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Re: [APML] How dark should the background sky be?
>A question I have relates to the "best" luminescence of the background >sky. In order to bring out faint nebulosity, the overall brightness of the >image is enhanced, which means the background sky becomes paler >as well.
This is not always true. We can enhance selectively some regions of the picture. For example, if you use curves, the sky background can remain at the same value, but you can increase the contrast between it and the faintest features. Also there are nonlinear methods, like SMI or PIP that preserves the brightness of highlights and can be combined with curves to increase the contrast only where you want.
>I was wondering whether there was any standard used by members that >defines how dark they would like the sky as a function of not >compromising the fainter portions of nebulae and the fringes of galaxies, >etc. Thanks,
Usually that compromise is not an issue for me. I only care about the noise of the image and if what I can extract from the faintest regions are real features or not (natural sky variations, or noise). Another good point is the natural look of the image. Sometimes we can increase a lot the contrast between features and the background, but it does not looks pleasant, it feels like a bad paint...
BTW, ussually I set the sky backgroung to be neutral, with a slighty blue cast. The values are near 25, 27, 30 (RGB), but I really don't care for "exact values", so it may vary in luminance intensities a bit between each image.
Regards,
Carlos Milovic F.
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Astro & Photo - CMF
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Visita "AstroFoto", el foro de astrofotografía en español
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