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[Simeon Muller]

Hey Red Family,
So I wanted to try something new as I was outside a major city and they had tons of stars. I set the Epic-W up for a 1 second exposure and a 1 second FPS. When I looked at the screen and EVF it looked amazing. But now that I have the footage there are a whole bunch of, lets say, "not stars." You can notice them as the time lapse (it's sped up so you can see the dots that stay still) progresses. There are some red dots and some white.
Does anyone know what would affect this? Sensor? gain? other?
Here is the link to the youtube video for reference. Any ideas would be great. I loved the shot and the items flying though the screen, I just wish It would have been clean.
Thanks All
https://youtu.be/NxoesBf1A3Q

Simeon

[Andrew Gentle]

These hot pixels seem to be an issue for the RED sensors with long exposure times. On my Scarlet Dragon I get them at 1 s exposures and they reduce as you shorten the exposure. Black shading is helpful but doesn't seem to be able to get rid of all of them. I think all you can do is test your exposure time until they're acceptably minimal and then use a 360° shutter and Frame Processing in the RED to sum/average frames or image stacking in post (or a combination of both) to achieve the exposure time and shutter angle you desire (discarding frames to change the shutter angle).

If anyone has found a better solution then I'd love to hear about it!

[Phil Holland]

RED doesn't employ noise reduction in their cameras and the way long exposures work with digital cinema cameras in general is pretty far off from how a DSLR/Mirrorless will handle them through their image processor and likely Dark Frame Noise Reduction.

Advice from my previous experiences.

- At your location run a Sensor Calibration for your 1 second exposure, it will take a bit. The main reason is that you do this in the temperature that you'll be filming in.
- After you roll a clip/timelapse take put the Body Cap on the camera and record 30 seconds or so.

This gives you a Dark Frame image sequence that you can use to combat potential hot pixels in something like After Effects that might exist that evening.

Various other post processing techniques can help reduce noise as well. Specifically something temporally based.

[Andrew Gentle]

- After you roll a clip/timelapse take put the Body Cap on the camera and record 30 seconds or so.

This gives you a Dark Frame image sequence that you can use to combat potential hot pixels in something like After Effects that might exist that evening.

Hi Phil, the dark frame is also an excellent idea. Is the pixel information likely to be recoverable (just offset) by subtracting the dark frame or typically is this method only really good for hiding the colour peaks (the affected pixels clipping and discarding information)?


Last time I tried this I also ran the frames through Capture One, which is a photo editing program which has a 'single pixel' noise reduction mode. It didn't solve all the pixels but it helped a little. I don't think the algorithm works super well if the debayering has already been performed, it would be likely to work better with RAW photo files.

[Phil Holland]

You'll be looking to subtract the hot pixels from the motion clip, if they are static you can actually get away with using one frame as reference.

Subtraction or offset is possible, mixing some temporal calculations into the mix can help make the images cleaner as well if your beefing up the ISO. There are some interesting modes in camera to explore as well like Frame Averaging and Summing under Recording.

Timelapse is pretty much the only arena where I use still cameras for motion work these days. Having the ability to do Dark Frame NR on a per frame basis is valuable for longer 1+ second exposures for sure.

[Simeon Muller]

You'll be looking to subtract the hot pixels from the motion clip, if they are static you can actually get away with using one frame as reference.

Subtraction or offset is possible, mixing some temporal calculations into the mix can help make the images cleaner as well if your beefing up the ISO. There are some interesting modes in camera to explore as well like Frame Averaging and Summing under Recording.

Timelapse is pretty much the only arena where I use still cameras for motion work these days. Having the ability to do Dark Frame NR on a per frame basis is valuable for longer 1+ second exposures for sure.

Thanks Phil, that's a great idea. It was an experiment as I had never thought to do a time lapse with the RED but I wanted to see if it could keep up with the DSLR in that area. Not sure if I'd do it again but if I do, I'll definitely use that trick.

Simeon