jit.poke~ vertical bars at high scan frequencies


    Apr 09 2015 | 11:04 pm
    Hi,
    For a project that simulates slow scan TV, I'm using jit.peek~ and jit.poke~ to transfer images using horizontal and vertical sweeps. It works great at low frame rates, ie., 0.5 Hz, but as the frame rate increases, jit.poke~ seems to be 'dropping' pixels in a very regular fashion.
    Decreasing the signal vector size, running in overdrive, and increasing the audio sample rate helps. Also I have run the patch inside an up-sampling poly~ wrapper - which also helps but eventually crashes Max.
    None of these methods completely eliminate the black vertical bars.
    Here is an example patch that only uses jit.poke~. Try increasing the vertical scan rate to 1.0 Hz or greater to see the vertical bars.
    Any suggestions, workarounds, etc., would be much appreciated.
    Tom

    • Apr 10 2015 | 1:24 am
      I think I may have figured out what's causing the vertical lines.
      When phasor~ runs at higher frequencies there are fewer samples in each ramp. So in the example patch above...
      at 96 KHz SR,
      frame rate: 0.9 is 288 Hz. horizontal = 333 samples frame rate 1.0 is 320 Hz horizontal = 300 samples
      When the number of samples per horizontal sweep drops below the number of pixels (ie., 320) Then there is not enough resolution to assign a value to each pixel.The unassigned ones are blank. So, possible solutions would be:
      reducing horizontal dimension higher sample rate interpolation interlacing
      Here is a link to video and revised patch: http://youtu.be/MfZOK6qNBiA
      Tom