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Originally Posted by irwjager
Steven,
I sent ESO a link to the image this morning and got a very nice reply just now from Lars Lindberg Christensen/ESO
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This is indeed a very interesting image you have made! And thanks for sending it! Your processing certainly brings out the galaxy much better.
There are however also some artifacts - see around the yellowish star to the right. It seems your algorithm brought out some stars that are not there, but are just noise features in the ghost around the star. Being a scientific institution we are forced to be a bit conservative with our processing. One of our main rules is that our images should always only show "real stuff", i.e. no artifacts like dark ringing around stars due to too much sharpening. It is however an ongoing discussion far we can push technology and still stay within our "moral limits". Thanks again for sending your image - very enlightening!
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The response is as I expected - the image as-is, is of little scientific value (and I must agree). However, I replied with a method that is similar and would allow for the specification of a confidence interval of the results, such as, for example, the popular 95% confidence interval often used in scientific research.
This method would concentrate on the density of distribution of small stars.
We would convolve just a single pixel per star, using a kernel radius that would result in a 5% energy per-pixel convolved result. We would then add this result to the image (e.g. 20 pixels in the immediate vicinity of the star would be brightened by 5%). As such, the 95% confidence interval requirement would be met (e.g at worst we would be adding 5% false signal to the image in case we erroneously selected a star/artefacts that wasn't supposed to be selected). Dense concentrations of small stars would cause a significant local brightening, causing a 'super structure' to emerge.
We can leave this super structure in the image, or we can leave out the super structure and measure the brightness of the super structure where small stars are located and brighten them accordingly.
Care must be taken to select only small stars. Care must also be taken to heal any parts of the image that are affected by big stars (and halos) in a way that does not upset local star density (e.g. these parts of the image need to be replaced by an approximation of small-star density), so that convolution of that area results in a neutral patch. Despite these 2 challenges I do believe this would be a viable approach.
Then again, I may have missed something (to be honest, probability theory isn't my strong point) and may just be full of it...  |
Ivo,
It's excellent you got a reply, even though I don't agree with it....
First of all with regards to scientific standards, the ESO image doesn't stand up either. As I mentioned previously their image is clipped, (resampling does give a "decent" histogram however). So they have lost quite a of bit detail in the galaxy.
Secondly on the question of artifacts, processing an already compressed processed JPEG image doesn't help.
A way of dealing with this issue and incorporating your own ideas is to process their raw FITS data.
I wonder if ESO would be obliging?
Regards
Steven