lumakey never ending fade


    Apr 13 2006 | 6:27 am
    I have problems with the lumakey. It continues to fade out and my colors get horrible. Does the lumakey gets accelerated while working with bright colors, and the erase colors does not erase them sometimes.
    Example
    jit.gl.render Stamping @erase_color 1 1 1 0.001
    (this is because my images are about blending and accumulation)
    and then
    erase_color 1 1 1 1, erase, erase_color 1 1 1 0.001
    then the
    jit.lumakey @lum 0.16 @tol 0.1 @minkey 0. @maxkey 1. @fade 0.4
    that goes to the
    jit.gl.videoplane Stamping @blend_enable 1 @blend_mode 2 9
    Maybe this question is pretty basic, but this is the question that I have.
    Any help is welcome

    • Apr 13 2006 | 9:25 pm
      Many graphics cards have an internal precision which will flatline, never reaching the target value in such an instance. This is a HW implementation issue, and it is card specific. I might suggest that you could use a solution where you toggle between a higher alpha and lower alpha every N frames to acieve the erase time you want but which will avoid the rounding issues of the HW.
      For example to achieve a fade which is close to a 0.05 alpha erase alternate between a 0.1 alpha erase and a 0 alpha erase every other frame.
      Otherwise, it sounds like you are accumulating too much color in the frame buffer of your OpenGL window with the following.
      Hope this helps.
      -Joshua
    • Apr 14 2006 | 3:18 pm
      o.kl Thanks, what is HW? and how fast do you think that the swtiching should occur? I am not able to get what is the time frame that you ar talking about to take out this error. Does that goes connected to the general gl render right? Thanks
    • Apr 15 2006 | 12:11 am
      On Apr 14, 2006, at 8:18 AM, daniela Steinsapir wrote:
      > o.kl Thanks, what is HW?
      Hardware, in this case the graphics card.
      > and how fast do you think that the swtiching should occur? I am > not able to get what is the time frame that you ar talking about to > take out this error.
      It would depend on the alpha you want to achieve and the appropriate setting necessary for your graphics card to avoid this problem. It would be a form of temporal dithering. I don't have time at the moment to draw up an example from scratch, but if you're still not able to get the results your looking for. submit an example patch with a description of what you want but are not achieving, I can modify it to try and achieve the results you are looking for.
      > Does that goes connected to the general gl render right?
      Yes.
      -Joshua