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Image Processing Tutorial

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

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Image Processing Tutorial

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  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 removalatthis 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’tdebloombecause 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 • CCDIS Plugin for CCDSTACK • http://www.ccdware.com/buy/

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