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Image Processing Tutorial

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Presentation on theme: "Image Processing Tutorial"— Presentation transcript:

1 Image Processing Tutorial
Bernard Miller

2 CCDStack Work Flow Create Master Dark, Bias, and Flat Calibrate
Hot/Cold Pixel Rejection(Optional) Debloom (Optional) Register Normalize Data Reject Combine

3 CCDStack Work Flow Create Master Dark, Bias, and Flat
Bias: min/max clip (0,1) or (1,1) Dark: min/max clip 0-6 frames: (0,1) 7-15 frames: (0,2) 15+ frames: (1,2) Flat: Median

4 CCDStack Work Flow Calibrate Images Calibrate Rotate West Images
Hot/Cold Pixel Removal I only do hot pixel removal at this stage for RGB Luminance images I do not do hot pixel removal Hot Pixel Removal General Recommendation If dithered images and more than 7 subframes, don’t do hot/cold pixel removal If not dithered or 7 subframes or less, do hot/cold pixel removal Debloom I don’t debloom because I have deblooming camera

5 CCDStack Work Flow Registering (Stack->Register) General Luminance
Get the CCDIS alignment plugin After registering, double-click on small to medium star and arrange subframes by increasing FWHM Luminance Use “Nearest Neighbor” algorithm Assuming you have 8 or more subframes RGB Read in the Stacked Luminance image prior to registering Use “Bicubic B-Spline” algorithm If you have 8 or more subframes you can use try not using hot/cold pixel removal and using “Nearest Neighbor”

6 CCDStack Work Flow Normalizing (Stack->Normalize)
Use the subframe with the best FWHM as reference Always use Stack->Normalize->Control->Both First selection is the background Second selection is the signal or object For nebulas, look for dark region for background selection

7 CCDStack Work Flow Data Rejection (Stack-> Data Reject)
For 8 or more subframes, use “STD sigma reject” For less than 8 subframes, use “Poisson sigma reject” Use 2.2 for the “sigma multiplier” Red pixels go away if you close the dialog box, but the data is still there Combine (Stack->Combine->Mean) Save Calibrated and Stacked frames in separate directory

8 CCDStack Work Flow Deconvolution of Luminance Image
Process->Star Selection Max ADU: About half of your full ADU range (~30K for 16-bit camera) Threshold ADU: About 2000 for galaxies and images with dark background Above the ADU for faint part of nebula

9 CCDStack Work Flow Deconvolution of Luminance Image
Process->Deconvole Select “PSF to fit Moffat” Select “Positive Constraint” Matrix Radius About 2X your FWHM Sharpen Count Lower numbers do MORE sharpening I usually use 0-4 Bias subdivisions Lower values result is less star ringing I usually use about 1X my FWHM Create two deconvolved images Use iterations for one image Use for the other

10 CCDStack Work Flow Applying DDP and Saving Images
Should have original luminance and both deconvolved images Adjust original luminance image Window->Adjust Display Make sure DDP is selected Background slider adjusts background brightness DDP slider adjusts image brightness Gamma set to 0.90 Brightest part of image should be about 200 counts Not including saturated parts of image like galaxy cores Background should be between 20-30 Use Histogram window to make sure you are not clipping When finished with original image, click “apply to all” File->Save Scaled Data->This Save all three luminance images as 32-bit float and TIF

11 CCDStack Work Flow Missing Value Technique for Combining Images
Start with long exposure image selected Normalize the two images using the long exposure image as the master Select over exposed portion of long exposure Stack->Data Reject->Procedures->Reject range Reject pixels above about 2/3 of full range (~40K for 16-bit) Remember to select “Apply to this” Select Grow and use 3-5 pixels Select “Set Rejects to Missing Value” Click on “Weight” column of short exposure image Set to very small number (i.e. 1E-7) Select Stack->Combine->Mean

12 Recommended Plugins CCDStack CCDIS Plugin for CCDSTACK

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