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Video issue - certain pixels and colors corrupt image

By @drkrk92021-07-21 18:34:41.996Z

So, I have been running into this issue a handful of times and I think I have isolated the cause.

For whatever reason, a certain pixel/color array will corrupt the image from that point on. Not the whole image, just from that point to the end of the screen,

I know this is hard to explain so I created a gif and test image with the behavior.
https://imgur.com/a/A4ZVq8Q

Do I have a bad raspberry pi, bad video dongle or is it something else? (I am using a hobbyist kit).

  • 5 replies
  1. Michael Lynch @michael2021-07-22 19:10:22.353Z

    This looks like an instance of this bug:

    https://github.com/tiny-pilot/tinypilot/issues/670

    It would either be a defective HDMI dongle, a bug in the capture software, or it might just be that all of this particular model HDMI dongle fail to capture that color (or that color in some particular circumstance).

    Do you have an image that consistently causes the issue? Or is it just when you use that particular program?

    Can you try reducing the frame rate to 20 (under System > Video Settings) to see if you still see this issue at other frame rates?

    1. D@drkrk92021-07-22 19:23:20.132Z

      Sure, here is the image:

      Also, the problem goes away if the FPS are <=22, if it goes to 23 and above the problem reappears.

      1. Michael Lynch @michael2021-07-23 21:13:35.392Z

        Hmm, I'm not able to reproduce this. On my hobbyist, it shows up fine.

        You said you see this issue on Linux as well?

        1. D@drkrk92021-07-23 21:20:06.205Z

          No, just in windows using chrome. TP is connected also to a windows laptop....

          I wasn't expecting this error to be reproducible; I think if it was the tinypilot itself it would be a widespread issue. I think it is very likely this is a bad dongle.... how can I exchange it for a good one (Hobbyist TP was purchased just a few days ago)?

          EDIT: Why does it look purple in your picture? The text background should be blue.

          1. Michael Lynch @michael2021-07-26 18:39:21.083Z

            I'll send you a replacement dongle, but I suspect that's not the issue. I think it's more likely that there's just something about what's on the screen that's triggering a bug in the dongle's hardware JPEG encoder, and it only appears in rare scenarios on Windows.

            But once you receive the replacement, it will be a good experiment to help us get closer to the root cause on this.

            EDIT: Why does it look purple in your picture? The text background should be blue.

            It's just color skew from the dongle's capture. The dongle's color is generally not a perfect match for the source because of compression artifacts, so it might appear differently on different systems.