Peakfinder
A set of peak-finding algorithms developed for analysis of data from LCLS pixel array detectors.
Interface
from ... import imagealgos peaks = imagealgos.peaks_adapt_thr(data, mask, nsigm, rank, base_r, base_dr, do_base_sub=False, npix_min=None, npix_max=None, thr_atot=None, son_min=None) peaks = imagealgos.peaks_two_thr(data, mask, thr_low, thr_high, rank, base_r, base_dr, do_base_sub=False, npix_min=None, npix_max=None, thr_atot=None, son_min=None)
Input
arguments:
data :
1) numpy.array, ndim=2
- 2-d data array for processing
2) [numpy.array
] - list of 2-d data arrays for processing, ndim=2
3) numpy.array
,
- a set of 2-d data arrays for processing; last two indexes are used as 2-d row and column, higher indexes compacted to the segment indexndim>2
keyword arguments for peak finding:
mask : numpy.array (shape,dtype=np.uint16) | None
- expected the same shape/structure as data
- pixel mask with 0/1 for bad/good pixel
rank : int
- radial size of the region (2*rank+1
rows and columns) around pixel for peak finding
thr
_low : float
- low threshold on pixel intensity for 'peaks_two_thr'
finder
thr_high
: float
- high threshold on pixel intensity for 'peaks_two_thr'
finder
base_r
: float
- internal radius of the ring for evaluation of base level mean and rms (noise)
base_dr
: float
- width of the ring for evaluation of base level mean and rms (noise)
nsigm : float
- threshold in number of noise rms for peaks_adapt_thr
keyword arguments for peak selection:
npix_min
: int
- minimum number of pixels in the peak
npix_max
: int
- maximum number of pixels in the peak
thr_atot
: float
- threshold on total peak intensity
son_min
: float
- threshold on signal over noise (S/N) value
Output
peaks
:
dict of
arrays/lists - most natural to work with a single values for many peaks
peaks keywords:
seg : int
- 2-d segment index beginning from 0, e.g. in CSPAD this index should be in the range from 0 to 31row : int
- row (beginning from 0) of the pixel with maximal intensitycol : int
- column (beginning from 0) of the pixel with maximal intensitynpix : int
- number of pixels accounted in the peakamp_max : float
- maximal intensity among peak pixelsamp_total : float
- total intensity of pixels accounted in the peakrow_cgmean : float
- row coordinate mean value evaluated in the "center of gravity" algorithm for pixels accounted in the peak using their intensities as weightscol_cgmean : float
- column coordinate mean value evaluated in the "center of gravity" algorithmraw_cgrms : float
- row coordinate rms spread value evaluated in the "center of gravity" algorithmcol_cgrms : float
- column coordinate rms spread value evaluated in the "center of gravity" algorithmbase : float
- per pixel base level mean estimated for pixels in the ring region (parameters
) around peak centerbase_r
, base_dr
noise : float
- per pixel base level rms estimated for pixels in the ring region (parameters
) around peak centerbase_r
, base_dr
son : float
- signal over noise ratio estimated asamp_total
/(noise * sqrt(
npix
))peak : list - of peak objects
peak attributes:pixinds : list
- list of peak indextuple
(row, col
) for pixels accounted in the peak
row_min() : int
- minimal row of the pixel group accounted in the peakrow_max() : int
- maximal row of the pixel group accounted in the peakcol_min() : int
- minimal column of the pixel group accounted in the peakcol_max() : int
- maximal column of the pixel group accounted in the peak- other methods of data processing for
pixinds
Peak-finding algorithms
Method peakfinder is a wrapper around a few algorithms. First argument mode
switches between different peak-finding algorithms. Each algorithm works in a few stages. First stage is a search for peak candidates or "seed" peaks and this is a most distinctive part between algorithms:
- peaks_two_thr - or peak-finder is a two-threshold algorithm searching for groups of connected pixels with intensity above
thr
_low
around group central pixel with intensity exceedingthr_high
in the region restricted by the radial parameterrank
. In the loop over all pixels each pixel with intensity grater or equalthr_high
is considered as a peak candidate. For each candidate recursive algorithm is launched and searches for a group of connected pixels with intensity grater or equalthr
_low
in the square region with dimensions2*rank+1
pixel in rows and columns. Pixels of the group are marked as busy on 2-d map and are not used for other groups. Central pixel of the peak candidate should have maximal intensity in the group of connected pixels, otherwise recursion is terminated and all group pixels released for further search. Two neighbor pixels with intensity abovethr
_low
having common boarder are assumed connected. Two pixels having a single common vertex are assumed disconnected. Base level mean,bkgd
, and, rms,noise
values are evaluated for pixels in the ring with internal radiusbase_r
and widthbase_dr
around central pixel. Pixels with intensity abovethr
_low
are excluded from evaluation of the base level parameters. - peaks_adapt_thr - searches peak candidates as group of connected pixels with intensity above dynamically estimated threshold around local intensity maximums of specified
rank
. Maps of local maximums and minimums of specifiedrank
are generated fordata
array. Parameterrank
defines a square region with dimensions2*rank+1
pixels in rows and columns around center pixel. Each local maximum is considered as a peak candidate. Its base level mean,bkgd
, and rms ,noise
, values are evaluated using surrounding pixels in the ring with internal radiusbase_r
and widthbase_dr
. Pixels marked as local maximums and minimums (for symmetry) of specified rank in rows and columns are excluded in evaluation of the base level parameters.NOTE:
due to excluded extremes the base level rms is under-estimated in this algorithm, so, set parameternsigm
wisely. Then, for each peak candidate local threshold parameterthr=
(no exclusion forbkgd
+nsigm*noisensigm=0
) is used. Recursive algorithm searches for the group of connected pixels with intensity above local thresholdthr
in therank
-restricted region.
Other stages of all algorithms are about the same.
- returned values of
amp_max
andamp_total
are base level corrected by subtractingbkgd
andbkgd
*
, respectivelynpix
- signal over noise
son
is evaluated asamp_total
/(noise * sqrt(
,npix
)) - output list of peaks is generated from the list of seed peaks complying with selection parameters
npix_min, npix_max, amax_thr, atot_thr, son_min
.
Comments
- Chuck: use specific methods in stead of single wrapper
- Chris:
- look at scipy optimize, skimage ransac
- think about returning dictionary vs. object with attributes
- consider make row_min a method
- turn off background subtraction in intuitive way? base_r=None or base_dr=None
- vote to do v4 only for now
- all kwarg
- worry about seg
- vote to only support 2D array, at least at beginning
- add option to skip background correction
- 2016-11-09 grp mtg (Chris, David, Wilko):
- use meaningful parameters
- separate arguments and keywards with default parameters
- check input validity (i.e. pyvalid) that keyargs are not misspelled.
- peaks - dict(arrays)