Mode vs. Median Background

• The problem with using the mode is that if a number does not appear more than once then the mode just takes the first number in the list.
• Therefore, a median seems more practical.
• Below is the mode and median background for splitting of 30x30 and 15x15:

• Because of the reason outlined above we shall use median instead of mode.

Generated star field

• From simple curve_fit fitting we sampled the parameters , , and for the Gaussian for each randomly positioned star:
• Generated 50 stars.
• For each randomly generated star position, a Gaussian was generated with the given centers and randomly choisen parameters from fitting images of Location 1 in focus filter (exposure time: 10 seconds).
• The resulting Gaussian for one star was calculated over the entire image. This was done for all the stars.
• Each pixel was then treated such that its pixel value up to this point was taken as the mean of a Poissonian distribution. A random Poissonian variables was then generated with that mean and this was set as the pixel value for each given pixels.
• The resulting field and its background:
• When run through our floodfill algorithm and it found 47 stars. Following stars were found:
• It removed well shaped stars but left some stars that resemble galaxies. Must fix this.
• Width ratios shown below and calculated using:

• The distances between found centers and generated centers is shown below:
• Largest distance is due to the following star:
• Disrepancy is due to neighbouring star.

Skeweness of data

• Last week we saw that the brightest star appeared to be skewed and was not fitted properly.
• Fitted:
• Below are shown brightest stars in one of the Location 1 images:
• Here is a zoomed in brightest star in the image just for reference:

Maximum Likelihood fitting

• The predicted pixel value for a pixel is the following:
• where is pixel coordinates, is the Gaussian, is the total number of pixel values.
• However, no integration was perfomed, the Gaussian was just calculated over the pixel.
• The maximum likelihood (Poissonian):
• where are the maximum number of pixels, is the data pixel value for individual pixel.
• The fitting done using it:

-- ElenaCukanovaite - 20 Jan 2016

Topic attachments
I Attachment History Action Size Date Who Comment
png median_15.png r1 manage 47.5 K 20 Jan 2016 - 23:22 ElenaCukanovaite
png median_30.png r1 manage 47.7 K 20 Jan 2016 - 23:22 ElenaCukanovaite
png mode_15.png r1 manage 47.9 K 20 Jan 2016 - 23:22 ElenaCukanovaite
png mode_30.png r1 manage 50.1 K 20 Jan 2016 - 23:22 ElenaCukanovaite
png all.png r1 manage 801.2 K 21 Jan 2016 - 18:58 ElenaCukanovaite
png 118_219.png r1 manage 106.6 K 21 Jan 2016 - 19:00 ElenaCukanovaite
png 276_306.png r1 manage 117.0 K 21 Jan 2016 - 19:00 ElenaCukanovaite
png 663_42.png r1 manage 104.8 K 21 Jan 2016 - 19:02 ElenaCukanovaite
png 664_369.png r1 manage 100.0 K 21 Jan 2016 - 19:02 ElenaCukanovaite
png 723_479.png r1 manage 100.2 K 21 Jan 2016 - 19:04 ElenaCukanovaite
png 746_164.png r1 manage 108.5 K 21 Jan 2016 - 19:04 ElenaCukanovaite
png 1178_776.png r1 manage 106.8 K 21 Jan 2016 - 19:05 ElenaCukanovaite
png 1226_746.png r1 manage 101.7 K 21 Jan 2016 - 19:05 ElenaCukanovaite
png 1273_587.png r1 manage 104.3 K 21 Jan 2016 - 19:05 ElenaCukanovaite
png zoomed_in_star.png r1 manage 85.5 K 21 Jan 2016 - 19:09 ElenaCukanovaite
png generated_field.png r1 manage 42.5 K 21 Jan 2016 - 23:26 ElenaCukanovaite
png log_gen_field.png r1 manage 62.7 K 21 Jan 2016 - 23:26 ElenaCukanovaite
png bg.png r1 manage 50.4 K 21 Jan 2016 - 23:28 ElenaCukanovaite
png removed_due_to_shape.png r1 manage 51.5 K 21 Jan 2016 - 23:30 ElenaCukanovaite
png histogram_width_ratios.png r1 manage 27.0 K 21 Jan 2016 - 23:32 ElenaCukanovaite
png distance.png r1 manage 32.2 K 21 Jan 2016 - 23:35 ElenaCukanovaite
png distance_star.png r1 manage 52.7 K 21 Jan 2016 - 23:35 ElenaCukanovaite
png distance_fixed.png r1 manage 32.2 K 21 Jan 2016 - 23:37 ElenaCukanovaite
png fixed_center.png r1 manage 89.0 K 22 Jan 2016 - 00:11 ElenaCukanovaite
png unfixed_best.png r1 manage 88.6 K 22 Jan 2016 - 00:19 ElenaCukanovaite

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Topic revision: r5 - 22 Jan 2016 - ElenaCukanovaite

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