What are the black marks?

[wonderboy]

http://apod.nasa.gov/apod/ap020317.html


cick into the highest resolution for this apod and let me know what the black marks are over the central two stars?

[geckzilla]

Processing artifacts. I can only speculate how exactly the black marks ended up on this one since I'm unfamiliar with the processing method used but when processing it's often extremely difficult for a computer to distinguish between a hot pixel or cosmic ray and a star. To a computer, they match the same pattern. Many times I have to go through manually and mark off all the stars in an image so I don't erase portions of them along with the hot pixels and cosmic rays.

[Chris Peterson]

http://apod.nasa.gov/apod/ap020317.html
cick into the highest resolution for this apod and let me know what the black marks are over the central two stars?

Digitally, data can be represented in different formats. It is possible to misinterpret formats such that very large numbers are taken as negative. It isn't uncommon when passing data through multiple processes, from the camera, readout, calibration, and final processing, to accidentally have this happen, with the result that some saturated pixels may be represented as black, rather than white. That's probably what is going on here.

[geckzilla]

Why do you suppose that star lacks a charge bleed while the less bright ones to the lower left of it have them?

[Chris Peterson]

Why do you suppose that star lacks a charge bleed while the less bright ones to the lower left of it have them?

There is no fully automated way to remove blooming spikes from an image (I expect you encounter this problem frequently when working with HST images). Spikes are removed by cloning, or by scaling and stacking layers made from data without blooming. I'd guess that in this case the processor manually removed the really large blooming spike(s), but didn't work on the others (or only minimally removed them).

[geckzilla]

Oh, probably so. I tend to agonize over those details so I figured none of them had been removed. Why would you leave the little ones behind? Argh! I do have a much quicker method than cloning for dealing with them though. I just use the dust and scratches filter on the layer as a smart object and paint the mask quickly with my tablet wherever I need stuff removed. I need to investigate how exactly the dust and scratches filter works but it seems fairly non-destructive compared to cloning or toying with the healing brush.