### Floodfill algorithm improvements

• To improve our algorithm we defined a star to be anything above 5 pixels in size.
• It seems that all hot pixels were removed:

• Found an interesting structure:
• To improve center founding, we found x and y weighted averages, such that:
• where and are the x,y centers and and are the x and y coordinates of the individual pixels of the star and is the pixel value of the pixel, and is the total number of pixels of a given star.
• An example of a found star center is shown below:
• The standard deviations were found using the following equations:

• where and are the standard deviations in x and y.
• Some information about found sigmas for all stars in this image:
 Minimum value Maximum Value Average Value 0.58 4.96 2.42 0.44 4.34 2.24

### A different way to estimate the mode

• Building on what we did last week, instead of just splitting the image array into 4 separate arrays and finding the mode in each new array, we allowed for an arbitrary number of arrays that the main array can be split into.
• A 2 by 2 splitting would be the following:
• If one splits the main image into as many arrays as there are elements in the original image, one would expect to get the original image back. This can be seen below:
• Below are more examples:

• If one takes a single mode over the entire image:

### 2D Fourier Transforms

• Fourier transforms of such a star field will give regions in k space for both background and stars.
• One of these can then be removed, leaving just stars or the background upon inverse Fourier transforming.
• Initial attempts of this can be seen below.

• This shows a location 1 image, with its background now clustered around the edges.
• This shows an attempt at removing the background from the image.
• This shows an attempt at removing the stars from the image. Note the image is logged, in order to better see the remnants of the stars.

-- ElenaCukanovaite - 01 Dec 2015

Topic attachments
I Attachment Action Size Date Who Comment
png 17_by_17.png manage 50.6 K 01 Dec 2015 - 22:46 ElenaCukanovaite
png 1_by_1.png manage 48.7 K 01 Dec 2015 - 22:47 ElenaCukanovaite
png 30_by_30.png manage 52.9 K 01 Dec 2015 - 22:45 ElenaCukanovaite
png 85_by_85.png manage 63.8 K 01 Dec 2015 - 22:44 ElenaCukanovaite
png FT_Loc1_nocut.png manage 1203.7 K 01 Dec 2015 - 16:33 DavidHadden
png Floodfill_original.png manage 87.8 K 01 Dec 2015 - 11:47 DavidHadden
png IFT_Loc1_bkgcut.png manage 49.6 K 01 Dec 2015 - 16:33 DavidHadden
png IFT_Loc1_starcut.png manage 1317.4 K 01 Dec 2015 - 16:33 DavidHadden
png Stacking_ap_6.png manage 42.2 K 01 Dec 2015 - 17:09 DavidHadden
png center_improved.png manage 68.5 K 01 Dec 2015 - 13:34 ElenaCukanovaite
png floodfill_imrpoved.png manage 37.8 K 01 Dec 2015 - 13:14 ElenaCukanovaite
png full.png manage 45.7 K 01 Dec 2015 - 22:43 ElenaCukanovaite
png interesting_stars.png manage 62.2 K 01 Dec 2015 - 13:38 ElenaCukanovaite
png l1_quadrants_copy.png manage 969.8 K 01 Dec 2015 - 22:42 ElenaCukanovaite

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Topic revision: r9 - 02 Dec 2015 - DavidHadden

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