Found a site for raw Hubble/JWST images... Raises questions.

[pipnina]

I've always wondered why the RAW image files from these telescopes can be so hard to find, since they are not privately owned or operated but paid for with international tax money. But I found a website (most likely intended for researchers) that lets you view the various obsrvations with a variety of supporting and pre or post-calibrated files. You need to filter searches somewhat to find the observation code, then make a request for the date relating to those codes, then access it via FTP client... But I got some hubble raws of the crab nebula.

I now realise 2 things: The uncalibrated raws have HUGE artifacts. Bright stars bloom on spilling columns (I forget the name of the CCD effect), LOOOADS of cosmic ray strikes, and I think a nasty 45 degree angle square rounded filter silhouette!?

They provided various calibrations as well as other files I am not sure of the purpose of, but they don't match the source image's paramaters! Plus a final calibrated image has distortion relative to the RAW and also JPEG artifacts... And somehow a single fits is opening multiple image tabs in GIMP.

Example:

RAW (stretched and curves)

Calibrated

Some kind of cosmic ray / bad column mask?

No idea what these are!

 

I think it's fascinating to see what this telescope captures before human hands touch it, but I also find it very confusing from a "why is the camera's FOV not used properly / vignetted", "why a single 45 minute exposure instead of 9x5 min or 5x 9 min to remove cosmic rays?" or "why does their CCD bloom so harshly". Not to mention "why is it so hard to find these files to begin with!"

 

What do you guys think?

[Ags]

Always remember: this is an imaging rig designed by a government committee!

[markse68]

I ran into the blooming issue a while ago and couldn’t understand why they didn’t have anti bloom structures on their ccds like we do. Ultimately It’s a a scientific instrument with pretty pictures only a side line. 

“Anti-blooming structures - pros and cons

Some sensors are designed with structures built into them to limit blooming - anti-blooming structures. Anti-blooming structures bleed off any excess charge before they can overflow the pixel and thereby stop blooming. However, anti-blooming structures can reduce the effective quantum efficiency and introduce non linearity into the sensor. Therefore, anti-blooming sensors are not recommended for applications requiring very low light or high accuracy measurements.”

https://andor.oxinst.com/learning/view/article/ccd-blooming-and-anti-blooming

Mark

[Tomatobro]

There is a feature on this in the July 2021 Astronomy Now magazine.