Tyler has a really great point here and I don't think it is cheating to stretch the image to bring out details. I have sort of ambivalent feelings about it. It's a good thing to bring out aspects of galaxies, for example, that truly are present. But it gives a distorted view, a scene that is not visible in nature. A galaxy core that actually is many times brighter than the distant arms will not be relatively as bright in the stretched image. In that respect the image is not true to nature in all aspects -- it's something that bothers me. Maybe I'm too much a purist, but these are at least considerations to think about. I know Tyler is the master among us in astrophotography, and I appreciate his viewpoint. In fact, he's probably right. But I still have this nagging feeling. Thanks, Joe ________________________________ From: Tyler Allred <tylerallred@earthlink.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tue, March 30, 2010 11:16:16 AM Subject: Re: [Utah-astronomy] M-82 <Joe Bauman said... <Magnificent, Patrick! In response to your question, you need to mask and burn etc., to show the core details as well as the faint arms. But <in a way that's cheating. It's like a photo at night with a car's bright headlights shining at the photographer: you can print the negative <to show the general scene, people on the sidewalk, with washed-out blazing headlights or you can darken the whole scene and show the <headlights as sharp round orbs and the people hardly visible. But to show both you have to manipulate the image, "burning in" the headlights <with the enlarger or PhotoShop. That results in an unnatural view of the scene. You shouldn't have it both ways. I feel somewhat the same way <about manipulating astrophotos. The center is magnitudes brighter than the arms and a photo that in effect dims the center isn't a true <report. -- Joe Hello all. Joe brings up an interesting question, and I want to respond to this issue of whether or not it offers a "true report" if an image is stretched to show the full range of detail. The issue of stretching astronomical images often comes up and I hear the so-called purists argument that you shouldn't manipulate the data because it is somehow "cheating". I will try to debunk that argument now. Let me start by asking a question... Question: Why do scientists present data on non-linear plots (such as log-scale plots, probability plots, pie charts, etc.)? Answer... Because the real data often covers a range that is too wide to see and evaluate without manipulating the presentation of the data. So, is it "cheating" to show data on a log-scale or probability plot? Or for that matter, to plot log-transformed data? I think the answer you would get from scientists is universally a resounding "no". Is the presentation of data in astrophotos really any different? I think not. If you present the data without stretching, then real data is not even visible. That data represents real structures within an object. Is it a true report to allow real structures to remain unseen, simply because the range of data is too large to represent on a linear scale? Again, I think the answer is a resounding "no". I normally process my images by applying a log-log stretch to the linear data. That means that any value in the mostly linear representation of the data (directly off the chip) has a mathematical transformation applied that allows the full range of values to be better represented in the image. I rarely use the burn tool to alter my images. In fact, I do very little individual pixel manipulation, and most of what I do is removal of defects from hot pixels and dead pixels on the CCD, which I would not characterize as cheating. In my image processing, I try to show the variability in the actual data, and to accentuate the subtle details that allow the true structure of the object to be seen clearly by the viewer. I don't consider that to be cheating. In fact, I see it as quite the opposite... as revealing the true character and structure of the object. I thought I would offer these thoughts for anyone who is interested. Cheers, Tyler PS - Don't worry Joe... I am not upset, but rather I appreciated the chance to discuss this issue. :) ________________________________ From: Patrick Wiggins <paw@wirelessbeehive.com> To: utah astronomy utah astronomy listserve <utah-astronomy@mailman.xmission.com> Sent: Wed, March 24, 2010 4:02:38 AM Subject: [Utah-astronomy] M-82 I was between data taking projects tonight so I refocused the scope for the warmer temps that may finally be arriving. Once finished I shot five 30" test images of M-82 and stacked them. http://users.wirelessbeehive.com/~paw/temp/M82.JPG I'm satisfied with the focus and I like the spiral arms and the detail near the core but wish I knew how to keep the core itself from burning out. patrick _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.slas.us/gallery2/main.php Visit the Wiki: http://www.utahastronomy.com _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.slas.us/gallery2/main.php Visit the Wiki: http://www.utahastronomy.com _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.slas.us/gallery2/main.php Visit the Wiki: http://www.utahastronomy.com