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Image Processing Tutorial Bernard Miller. CCDStack Work Flow Create Master Dark, Bias, and Flat Calibrate Hot/Cold Pixel Rejection(Optional) Debloom (Optional)

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Presentation on theme: "Image Processing Tutorial Bernard Miller. CCDStack Work Flow Create Master Dark, Bias, and Flat Calibrate Hot/Cold Pixel Rejection(Optional) Debloom (Optional)"— 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 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 20-30 iterations for one image Use 150-200 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 – www.ccdware.com/products/ccdstack www.ccdware.com/products/ccdstack CCDIS Plugin for CCDSTACK – http://www.ccdware.com/buy/ http://www.ccdware.com/buy/


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