4 ms·

There has been a lot of confusion about this but it is actually overexposed pixels deleted in software. From the lead author of the paper: https://twitter.com/

There has been a lot of confusion about this but it is actually overexposed pixels deleted in software. From the lead author of the paper: https://twitter.com/AndrasGaspar/status/1655680076103716878 https://twitter.com/AndrasGaspar/status/1655680076103716878

dylan604 3y ago
Black Hole Sun? There was a camera that "suffered" this problem, but can't remember the model to look it up.
- jmount 3y ago
  Film in general used to "solarize" in some situations, which would turn some over-exposed areas black.
  - dylan604 3y ago
    Maybe, but there was a specific video camera that would do this which earned the black hole sun moniker that I was thinking of. I want to say it was in the DV era, but I was never a connoisseur of that format so it was all just fuzzy memory from hearing/reading about it. I do remember looking at DV shooters with side-eye jealousy at their tiny camcorders while I was heaving full sized broadcast cameras on my shoulder.
btilly 3y ago
Thanks. Silly me for believing NASA.
kfarr 3y ago
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?
- crazygringo 3y ago
  I'm baffled as well. I think it's fairly understood that any white pixel is always understood to be probably overexposed.
  - friendlyasparag 3y ago
    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.
- eimrine 3y ago
  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.
- hn8305823 3y ago
  > 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.
  - jakear 3y ago
    Does the precise line dividing "bright but just barely not saturated" from "bright and saturated" actually matter?
    - adhesive_wombat 3y ago
      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.
asdfman123 3y ago
An mspaint.exe adjustment
jakear 3y ago
What's odd is even when downloading the full res image, the central colors are decidedly not all #000. There is a faint yet distinct radial gradient. It does not appear to be a compression artifact (format is png anyways).
- friendlyasparag 3y ago
  images released to the press sometimes get another, um, aesthetic pass. I bet if you could get ahold of the actual image file it would have the proper sentinel sentinel value (if they're still using fits files it'd be something ridiculous like -9999.)
sbierwagen 3y ago
To be clear, they were using the coronagraph: https://arxiv.org/pdf/2305.03789.pdf https://arxiv.org/pdf/2305.03789.pdf >The 23.0 µm coronagraph of MIRI uses a classic Lyot mask to achieve high contrast imaging near bright sources. The mask is rather large, providing an inner working angle (IWA) of ∼ 3.3λ/D, i.e., ∼ 2. Our data is the first complete reference PSF subtracted set of observations taken with JWST using this mode. There's some residual light and diffraction effects around the Lyot mask which they have manually deleted.
- hn8305823 3y ago
  Some images used a mask and some did not. The 25.5 micron image at the top of the article is one that did not use a mask.
geokon 3y ago
Any idea why it's not a perfect circle? Aberration in focus? And would that be pretty much equivalent to the true size of the star's corona? (seems huge..)

dylan604 3y ago

Black Hole Sun? There was a camera that "suffered" this problem, but can't remember the model to look it up.

jmount 3y ago
Film in general used to "solarize" in some situations, which would turn some over-exposed areas black.
- dylan604 3y ago
  Maybe, but there was a specific video camera that would do this which earned the black hole sun moniker that I was thinking of. I want to say it was in the DV era, but I was never a connoisseur of that format so it was all just fuzzy memory from hearing/reading about it. I do remember looking at DV shooters with side-eye jealousy at their tiny camcorders while I was heaving full sized broadcast cameras on my shoulder.

btilly 3y ago

Thanks. Silly me for believing NASA.

kfarr 3y ago

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?

crazygringo 3y ago
I'm baffled as well. I think it's fairly understood that any white pixel is always understood to be probably overexposed.
- friendlyasparag 3y ago
  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.
eimrine 3y ago
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.
hn8305823 3y ago
> 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.
- jakear 3y ago
  Does the precise line dividing "bright but just barely not saturated" from "bright and saturated" actually matter?
  - adhesive_wombat 3y ago
    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.

asdfman123 3y ago

An mspaint.exe adjustment

jakear 3y ago

What's odd is even when downloading the full res image, the central colors are decidedly not all #000. There is a faint yet distinct radial gradient. It does not appear to be a compression artifact (format is png anyways).

friendlyasparag 3y ago
images released to the press sometimes get another, um, aesthetic pass. I bet if you could get ahold of the actual image file it would have the proper sentinel sentinel value (if they're still using fits files it'd be something ridiculous like -9999.)

sbierwagen 3y ago

To be clear, they were using the coronagraph: https://arxiv.org/pdf/2305.03789.pdf https://arxiv.org/pdf/2305.03789.pdf >The 23.0 µm coronagraph of MIRI uses a classic Lyot mask to achieve high contrast imaging near bright sources. The mask is rather large, providing an inner working angle (IWA) of ∼ 3.3λ/D, i.e., ∼ 2. Our data is the first complete reference PSF subtracted set of observations taken with JWST using this mode. There's some residual light and diffraction effects around the Lyot mask which they have manually deleted.

hn8305823 3y ago
Some images used a mask and some did not. The 25.5 micron image at the top of the article is one that did not use a mask.

geokon 3y ago

Any idea why it's not a perfect circle? Aberration in focus? And would that be pretty much equivalent to the true size of the star's corona? (seems huge..)