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TVP5158 + TMS320DM8148 : Oscillating video-rendering in monochromatic conditions.

Philippe Pierret
Prodigy 100 points
Other Parts Discussed in Thread: TVP5158, TMS320DM8148

    Hello,

    This question deals with video systems based on TVP5158 + TMS320DM8148.

    Our system is connected to night & day cameras that switch automatically from color-mode to monochromatic-mode depending on light conditions. In low-light conditions, cameras switch to monochromatic-mode to improve visibility.

    In color-mode, everything is OK and the video is stable. In monochromatic-mode, the video oscillates vertically with a very small amplitude at a low frequency (2 upto 4 Hz).

   In monochromatic-mode, we have checked that the analog input signal has no heading color-bursts at the beginning of the lines. First, this lead us to imagine that the AGC function of the TVP5158 convertor could be the culprit, but it seems that color-burst amplitude is not taken into account by default.

   We are obliged to fix this issue for our system. Your help would be very appreciated. Best regards.

  • 0
    TI__Mastermind 43875 points
    All I can think is to experiment with the color killer threshold.

    This type of camera should not be an issue and the TVP was designed to work fine in this mode.

    BR,
    Steve
  • 0 in reply to Steve Clynes
    Prodigy 100 points

    Hello Steve,

    Thanks for your previous reply. It makes a long time, but the problem is still alive.

    The french team of TI probably did not forward the results of my last investigations to you, so you will find them hereafter.

    A first test consisted in looping back the video to the analog output as soon as possible in the µP Centaurus,

    The loopback was done by sending buffers acquired at the VIP level (Video Input Parser) back to the analog output.

    Results are the same as initial standard streaming conditions :

     - When the camera is in color mode, the video output is OK.

     - When the camera is in monochromatic mode (B&W), the video output oscillates vertically.

    A second test consisted in setting the configuration of theTVP5158 component  to « Color Killer » mode (register 16h / value 0x40). Then we can consider that in this case, the µP Centaurus always processes video data with null chroma component, whatever may be the mode of the camera (color vs. monochromatic). You will see in the attached recording that the symptoms remain the same (Please watch the attached video ...)

    These results suggest that the source of the problem doesn't lie in the nature of the video data (color Vs. B&W), but rather in the associated controls.

    At this point, a bug in the management of the analog video signal by the TVP5158 when the color-bursts are missing at the beginning of PAL lines remains the most probable reason of the malfunction in our point of view.

    Thanks a lot in advance for your technical support. Best regards.

     

            Philippe

  • 0 in reply to Philippe Pierret
    Prodigy 190 points
    Hello,
    We have a similar issue with a NTSC camera which captures images only in black and white mode.

    The video have flickering and some images missed regularly.
    TVP5158 registers status have some difficulties to identify image format : PAL or NTSC... It switches very often between these both.

    With our color cameras (PAL or NTSC): any issue.

    Do you find any solution? We are very interested by that.
    We continue to investigate this problem.
    Thank you in advance.
  • 0 in reply to user4201415
    TI__Mastermind 43875 points
    Try disabling some video formats from the auto switch registers or forcing the standard.

    See registers 0x0d and 0x0e.

    BR,
    Steve
  • 0 in reply to Steve Clynes
    Prodigy 190 points
    Yes, thank you for this suggestion.
    Force video format to NTSC improves considerably image stability.

    But it is not perfect as color image. There are some flickering on the top still persist in this mode.