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The "photo" of the black hole has been retouched!



 
 
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  #1  
Old April 15th 19, 11:57 AM posted to sci.astro
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Default The "photo" of the black hole has been retouched!

The original is on the screen of Katie Bouman's laptop:

https://sites.google.com/site/testso...ies/bouman.jpg

So there are other similar structures around the black hole formation. Either this makes the program or they actually exist. In the last case we would have several black holes.

Best regards

Walter
  #2  
Old April 17th 19, 09:21 PM posted to sci.astro
Steve Willner
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Default The "photo" of the black hole has been retouched!

In article ,
writes:
The original is on the screen of Katie Bouman's laptop:
https://sites.google.com/site/testso...ies/bouman.jpg

Why do you think a random image on a laptop is "the original" rather
than some work-in-progress image?

What do you even mean by "the original?" EHT made images on four
different days, each processed independently by four different teams.
Which is "the original?"

The paper at
https://iopscience.iop.org/article/1...41-8213/ab0e85
gives an _overview_ of the imaging process.

All the relevant papers are linked from
https://iopscience.iop.org/journal/2...e/Focus_on_EHT

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  #3  
Old April 18th 19, 08:03 AM posted to sci.astro
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Default The "photo" of the black hole has been retouched!

Am Mittwoch, 17. April 2019 22:21:47 UTC+2 schrieb Steve Willner:
In article ,
writes:
The original is on the screen of Katie Bouman's laptop:
https://sites.google.com/site/testso...ies/bouman.jpg


Why do you think a random image on a laptop is "the original" rather
than some work-in-progress image?

What do you even mean by "the original?" EHT made images on four
different days, each processed independently by four different teams.
Which is "the original?"


Even in papers the images are already retouched. Compare the image on Katie Bouman's laptop and there left image from Paper

https://cdn.iopscience.com/images/20...b0e85f4_lr.jpg

Katie Bouman's image is sharper and includes more details.
  #4  
Old April 18th 19, 08:27 AM posted to sci.astro
Martin Brown[_3_]
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Default The "photo" of the black hole has been retouched!

On 18/04/2019 08:03, wrote:
Am Mittwoch, 17. April 2019 22:21:47 UTC+2 schrieb Steve Willner:
In article ,
writes:
The original is on the screen of Katie Bouman's laptop:
https://sites.google.com/site/testso...ies/bouman.jpg

Why do you think a random image on a laptop is "the original" rather
than some work-in-progress image?

What do you even mean by "the original?" EHT made images on four
different days, each processed independently by four different teams.
Which is "the original?"


Even in papers the images are already retouched. Compare the image on Katie Bouman's laptop and there left image from Paper

https://cdn.iopscience.com/images/20...b0e85f4_lr.jpg

Katie Bouman's image is sharper and includes more details.


They are not necessarily "details" so much as imaging artefacts that
haven't quite been fully calibrated out yet. There looks to still be a
faint copy of the ring structure displaced by half a diameter south to
me in that first version - though it clearly does show a main ring.

The choice of final detail shown is usually shown convolved with a
gaussian beamshape to be as conservative as possible. The raw beamshape
of a sparse interferometry synthesis map is truly horrible to look at.

The choice is pretty much to either have resolution that depends
strongly on local signal to noise (which experienced practitioners
sometimes prefer) or convolved to some nominal resolution like a normal
photographic image which is much easier for most people to understand.

I suggest you read the paper already referenced before making baseless
accusations against the researchers. They have done a very good job of
testing how robust their results are with partial data and individual
observing days taken in isolation. The ring stands.

https://iopscience.iop.org/article/1...41-8213/ab0e85

The only thing on her image that would have interested me is the single
bright blob at about 12 o'clock. Everything else looks like it is a
faint copy of the true image not quite aligned with the phase centre.

I'd have much preferred it if they had also made an image zoomed out by
10x or 100x (or whatever the isoplanatic patch will allow). I'd be very
interested to see the start of the jets in the field of view.

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Martin Brown
  #5  
Old April 18th 19, 10:55 AM posted to sci.astro
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Default The "photo" of the black hole has been retouched!

Am Donnerstag, 18. April 2019 09:27:08 UTC+2 schrieb Martin Brown:
On 18/04/2019 08:03, wrote:


Katie Bouman's image is sharper and includes more details.


They are not necessarily "details" so much as imaging artefacts that
haven't quite been fully calibrated out yet.


The image in Paper is more blurred and also darkened on the edge. The good word "Calibrate" I would not use for this kind of editing
  #6  
Old April 23rd 19, 12:30 PM posted to sci.astro
Martin Brown[_3_]
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Posts: 189
Default The "photo" of the black hole has been retouched!

On 18/04/2019 10:55, wrote:
Am Donnerstag, 18. April 2019 09:27:08 UTC+2 schrieb Martin Brown:
On 18/04/2019 08:03, wrote:


Katie Bouman's image is sharper and includes more details.


They are not necessarily "details" so much as imaging artefacts
that haven't quite been fully calibrated out yet.


The image in Paper is more blurred and also darkened on the edge.
The good word "Calibrate" I would not use for this kind of editing


But it is pretty much what happens when the phase calibration of VLBI
baseline data is fine tuned by self calibration on the initial result.
Basically you can use the known property of the sky brightness being
everywhere positive to detect and fix residual systematic errors.

A brief introduction to VLBI is online here.

http://www.phys.unm.edu/~gbtaylor/as.../vlbi_apr4.pdf

I would refer you to page 45 of it which shows the result of VLBI on a
fairly typical source without phase calibration, with first cut
reference only and then the final image after full self calibration.

Note that some of the junk on the intermediate image has coalesced into
real source structure and the resulting background is much flatter.

FWIW M87 jets observed by VLBI at 43GHz on a 10mas image size are on
page 11 although a nicer video at several epochs is online he

http://www.aoc.nrao.edu/~cwalker/M87...vies_only.html

--
Regards,
Martin Brown
 




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