Jim Misti's Processing Paper

 As many imagers do, I spend a large amount of time in Photoshop on an image, but there are some important steps that are done prior to that.  I tend to think of Photoshop as a "final touchup" program, with the Luminance and RGB files I load into it already pretty close to what I want in the final image.  Here's my generic processing work-flow, with a few comments:

1) Calibrate images (Dark/Flat/Stack) - result is 4 files, one each for Luminance, Red, Green, and Blue
2) Deconvolve Luminance Image in CCDSharp
- CCDSharp is now freeware available from SBIG.  At your focal length, I'd suspect that a setting of 1 CCDSharp iteration would add just a bit of sharpness without creating artifacts or over-sharpened appearance.
3) Non-linear stretch of Luminance image
- Use something like DDP in MaxIm, with User Kernel set to all zeros except for a central "1"
- Set the background level to a value just below the darkest values in the image
- After the DDP, adjust the display range from 0 to 65535 to see the full range of the image
- Keep trying different settings for the DDP until you are satisfied that the full tonal range of the object is visible.
- I find it nearly impossible to achieve the same results with Photoshop's Levels and Curves as I get with a non-linear stretch.
4) Color combine R/G/B files into TIFF
- If you're lucky, you will find a color combine ratio for your camera/filter combination that you can use from image to image.  If the color looks off after the color combine, however, it's better to try to get it close at this stage than to adjust it in Photoshop. Again, Photoshop might be fine for a final tweak of color balance, but the colors should be close going in.
5) Load Luminance into Photoshop
- If the image has a noisy background (almost always does), I do a Gaussian Blur using a masked layer, where I use an inverted copy of the image as the mask.  (Shorthand recipe: Copy L frame, Paste it on itself, Invoke a Layer Mask, Paste the L frame into the Layer mask, Invert the Layer Mask, Use Levels to darken the layer mask, select the top layer L image, do a Gaussian Blur with a low number - 1 to 3, Flatten the layers - this blurs the background but doesn't affect the higher signal areas)
6) Load RGB into Photoshop
- Levels and Curves to bring up color brightness
7) Combine L with RGB
8) All the tricks you know in Photoshop for "finishing touches"
- too many to list, but Scott Ireland's new "Photoshop Astronomy" is an excellent resource, as is Jerry Lodriguss' "Photoshop for Astrophotographers."  It was definitely Jerry's cyber-book that first showed me how to harness the power of Photoshop...

- Jim Misti