michaelangeletti
commented
5 years ago What a great example video! There is an entry in the AVAA for Image Lag (AKA "Comet Tails") which is also a video tube-related artifact. In this example, it looks to me like the camera is set up to record a low light scene at the start. Then when the lamp is turned on, the brightest part of the image around the lamp is completely clipped because the gain is turned way up to accommodate that low light level (or maybe the iris is way open?). I think auto-gain/auto-iris features were included on recording systems, but they weren't very sensitive. We've probably all seen recordings where the peak luminance is bouncing all over depending on where the camera is pointed, for example. I'm not sure if the bloom in this example is due to tube wear or if it is just a camera adjustment/camera setting issue. I know that bright objects will burn the targets in Vidicon tubes. There used to be a way of getting rid of the burn-in using a white card, opening up the iris on the camera, defocusing and re-burning the tube uniformly, but I think that shortened its life and reduced its sensitivity. Anyway, I don't think there is a standardized term for this with Vidicon tubes beyond what you are using now. When I know the clipping isn't resulting from something else in a given signal chain, I think I've usually called it "In-camera Clipping" around here, just to denote that the camera or a camera setting is responsible for it.
iamdamosuzuki
Hi all,
I have uploaded an example of what we typically called "Native luminance clipping" or "Luminance blooming". The error appears to be caused by old or worn-out picture tubes in tube cameras. From what I can gather, the voltage int he tube saturates in the spot where it's hit with too much light. Has anybody heard a more official term for this? In a sense it seems like "tube saturation" would work, and it's term used often by audio technicians. Thoughts?
https://archive.org/details/LuminanceBloom