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Real or fantasy ??
On Mon, 01 Sep 2003 17:47:04 +0200, Marco A. wrote:
Hello from Marco from Italy. I'm a newbye in digital elaboration. Often we can see in web pictures with a lot of small detail (0,5'' or smaller). My question is this: how can I know if a detail is 'real' or it depend only from digital elaboration? Ok, I can compare the image with an Hst picture. But does exist a method that tell me if my elaboration does not generate 'unreal details' ?? The kind of processing required to bring out details always introduces artifacts. The best solution to understanding and detecting them is to take lots of images as the planet moves. Actual structures will usually be apparent. Also comparing your images to those made by others is a good test. I don't know of any good way to know for sure what's an artifact, but any frequency components higher than the best PSF your optics are capable of are certainly artifactual. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#2
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Real or fantasy ??
"Chris L Peterson" wrote in message ... On Mon, 01 Sep 2003 17:47:04 +0200, Marco A. wrote: Hello from Marco from Italy. I'm a newbye in digital elaboration. Often we can see in web pictures with a lot of small detail (0,5'' or smaller). My question is this: how can I know if a detail is 'real' or it depend only from digital elaboration? Ok, I can compare the image with an Hst picture. But does exist a method that tell me if my elaboration does not generate 'unreal details' ?? The kind of processing required to bring out details always introduces artifacts. The best solution to understanding and detecting them is to take lots of images as the planet moves. Actual structures will usually be apparent. Also comparing your images to those made by others is a good test. I don't know of any good way to know for sure what's an artifact, but any frequency components higher than the best PSF your optics are capable of are certainly artifactual. One thing that is well worth looking for, are artefacts on 'known' edges. On Mars images for instance, the edge of the planet is about the sharpest contrast contour present. If you look at some of the posted images, you will see a second 'ghost' ring, following this edge, sometimes on the dark sky, and sometimes on the lighter surface of the planet (depending on the particular processing used). This is in a sense, a 'sure sign' of everprocessing. A high frequency filter has been applied, to the point where the sharp edge is creating overshoot, and producing these artefacts. Compare these images with others, where this type of artefact is not present, and you will see that the latter tend to have a 'softer' look, with some of the sharp edges missing, but you can be far more confident that the latter's details are more likely to be real... Best Wishes |
#3
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Real or fantasy ??
On Tue, 2 Sep 2003 12:10:31 +0100, "Roger Hamlett"
wrote: One thing that is well worth looking for, are artefacts on 'known' edges. On Mars images for instance, the edge of the planet is about the sharpest contrast contour present. If you look at some of the posted images, you will see a second 'ghost' ring, following this edge, sometimes on the dark sky, and sometimes on the lighter surface of the planet (depending on the particular processing used). This is in a sense, a 'sure sign' of everprocessing. A high frequency filter has been applied, to the point where the sharp edge is creating overshoot, and producing these artefacts... It is worth emphasizing that there is nothing necessarily wrong with "overprocessing" and the creation of artifacts. You see it all the time in professional images. The processing required to bring out certain kinds of details will often generate artifacts elsewhere in the image. What's important is to recognize what's real and what's not, lest you fly off thinking you've discovered a Martian city or something g. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
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