The ABCs of Image Processing Don Goldman Astrodon Imaging
Workshop Expectations • • • • •
We only have 60 min! Astrophotography is Technical Art not science What this workshop is You will get this PowerPoint file – relax! Some detailed DVD Tutorials: – – – –
Adam Block http://www.caelumobservatory.com/video/dvdpscs3.shtml Tony Hallas http://www.astrophoto.com/ezccd.htm Warren Keller http://www.ip4ap.com/ Web sites (Rob Gendler, Ken Crawford, Neil Fleming)
What This Workshop Is • Overview due to time • Intended for beginner to intermediate levels • Show processing workflow – Calibration, registration, data rejection, combining – Curves, color saturation, L + RGB
• Primarily use CCDStack, Photoshop • Fixing common problems in Photoshop – – – –
Gradients Oblong stars Noise reduction Star reduction/fixes
Topics • • • •
Detail vs Color (L + RGB) White point balance in astrophotography G2V Star white point Initial processing – Calibration, registration, data reject, combining, deconvolution – Color combine of RGB
• Final processing – Curves, Color saturation, Adding luminance – Sharpening coarse/fine detail – Fixing problems (star elongation, gradient, etc.)
Monochrome CCD Thinking • Different way of thinking from DSLR or OSC • Take hi-res luminance (colorless filter) – Unbinned (use all pixels) – 2-4 hours of 10 - 15 minute exposures – Select exposure time to make sure galaxy cores are not saturated
• Take low-res chrominance (RGB filters) – Binned 2 (4 pixels in a square makes one data point) – Acquire data faster – 30 min to 1 hour hour total from 5-10 minute RGB exposures
• Why?
Color and Detail Perception • • • • •
Our brains are wired to detect detail Less so, with color Colorize hi-res detail with lower-res color L + RGB = LRGB (Dr. K. Okano) Often done in layers in Photoshop
Example: Centaurus A Luminance Layer • Hi-res • Luminosity Blending Mode • Layer on top
Let the RGB colorize the higher res luminance
Chrominance (RGB) Layer • Lower-res • Layer on bottom
Centaurus A
White Point Balance
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DSLRs have white point (WP) options Makes a white light source white We need one too! We define sunlight as white We use a sun-like star (G2V classification) Makes sun-like stars in our images white
Where Are G2V Stars? • Download G2V database at http://www.astrodon.com/products/filters/e-series/
• Add G2V database to TheSky6 • Select G2V star, slew and center
How To Measure G2V RGB Weights
Remember: This is a system property of telescope, filters, detector, and the elevation of your target in the sky
Calibration and Pre-Processing • • • • • • • •
Check for bad frames Calibrate Register Normalize Reject bad data Combine DDP Save for Photoshop
Check For Bad Data • Cycle through each stack before calibrating • Exclude bad data
Calibration • • • • • •
Darks taken for the same exposure as lights Biases (zero-time darks) for base noise level Flats to flatten out light fall-off and eliminate dust donuts Make sure binning is the same Make sure CCD temperature is the same For best results, make sure you dither your exposures for easy elimination of hot pixels
Registration • •
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Aligns all stars so that they superimpose Afterwards, double-click on a star to see FWHM (in pixels) in all frames Multiply by plate scale to get FWHM in arcsec Exclude or de-weight bad data
CCDInspector Plug-In for CCDStack V2 $89.95 http://www.ccdware.com/buy/
Normalization • •
Takes out the effect of different brightness scaling Applies weights to each exposure
Data Rejection •
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Use Sigma with 8-10 or more frames, or Poisson with less Make sure hot pixels and other artifacts (satellite tracks) are selected red Zoom in and blink through images Set % to higher number to reject more With Data Reject window still visible, combine
Combine • Use mean combine (sum / # exposures) • Must have good rejection • If artifacts remain, consider median combine as a last resort • Save as 32-bit FITS (unscaled – no DDP) • Repeat for Luminance, Red and Green
The Masters (no, not Golf)
Final LRGB Registration • • • •
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Open L, R, G, B master combined frames Select L as the reference Repeat registration as before If your RGB data are binned 2x2, by selecting LUM will upsize them to 1x1 to match LUM Double click on star and check FWHM Deconvolute R, G or B to make similar FWHM Save All with REG appended to filename
RGB Color Combine • •
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Open R,G,B masters Combine color using G2V weights Neutralize background DDP stretch Save as 16-Bit TIF for Photoshop
Luminance Deconvolution • • •
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Needs some sharpening Smaller stars Double click on reference star for FWHM Decon entire image 60-80 iterations Compare FWHM Check for star damage Can do additional decon on just the galaxy
Luminance DDP • • • • • • • •
Same as RGB Lower Maximum Check DDP Adjust DDP slider left Decrease Gamma Readjust DDP slider left Brighten background Save as 16-BIT TIF
On To Photoshop
Yippee!!
Photoshop Processing • • • • • • •
Brighten faint objects Sharpen with high pass filtering Increase color saturation Combine L + RGB Further enhance color Crop Save for printing or internet posting
Luminance - Brighten Faint Stuff • • • • • • • •
Do work on duplicate layers Make sure histogram not clipped Brighten faint objects Lasso areas Feather Minor curves Collapse layers (CTL+Shift+E) Save versions as you go
Luminance – Fine High-Pass Filtering • • • • • •
Duplicate layer Select HP filter for 5-8 pixels Change mode to overlay Add hide-all layer mask Gaussian blur the layer mask Use paint brush and proper size to enhance fine detail, like dust lanes, HII regions
Luminance - Coarse High Pass Filtering • • • • • • •
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Enhance 3D effect Bring out spiral arms Same as before Use ~ 40 pixels Use larger paint brush Turn on fine high pass layer Adjust opacities to control strength of high pass Flatten Rename file
Color •
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Goal is to saturate color but not bring in noise Duplicate layer Curves, Levels Hue/Saturation (?) Match Color Check out the newer Vibrance tool Optional - Select galaxy, feather, match color Look for similar R,G,B histograms Here, extend B Adjust G Save adjusted file
Another Way - PixInsight • • • •
Excellent color saturation Curves transformation Use S Adjust B to balance histograms
http://pixinsight.com/ $233
Making the LRGB in Photoshop • •
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RGB base layer Go to Luminance image and CTL+A, CTL+C to copy Paste over RGB layer Lum on top Blending mode to Luminosity Adjust opacity to 5070%
Little Trick for Deeper Color Contrast • • • • •
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Duplicate RGB layer Put on top of Luminance layer Blending style to soft light Opacity to 1520% Increase opacity of Luminance layer to bring back faint areas Go back and forth to optimize Can use masks Save as a 3-layer PSD file Then duplicate and flatten
Final Cropping • • • •
End of process Crop out bad edges from registrations Flatten Save as hi-res TIF, 300 dpi, 16 bit
Posting • • • • •
Convert to 8-bit Resize Change profile to sRGB Save as jpeg Post that image!
Fixing Problems • • • • • •
Background color noise Halo reduction Oblong stars Gradients Smaller stars Star repair
Reducing Background Noise Carboni Actions
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Astronomy Tools (Actions) Developed by Noel Carboni Run action “space noise reduction” CTL+Z to add new results layer Repeat if necessary
http://www.prodigitalsoftware.com/Astronomy _Tools_For_Full_Version.html $21.95
Reducing Background Noise Plug-In Filters •
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• http://www.imagenomic.com/ NoiseWare Pro $69.95 • http://www.picturecode.com/ Noise Ninja $79.95
Imagenomic NoiseWare Pro PictureCode Noise Ninja Great selectivity for different types of noise Can use layer masks to control noise reduction Don’t oversmooth
Reducing Halos – Replace Color • • • • •
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Duplicate layer Circular marquee Large feather Replace color Eyedropper to select halo with fuzziness Select replacement color from background (eyedropper) Adjust fuzziness and lightness Adjust layer opacity to liking Flatten, save
Fixing Oblong Stars – Offset/Darken • Camera tilted to optical axis • Poor periodic error correction (PEC)
Gradient Removal - GradXTerminator Procedure 1.
Duplicate layer
2.
Magic wand – select background but not stars. See “marching ants”
3.
Shift + Magic Wand to add background for areas missed
4.
Alt + Lasso to draw additional areas not to be included in gradient removal, such as outer galactic arms
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Apply GradXTerminator with fine/fine and “neutralize background”
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CTRL + D to delete selection
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If acceptable, delete lower (original) layer and save layer with gradient removed
http://www.rcastro.com/resources/GradientXT erminator/ $49.95
Making Stars Smaller - Liquify • • • • • • • • •
Use new liquify filter in CS4/5 Works on individual stars Can be done in 16-bit Largest stars convey greatest impression Work on a dozen or so of those Duplicate layer Size brush over star and just click Star becomes smaller Hide/show layer to see if you missed any importants stars
Making Stars Smaller (Carboni) • • • •
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Liquify is selective This action affects ALL stars Can be done in 16-bit CTL+Z after action to put results in a new layer Turn off/on new layer to see effect Combine Carboni + Liquify
Making Stars Smaller - Pinch • • • • • • • • • • •
Only works in 8-bit Save for last Duplicate layer Circular marquee Filter/Distort/Pinch Set to ~50 Move marquee to new star Resize if necessary CTL-F to repeat pinch Set opacity of duplicate layer to blend in effect Flatten, save
Star Repair • • • • • • • •
Duplicate layer Circular marquee around star Copy/paste (becomes new layer) Edit/Transform/18 0 deg Change opacity to 80% to see both Superimpose Opacity back to 100% Erasure brush
Concluding Remarks • • • • • • •
Very demanding hobby Very rewarding hobby Remember – It’s technical art Develop your own style as an artist Use layers and save your work as you go Take home 15%? Use the internet to get nearly instant answers – http://tech.groups.yahoo.com/group/ccd-newastro/
• HAVE FUN! It’s a HOBBY!
Clear Skies