Detecting hot pixels

  • We had two 1 hour exposure dark frames. One was at an angle and the other pointed upwards.
  • We wanted to find the x and y coordinates of hot pixels and the hotness of those pixels for each image.
  • Wrote a for loop program to do that.
  • Wanted to investigate if the hot pixels were clustered for each image.
  • To do that we plotted a histogram of the frequency of hot pixels in x and y coordinates for each image.
  • For the upwards picture 6951 pixels were found for the threshold of 2000.
  • For the image at an angle 5748 pixels were found for the threshold of 2000.
  • In total there are 1560600 pixels.

Histograms for x and y positions

  • x coordinate histograms for upwards and at an angle.
number_of_pixels_x_coordinate_upwards.png

number_of_pixels_x_coordinate_angle.png

  • y coordinate histograms for upwards and at an angle.
number_of_pixels_y_coordinate_upwards.png

number_of_pixels_y_coordinate_angle.png

  • The plots show where there are more hot pixels. In this case it is at the edges of the CCD.
  • Plots agree for both images.
  • For upwards image there are more hot pixels and it would explain why there are more pixels for a given x or y bin.

Histograms for hotness of pixels

  • The hotness of the hot pixels was plotted as a histrogram for both images.
hotness_histogram_upwards.png

hotness_histogram_angle.png

  • For both images the shape of the histogram is similar.
  • There is an unusual spike.
  • At an angle the spike is at 4000 pixel values, whereas when the camera is pointed upwards, the spike appears at 6000 pixel values.

Comparing hotness of the two independent 1 hour exposures

  • We wanted to investigate how the hotness changes with the angle of the camera.
  • We had two images, upwards and at an angle.
  • We matched the hot pixels between the two lists.
  • Some pixels were matched more than once, because some pixels had no corresponding hot pixel in the image, this is because the upward image had a lot more hot pixels.
  • The correspond histograms are shown below for different threshold pixel values.
30_bins_30000_thres.png

100_bins_3000_thres.png

  • Due to computing time many different threshold values were used.
  • We could only go down to 3000 pixel values as the threshold.
  • We expected a Gaussian centered on 0, because we expect a symmetric difference with the most common difference being zero, and the difference is less likely.
  • As can be seen, especially at large thresholds the shape deviates from a Gaussian and it is not centered on 0.
  • Some differences are very high.
  • For the threshold of 3000 pixel values, there were 5573 hot pixels for upwards image and 4453 hot pixels in the angle image.
  • It appears that there are always more hot pixels in the upwards image as compared to the image at an angle.
-- ElenaCukanovaite - 03 Nov 2015
Topic attachments
I Attachment Action Size Date Who Comment
PNGpng 100_bins_3000_thres.png manage 26.1 K 03 Nov 2015 - 15:56 ElenaCukanovaite  
PNGpng 30_bins_30000_thres.png manage 26.2 K 03 Nov 2015 - 15:56 ElenaCukanovaite  
Texttxt hot_pixels_angle.txt manage 118.3 K 03 Nov 2015 - 14:43 ElenaCukanovaite List of hot pixels. Column 1 is for x coordinates, column 2 is for y coordinates, column 3 is the hotness. This list was generated for the threshold of 2000 pixels.
Texttxt hot_pixels_upwards.txt manage 143.4 K 03 Nov 2015 - 14:43 ElenaCukanovaite List of hot pixels. Column 1 is for x coordinates, column 2 is for y coordinates, column 3 is the hotness. This list was generated for the threshold of 2000 pixels.
PNGpng hotness_histogram_angle.png manage 26.6 K 03 Nov 2015 - 13:47 ElenaCukanovaite  
PNGpng hotness_histogram_upwards.png manage 29.4 K 03 Nov 2015 - 13:47 ElenaCukanovaite  
PNGpng number_of_pixels_x_coordinate_angle.png manage 28.2 K 03 Nov 2015 - 13:28 ElenaCukanovaite  
PNGpng number_of_pixels_x_coordinate_upwards.png manage 29.1 K 03 Nov 2015 - 13:28 ElenaCukanovaite  
PNGpng number_of_pixels_y_coordinate_angle.png manage 30.3 K 03 Nov 2015 - 13:28 ElenaCukanovaite  
PNGpng number_of_pixels_y_coordinate_upwards.png manage 31.3 K 03 Nov 2015 - 13:28 ElenaCukanovaite  

Physics WebpagesRHUL WebpagesCampus Connect • Royal Holloway, University of London, Egham, Surrey TW20 0EX; Tel/Fax +44 (0)1784 434455/437520

Topic revision: r2 - 03 Nov 2015 - ElenaCukanovaite

 
This site is powered by the TWiki collaboration platformCopyright © 2008-2018 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding RHUL Physics Department TWiki? Send feedback