Interesting read on astrophotography processing

[Mac]

http://www.deseretnews.com/blog/47/10008839/Nightly-News-Astronomy-blog-Manipulating-Astronomical-Photos.html

[PhilB]

Very thought provoking. This is something that seems to apply to photography generally, articles on high dynamic range imaging popping up from time to time in photographic magazines. Perhaps you can argue that something that enables you to view all the data in an easily digestible form is to be encouraged? One thing that the writer does not seem to allow for is frequency shift. Most CCD cameras will record data into the infra red for example. Is an infra red image wrong just because you cannot see at this wavelength?

[Mike]

All astrophotography is artistic licence anyway. None of these objects would look like they are in photos even if you were very close to them. The very fact we use long exposures immediately makes it a false image as our eyes have no way of doing that naturally. If you were only 1/1000000 of the distance we are from these objects they would still be just as faint.

[MarkS]

The example he gives - dimly lit person on pavement with glaring car headlamps - is an interesting one.  The problem is not in acquiring the image - a CCD could have enough dynamic range to capture both.  The problem is in the display medium.  One could imagine a display device that accurately shows each level of brightness.  But when using such a display, just like viewing the original scene, the viewer would need to shield their eyes from the brightness of the car headlamps in order to view the dimly lit person.

But the display devices we use do not have such a wide dynamic range, so some compromise must be made when preparing the image for display.

[Rick]

The first time I saw an unsharp-masked photograph of M42 my impression was that it was much nearer what I'd seen through a telescope than any previous photographs I'd seen, especially in the whispy structural details (though not, of course, in the colours, as the human eye doesn't see colours well when the light intensity's low).