|Sometimes, for what ever reason, you can't get enough exposure to make an image as clean as you would like. In my case it is usually lack of patience as I don't get nearly enough time under a dark sky so I try to capture as many objects per night as I can. Never throw those less than perfect images away as most times a little (OK maybe a lot) of time spent processing can turn a so so image into one you can be proud of. The following image of M16 is a good example. It is a 15 minute exposure of three, five minute sub-frames. Noise is quite evident and the image had to be stretched to the point where the stars were very bloated. A little processing saved the image and produced the M16 shot shown below. Click on the image to see the original version.|
|The processing starts with
the noisy image and the stars were separated
out on another layer. The stars were then passed through an
erosion filter to reduce the bloat and some of the larger ones were
selected and given additional passes through the erosion filter. Once
that was done agressive, masked, noise
reduction was applied to the deep sky layer. With the noise
now under control, the background
was corrected leaving a nice flat sky background.
Some careful curves adjustments were applied to enhance the nebula. The
curves adjustment function in Paint Shop Pro allows individual control
over each colour channel so both the red and blue channels were very
to give the sky a slight blue tint and to improve the faint red
emission areas of the nebula. Finally some star
trailing was removed and the star layer was recombined with
the deep sky layer to create the final image.
Both of the images are from the same data set. In fact, the fully processed version was made from the noisy image and not from the the original raw camera data.