One of the problems with astro-images is that the printed photo can never fully reproduce the gamut of a computer screen. A screen uses trasmitted light, while a photo reflects light. They will never match exactly, and a screen will have a greater range of brightness than a printed photo. Because of this, printed images gain contrast (the darks get darker and the lights get lighter).*
Preparing astro-photos for printing requires some additional processing to more closely match what is seen on the screen. In theory, this process is straight forward, but in actual practice it is very difficult to print exactly what is seen on the computer. Each printer/computer combination is unique and will require trial and error until the best result is achieved.
The following are some guidelines for photo preparation for printing:
1. Lighten the image, especially the background, by 20-30%
2. Reduce the contrast
3. Leave plenty of room on the top end of the histogram so the bright areas don't get "blown out"
4. Option 1: Brightness/Contrast Adjustments
-Increase the brightness by 20-30%, use a layer mask to partially hide the image object in order to only increase the background brightness
-Decrease the contrast by 20-30%
5. Option 2: Shadows/Hightlights Adjustments
In Photoshop, the "Shadows/Highlights" filter is one of the best ways of boosting the background and reducing the contrast without adding extra noise to the image. As a starting point, set the "Shadows" amount to 20%, tonal width to 50% and a radius of 30 px. Set the "Highlights" to 100%, tonal width to 30% and a radius of 30 px. Set the "Color Correction to +20" and experiment with the "Midtone Contrast" slider to see the effect
6. Make sure that your image processing program is controlling the color profile during printing. Do not let your pinter control the color profile
7. It may be necessary to boost (or reduce in some cases) the color saturation of the image
8. Digital Download images are embedded with the sRGB color space, so use that when printing (not Adobe RGB for example)
*Credit: Chuck Reese