Cloudy nights, busy days.
I reprocessed the Eagle Nebula using Astronomy Tools in Photoshop after first summing 17 45-second exposures. Previously I had gone through a great deal of effort to get this result:
This time around I did things a little differently, and processed the channels separately, taking each channel and multiplying it by itself in Photoshop, twice. I removed much of the background using Astronomy Tools, and then scaled the image to 50% of the original so it would fit here….
The technique of multiplying the image by itself appears to be most useful in bringing out detail when the contrast of the image is very low. I tried the same technique on a higher contrast image – M57 – and was very disappointed in the results as the increase in contrast was so great that lower contrast parts of the image were effectively wiped out. This should be an artifact of Photoshop and the way it handles the multplication. More investigation is required, but I suspect that when 16-bit numbers are multiplied to give 32-bit numbers, only the upper 16 are retained in creating the new image. Another possibility is that the image is re-calculated as a 32-bit image, the upper bound is found, and then the image is adjusted so as to retain the most significant 16-bits of the highest pixel value. In that case, a saturated star will dominate the result, so that the stretched image loses lower light levels.
One thing to point out — the Eagle Nebula, strictly speaking, is the loose cluster of stars in the upper portion of the image and is also known as M16. Visually there is only a hint of the underlying nebulosity in the FLT-110, and from the city it is pretty much non-existent. The red nebula which is associated with M16 and seen here is IC4703 and only shows up in images, though in larger scopes it should be more apparent. The dark lanes in the nebula have been imaged at far greater resolution by the Hubble Telescope – look for images of the “Pillars of Creation” for more.