Image backgrounds
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Can someone explain the different backgrounds seen in the images? The most common one is the grainy one. Then there is the rarer, pitch black one.
http://www.galaxyzoo.org/#/examine/AGZ00060mc
http://www.galaxyzoo.org/#/examine/AGZ00002kpPosted
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by
vrooje
admin, scientist
It's a bit difficult to compare these two since one is from the SDSS and the other is from HST, so the images were made from very different data.
Within each dataset, though, the images are tuned to show as many of the details of the central object as possible. The way the images are tuned can vary quite a bit given that we have such a range of galaxies, from the faint blobs to the huge and bright. For the faintest images, the signal is amplified somewhat and they thus look noisier than the brightest galaxies (and if there happens to be a bright source in those images, it often looks weird because it's saturated).
As you say, the pitch-black backgrounds are rare. Because we have hundreds of thousands of galaxies it wasn't possible to hand-tune the scaling for each object, so although we were very careful sometimes the algorithm does it slightly differently than we might have had we done it individually. But this is typically a small effect -- in the example above there's still enough detail to classify that galaxy.
Hope that helps!
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vrooje,
Are there documents/web-pages that explain these tunings and signal amplifications? I guess the the image is stored as info about the pixels (brightness, colour etc), right? Does the algorithm try to change these attributes?
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In the following image, is the brightness of the nucleus and that of the star below it a result of image processing?
http://www.galaxyzoo.org/#/examine/AGZ0001gxb
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