Grab quality jit.qt.grab


    Dec 02 2008 | 10:28 pm
    Just comparing the quality of my 640 x 480 web cam in both Max/Jitter and Quartz composer. Even with the quality set to max and trying the video modes the image in Jitter is pixelated a bit compared to QC. Is this expected, or am I missing something? For my comparison I adapted the jit.qt.grab help file to be 640 x 480.
    Carl

    • Dec 03 2008 | 11:33 am
      Are you in vmode 1 or 2? I don't believe that codec quality affects vmode 0.
      jb
    • Dec 03 2008 | 12:50 pm
      tried it in all settings including v2. Just looks a little rough (pixelated)compared to Quartz composer. I just wanted to know if this is expected. Anybody else ever do this comparison?
      This is on a MacBook pro with a ATI Radeon X1600 and a built in iSight. 640 x 480
      My problem is that the patch I have made in MAX is proving really hard (for me) to put together in Quartz Composer.
      I really like working in Jitter.
    • Dec 03 2008 | 1:20 pm
      Why don't you post your patch so I can be sure that there's nothing wrong there before looking into this.
      jb
    • Dec 03 2008 | 2:04 pm
      OK here is a basic example of the jit.qt.grab @ 640 x 480 and an example of the same thing in Quartz composer uploaded I hope. The QC patch has little pixelation compared to Max/Jitter.
    • Dec 03 2008 | 5:05 pm
      OK, I tested your patch side by side with QC using my MBP's built-in iSight. The only thing I could demonstrate is that QC neglects to close the camera driver when I quit it, and that it's hard to use (for me). I saw no difference in quality. I'm in a kind of dark room, though.
      Maybe you can post some TIFFs or something and show me what you are seeing.
      jb
    • Dec 03 2008 | 6:27 pm
      Ok this is the Quartz Composer version .png
      will post the Jitter one in the next post
    • Dec 03 2008 | 6:31 pm
      The Jitter version has significantly more pixelation. This is noticeable on the side of my face and hat.
      To some people this may seem a negligible difference but to me Quartz just looks so much better.
    • Dec 03 2008 | 6:59 pm
      OK, I think I see what's going on. It appears that you're capturing at 640x480 and then blowing up to (big)x(big) and are seeing pixels as you scale. QC almost certainly uses a GL surface for displaying images, which you could best recreate using jit.gl.videoplane and friends. Try hooking the output of jit.qt.grab to the input of the jit.gl.videoplane help file (use send or something) and see if the pixels go away.
      jb
    • Dec 03 2008 | 8:37 pm
      Well, clearly they are displaying things differently, as your aspect ratios are also different :P
    • Dec 03 2008 | 9:53 pm
      Yes. A feeble mistake but only with interpolation on can I get the same quality as I get in quartz. I have now set the rect attribute to my screen dimensions and turned on interpolation. The result is very subtly different. In fact I prefer the image in Jitter, seems to have more detail.
      I have been on Quartz for so long I am re-un-learning some stuff.
      So if my screen res is 1680 x 1050 and I send it the 640 x 480 image with interpolation on my patch is now right?
      As regards the aspect ratio is that not what is also happening with the Quartz example i.e a 640 x 480 image then displayed full screen 1680 x 1050?
      Anyway they look identical now.
    • Dec 03 2008 | 9:58 pm
      Like this?
    • Dec 04 2008 | 10:57 am
      No, like this: let your graphics card interpolate and scale for you.