dougpeterson
Workshop Member
I think (2) is magenta in the highlights because it's blown out in some of the frames that are being averaged. It's important not to blow out pixels in a frame-averaged image. The pixels near the blow out can show purple fringing which will then average in. The same thing can happen on seculars when shooting seascapes for example.This pair of samples compares one 8-second exposure where I walked through the scene holding a flashlight (pointed at the camera) and a frame average of 8 1-second exposures with ISO adjusted to achieve the same overall exposure (ISO 50 and ISO 400).
There are two things of note:
1 - in the single frame the light streak is full exposed at 100% luminosity (RGB 255,255,255) and is completely opaque. In the stacked frame the light streak is not fully exposed (around 85% luminosity) and you can see some detail behind the light. That's due to the averaging nature of having one frame with the light and 7 frames without the light.
2 - Notice that in the averaged version the light streak is pink/magenta rather than white or gray. I've been working with my dealer to create a support case for what appears to be a problem in the calculations. Anytime a bright highlight is only present in a very small percentage of the frames it's rendered pink/magenta rather than gray. A similar stack in Photoshop would render it as gray. My guess is that it has to do with how the two green channels are handled in the calculation. It doesn't seem to matter if the highlight is from an LED, tungsten or flash source. The problem is very repeatable on my back.
I'd suggest using the Raw File Clipping Warning in live view to avoid this.