<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