flicker filter and this just seems to make things softer without much improvement in the flicker.

      I have seen a post which recommends using progressive frames for still images but does not explain how to do this.

      Any assistance gratefully received!

      Regards,
      Duncan Rosie.
        • 1. Re: Flicker removal on horizontal lines and screen capture text
          akribie Level 2
          Here's a few thoughts to get the ball rolling...

          The closer the size of the source is to the video frame size, the less problems you are likely to see when converting to video. If you can see it clearly in an 800x600 (for example) window on the computer screen, you'll be well on the way to seeing it OK on video.

          Avoid small and serif fonts and white horizontals.

          If you are making NTSC projects, keep within the color gamut (15-235).
          • 2. Re: Flicker removal on horizontal lines and screen capture text
            Dan Isaacs Level 2
            > If you are making NTSC projects, keep within the color gamut (15-235).

            That should be 16-235. And, assuming you are working with RGB files, Premiere and/or Encore will automatically scale the RGB to fit within the 16-235 luminance range. PAL also uses the same legal luminance range. It is not exclusive to NTSC.

            Here is decent trick -- it may not eliminate your flicker, but it will greatly help offset the severe blurring that occurs when applying Anti-flicker or variants of this technique (such as a vertical gaussian blur) to screen captures of GUIs, spreadsheets, etc.

            1.) Open the screen capture bitmap file in Photoshop and scale it to exactly 200% using "Nearest Neighbor" resizing
            2.) Bring that file into Premiere and use Motion to scale it to fit (scale with be 50% of what it was before you resized it)
            3.) Apply Anti-flicker filter as neeeded

            The nearest neightbor resizing method makes for "blocky" resizing that is horrendous with photos, but it ideal for screen captures -- so long as you only scale by 200%, %300, %400, etc.

            This generates "extra pixels" by replicating exisitng ones that will help:

            a.) The appearance of the image when scaled to compensate for aspect ratio
            b.) Maintain better legibility even when strong softening filters (such as Anti-flicker @ 1.0) are applied
            c.) Allow for tighter zoom-ins of your screen shots while maintaining relatively sharp edges
            • 3. Re: Flicker removal on horizontal lines and screen capture text
              Level 1
              OK, I'll try the up/down rezzing trick and see if it works.

              With screen captures I always make them the same size as the video frame - 1024 x 576 for current work.

              With still photos I generally use the full res jpg and scale down in CS3 from there, photos are not a problem.

              Regards,
              Duncan Rosie
              • 4. Re: Flicker removal on horizontal lines and screen capture text
                Dan Isaacs Level 2
                Hi Duncan -- try it out. Results will be less dramatic for widescreen stuff than 4x3 (and NTSC 4x3 even more so, as the square pixel image needs to be stretched horizontally to fill the frame).

                But this method should get you an image that is horizontally sharper and vertically softer, which may translate better to interlaced screens.