Re: [APML] OT: DSS image processed: Barnard 142/143 Complex ("E"Nebula)

[Ray Butler <ray.butler@nuigalway.ie>]

 > Vicent Peris has processed one square degree of DSS data for the B 142
 > region, AKA the "E" nebula.
 > See it at:
 >
 > http://pleiades-astrophoto.com/pixinsight/DSS_Gallery/index.html
 >
 > I think Vicent's results are very impressive. Hope you like it too.

It's impressive, and a great illustration of the functionality of the 
software...but as an aesthetic observation, maybe it's been 
over-smoothed in the wavelets/noise reduction department? It reminds me 
of "space-art", painted with an airbrush...to me it just lacks reality, 
somehow.

There's a story, which this image inspires me to tell. A few years ago, 
I assisted a pilot research program of employing deconvolution and 
wavelet-based noise reduction on digital mammography x-ray images. We 
processed the images to "improve" them to our eyes, and spent a long 
time optimising this. But the litmus test was a set of clinical trials 
with radiologists at University College Hospital, Galway. The 
radiologists evaluated the test images under various headings. The tests 
were blind (the "before" and "after" images were presented randomly), 
and our team repeated them several weeks later to check for internal 
consistency (radiologists have excellent memories for image details: you 
have to allow a long time to pass before presenting them with the same 
set of data again, as otherwise they'll just remember their previous 
judgements).

The upshot of all this was that what _we_ considered to be better images 
(with rather aggressive processing) was not what _they_ considered to be 
better. They were accustomed to seeing certain levels of noise, grain 
and high-frequency artefacts, and our first, over-processed versions 
threw them. They felt less secure in evaluating the possible presence of 
dangerous micro-calcifications, or whatever. So we scaled back our 
processing to a level that they were much happier with, and then there 
were genuine statistical improvements in their clinical diagnoses.

The moral of the story? I think it might be that if one presents an 
over-processed astrophoto to someone who is very used to looking at 
astronomical photos/images, it will provoke an uncertain reaction. If 
one presents it to Joe Public, he'll probably think it is beautiful and 
admire its smooth noiselessness. There are cases when there is no option 
but to produce images which have that "airbrushed" look - it can be the 
only way to produce an acceptable image in the photon-starved X-ray 
domain, for example the Chandra satellite's images. But in the optical 
domain, it's really not my preference; when the processing is obvious 
and holds the eye's attention, it looks somewhat unnatural. The trick to 
image processing is to make the viewer think that there was no 
processing. It's really hard to do this, of course.

Ray "who finds image noise familiar, maybe even comforting" Butler

> 
> Regards,
> 
> Juan
> ___________________________________________________________
> 
> Juan Conejero, Pleiades Astrophoto Team
> juan.conejero__at__pleiades-astrophoto.com
> PixInsight Home Page: http://pleiades-astrophoto.com/pixinsight/
> ___________________________________________________________
> 
> 
> _______________________________________________
> Astro-Photo mailing list
> Astro-Photo@seds.org
> http://seds.org/mailman/listinfo/astro-photo

-- 
Dr. Ray Butler (ray.butler@nuigalway.ie || ray@physics.nuigalway.ie)
Lecturer, Dept. of Physics || Computational Astrophysics Laboratory
National University of Ireland, Galway, University Road, Galway, Ireland.
Tel: +353-91-524411 ext. 3788   FAX: +353-91-525700

_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo