Many times when processing astrophotographs it is difficult to increase the brightness of the deep sky object without over brightening the stars. This results in bloated stars that detract from the overall appearance of the image. As with most of the other processing techniques covered here, your favorite layer capable image editor can help to alleviate the problem. The example below uses Paint Shop Pro, but the method works equally well in Photoshop or Gimp. First let's take a look at a stretched shot of the Witches Broom Nebula.
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As you can see, the multitude of bloated stars in the field greatly detract from the image and obscure much of the faint red nebulosity and this is after a pass of star shrink processing in an attempt to minimize the problem. Compare this with the same data where the stars were separated from the rest of image before a stretch was applied to the nebula.
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The results show much more of the faint red nebulosity throughout the image as it is no longer overwelmed by large bloated stars. The algorithm is somewhat convoluted but fairly simple to implement using any layer capable image processor that supports the difference and lighten blend modes.
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Now for the fun part
Now you can process each layer in what ever way you like to produce the result you are after. When you are done, switch the combine mode of the layer containing the stars to lighten and flatten the layer stack. |