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What is DDRA?

What is DDRA?. DDRA = Dirt Digger Running Average (for those hard to get out signals!) Purpose: When unable to lock on a target object in LiMovie , DDRA creates a new AVI with a higher S/N. When your time stamp is unreadable DDRA can provide a means of pulling the numbers out of the noise.

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What is DDRA?

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  1. What is DDRA? • DDRA = Dirt Digger Running Average (for those hard to get out signals!) • Purpose: • When unable to lock on a target object in LiMovie, DDRA creates a new AVI with a higher S/N. • When your time stamp is unreadable DDRA can provide a means of pulling the numbers out of the noise. • When all else fails to succeed in reducing your RAW AVI. • Method: • DDRA creates a running average by averaging individual fields, not just frames, thereby providing twice the data. • For instance a 3 frame running average will use 6 fields to average together, a 6 frame running average uses 12 fields, etc.. • It is possible with DDRA to create a 1 frame running average by simply taking the two fields of the same frame and averaging them together!

  2. Basic folder template for DDRA DDRA Step #1: Before beginning a DDRA run it is necessary to set up a file folder structure to organize all of the resulting images and AVIs that are going to be created. Using this template I can just copy and paste these folders into whatever main folder I am analyzing.

  3. DDRA Step #2 Take raw AVI and dissect NTSC interlaced frames into separate fields. fieldA fieldA fieldB fieldA Virtual Dub deinterlace Video filter fieldB RAW AVI fieldA fieldB fieldA fieldB fieldB

  4. VirtualDubDeinterlace Video Filter When you deinterlace a 640 x 480 NTSC video frame you get two fields that are 640 x 240. To get two resulting deinterlaced fields that are 640 x 480 all you have to do is select “Duplicated field X” in the Deinterlace Dialogue box.

  5. Virtual Dub: Export Image Sequence After you have set up the deinterlace video filter you then export the sequence of fields into a folder in the directory you are working on. It is important to export as BMP, because that is what format ImageJ will need to work with.

  6. DDRA Step #3 • Launch ImageJ and initiate the DDRA macro/pluggin • Follow the menu commands that tells the macro where all the associated directories are to find the fields, where to put the newly created image sequence, and what name and where to place the resulting AVI. • Prior to saving the new AVI, DDRA will convert the image sequence to an 8-bit greyscale shrinking the file size by a factor of 3!

  7. Open your new AVI and reduce in LiMovie

  8. Occular 3.14 analysis of the LiMovie CSV

  9. LiMovie CSVs for Testing DDRA Taking my 20080712 (892) Seeligeria occultation I created a CSV file for: • RAW (control) AVI of the occultation • 1 frame (2 field) DDRA AVI • 2 frame (4 field) DDRA AVI • 3 frame (6 field) DDRA AVI • 15 frame (30 field) DDRA AVI • 30 frame (a whopping 60 field) DDRA AVI

  10. LiMovie CSVs Used for Testing Occular I created a series of CSV files where I increased the measurement aperture in LiMovie to purposely introduce noise into the signal: • RAW (control AVI) CSV using 4 pixel radius measurement aperture. The S/N = 1.26 • 5, 6, 7, 8, 9, 10, 11, and 15 pixel radius aperture decreasing the S/N to 1.17, 1.11, 1.01, 0.89, 0.81, 0.75, 0.69, and 0.5 respectively

  11. Conclusions: • A minimal DDRA running average of 15 frames or less provides the exact same resulting times within the Occular error bars, showing DDRA does not skew results. • Occular’s superb statistical analysis can find the true event even with S/N much less than 1.0! • A minimal running frame average provides the same time resolution as a RAW AVI because the time interval between averaged frames is still 33.3ms. • Conclusion #3 gives rise to the possibility that an improved version of DDRA could be written that provides a running FIELD average, reducing the interval between data points to 16.7ms! Stay tuned for those tests…

  12. LiMovie showing the absurdly large 10 pixel radius aperture

  13. John Grismore’s 20080826 (94) Aurora AVI RAW AVI, KIWI time stamp illegible 6 frame DDRA renders time stamp and target star more visible

  14. Extracting time using LiMovie and 6 frame DDRA Being unable to read the time stamp in the noise of this original RAW AVI, I created a 6 frame running average that then made the KIWI time stamp legible. It was, of course, blurred due to the averaging of frames. However putting the measurement aperture in LiMovie over the “0” in “40” and using the “Avoid sunlit Face” feature to avoid the “4” I was able to measure the transition from “9” to “0” to “1” (39, 40, 41 seconds). The center frame of this dip (242) represents the center of the 40 seconds time period, i.e. 40.500 (approximately).

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