Why make overexposed pixels black instead of white? Just to make it extra clear that the pixel data exceeding overexposure threshold is not mistaken for valid data?
> Just to make it extra clear that the pixel data exceeding overexposure threshold is not mistaken for valid data?
Saturated pixels are not necessarily "invalid" the way cosmic ray bit flips and stuck pixels are, but setting them to zero does make the other bright but not saturated pixels much easier to identify.
Yes, because a saturated pixel might be 101% full scale, but it might also be a hundred million percent and you have no way to know. The same reason that a camera might substitute zebra stripes or a bright colour for a blown highlight in a preview as opposed to just making it white.
When using a coronagraph, it's possible that that value is all over the place (diffraction around edges, noise, etc) but you know any data "under" the coronagraph is bogus and you know which pixels are covered, because you know how the device was made, so you can mark them as bogus yourself.
The actual value in the data isn't black (0,0,0), it'll be some obviously special value that won't otherwise happen, because black is a valid value.
I suppose the idea that not-misleading data trumps aesthetically-pleasing data continues then to the press release image, even though a solid white central spot would look more familiar to people who have accidentally included the sun in a photo.
Additional bits of information? You cannot see what shape is that area if it is surrounded with a light yellow and you will miss some info if you'll do it after JPEG conversion.
Astronomy often also deals with wide ranges of pixel exposure such that it can be hard to tell the difference between overexposed and "brighter than the max on the color scale". Better to be extra clear and remove all doubt.
