PK - Peak search

(10/10/14)

PURPOSE

Searches for local peaks in an image. This operation does NOT find "maximum" location when image has plateaus. It may even find the "last" value along the plateau. To overcome this use low pass filtration first or use 'PK M'.   Example.

SEE ALSO

PK M [Peak search - Maximum]
PK D [Peak search - output to Document file]
PK DR [Peak search - Restricted neighborhood, output to Document file]
PK 3 [Peak search - 3D]

USAGE

.OPERATION: PK [xi],[yi], [pk],[ratio], [xs],[ys], [pks]
[This operation can return up to seven optional register variables:
Variable Example Receives
First [xo] X integral pixel location of max relative to origin
Second [yo] Y integral pixel location of max relative to origin
Third [pk] Peak height (maximum)
Fourth [ratio] Ratio of peak height relative to the highest peak
Fifth [xs] X sub-pixel location of max relative to origin
Sixth [ys] Y sub-pixel location of max relative to origin
Seventh [pks] Peak height of the parabolically fitted peak

.INPUT FILE: IMG001
[Enter name of the input image.]

.NUMBER OF PEAKS, CENTER ORIGIN OVERRIDE (0/1): 12, 0
[Enter the number of peaks to be searched for. If an origin position other than at the image's center (NX/2 + 1, NY/2 + 1) is desired, enter '1' in the second position.]

If the option "CENTER ORIGIN OVERRIDE" is specified, SPIDER asks the next two questions:


.NEW ORIGIN COORDINATES: 1,1
[Enter the new origin coordinates.]

.PEAK NUMBER FOR RATIO: 1
[Enter the number of the peak relative to which the heights of the other peaks are calculated. This ratio is printed out and listed in the document file along with the other parameters of the peaks.]

NOTES

  1. In the above example, the computer will find the 12 largest peaks. These positions will be printed in the RESULTS file labeled as follows:
    NO IX IY XO YO HEIGHT RATIO
    NO Peak number
    IX Integer X peak location relative to image
    IY Integer Y peak location relative to image
    XO Integer X peak location relative to origin
    YO Integer Y peak location relative to origin
    HEIGHT Peak height
    RATIO Peak height relative to highest or specified peak
    The sub-pixel offset of a parabolically fitted peak and height of the peak will also be printed in the results file.

  2. Maxima occuring on the boundary of the image are IGNORED.

  3. The register variables from the command line (if any) can be used as input to a subsequent 'SH' (SHIFT) operation.

SUBROUTINES

SPEAK, PARABL

CALLER

UTIL1