findpeaks image lines contrast
image
Image to be searched.
lines
Sample image lines in which the peaks are to be found.
contrast
Maximum contrast between the highest peak and the lowest peak.
separation = 5
Minimum separation in pixels between acceptable peaks.
edge = 0
Minimum distance in pixels to the edge of the image for acceptable peaks.
threshold = 0.
The minimum acceptable peak pixel value.
min_npeaks = 1
Minimum number of peaks to be found. It is an error for fewer than
this number of peaks to be found.
max_npeaks = 1000
Maximum number of peaks to be found. If more than this number of peaks
is found then only the those with the highest peak values are accepted.
columns = '*'
Columns to be searched.
naverage = 20
Number of image lines around the sample line to be averaged before
finding the peaks.
debug = no
Print detailed information on the progress of the peak finding algorithm.
For each specified sample image line the number of peaks and their column positions in the image are determined. The number of peaks and their positions are assumed to correspond to points along the spectra. This information is entered in the MULTISPEC database.
The naverage image lines about the specified sample line are first averaged. The local maxima in the average line are then located in the specified columns more than the minimum distance from the edge of the image. A minimum peak pixel value cutoff is determined as the maximum of the specified threshold and contrast times the largest peak pixel value. All local maxima with pixel values below the cutoff are rejected. Next all peaks with separations less than separation from a stronger peak are rejected. Finally, if there are more than max_npeaks remaining only the max_npeaks strongest peaks are accepted. If fewer than min_npeaks are found then the task quits with an error.
If the number of spectra has been previously determined, such as by an earlier use of findpeaks, then it is an error if a different number of peaks is found.
The parameters of this task provide a great deal of flexibility in automatically determining the number and positions of the peaks. The most automatic method just uses the contrast to limit the acceptable peaks:
cl> findpeaks image.db 1 .1
However, if the number of spectra in the image is known:
cl> findpeaks image.db 1 0 min=10 max=10
or if a threshold is known:
cl> findpeaks image.db 1 0 threshold = 1000
For a noisy image the separation parameter can be set to eliminate spurious noise peaks near the peaks to be found:
cl> findpeaks image.db 1 .1 sep=20