MOPEX Online Manual
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APEX Modules: Gaussnoise
Output Directory Keyword: OUTPUT_DIR (apex_1frame.pl); COADD_DIR (apex.pl)
Default Output Directory: <output_dir> (apex_1frame.pl); <output_dir>/Coadd (apex.pl)
Depends on: Input Files
Important notes: if use_psp_to_detect is set in the namelist, and Input_Type = "snr_input" is set in the Detect module then Gaussnoise is run on the Point Source Probability images as well. In that case, the user must also include a parameter block called &PSP_GAUSSNOISE, with the parameter N_Outliers_Per_Window set to 0. See below for the full parameter block.
PURPOSE
-
This module estimates the background fluctuations in the input
image(s). It is very similar to Detect MedFilter. It finds the 68
percentile range of the pixel values in a sliding window in order to
measure the Gaussian noise.
PARAMETER BLOCK
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&GAUSSNOISE
Window_X = 45,
Window_Y = 45,
N_Outliers_Per_Window = 100,
Min_Good_Pixels_In_Window = 9,
Min_GoodNeighbours_Number = 4,
Max_BadPixels_OutputImage = 100,
&END
if use_psp_to_detect is set in the namelist (see APEX Namelist Options, under C: Other Options, for more information), and Input_Type = "snr_input" is set in the Detect module then you must also include the following parameter block. N_Outliers_Per_Window must be set to 0:
&PSP_GAUSSNOISE
Window_X = 45,
Window_Y = 45,
N_Outliers_Per_Window = 0,
&END
INPUTS
Window_X: (int) the X size in pixels of the window used to compute the median of the background. The default value is 45
Window_Y: (int) the Y size in pixels of the window used to compute the median of the background. The default value is 45
N_Outliers_Per_Window: (int) the number of outlier pixels (N) being rejected from the X*Y window when computing the noise.
Min_Good_Pixels_In_Window: (int) The minimum number of good (non-NaN, non-masked) pixels needed to compute the noise. If insufficient good pixels are present, the "missing" output pixel is replaced by the interpotion of its neighbors.
Min_GoodNeighbors_Number: (int) The minimum number of good neighbor pixels need to perform the replacement of "missing" output pixels.
Max_BadPixels_OutputImage: (int) The maximum number of allowed bad (NaN) pixels in the output image.
OUTPUTS
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Generated FITS (*_noise.fits): The output is the tile noise
image(s) measured from the input image(s).
DISCUSSION
The program computes the Gaussian noise (68 percentile) for each pixel in the input image using a rectangular window of Window_X by Window_Y pixels. It is achieve by omitting the N_Outliers_Per_Window highest pixels from each median window. There is a minimum required number of good (not-NAN and not marked by any mask) pixels per median window Min_Good_Pixels_In_Window. If the number of good pixels is below this threshold then the corresponding pixel in the output image is marked as a "missing" pixel. When the median calculation is finished, the values of the marked pixels are interpolated from the neighboring pixels for which the median has been found. In order to do so the program scans around the pixel in question and accumulates values of good pixels. When the number of accumulated values reaches or exceeds the minimum number given by the input parameter Min_GoodNeighbors_Number the program finds the average and stores this value as the median for the pixel in question.| Contents | ~ | Previous: APEX Modules - Detect MedFilter | ~ | Next: APEX Modules - Point Source Probability |
