[python] Computing cross-correlation function?

If you are looking for a rapid, normalized cross correlation in either one or two dimensions I would recommend the openCV library (see http://opencv.willowgarage.com/wiki/ http://opencv.org/). The cross-correlation code maintained by this group is the fastest you will find, and it will be normalized (results between -1 and 1).

While this is a C++ library the code is maintained with CMake and has python bindings so that access to the cross correlation functions is convenient. OpenCV also plays nicely with numpy. If I wanted to compute a 2-D cross-correlation starting from numpy arrays I could do it as follows.

import numpy
import cv

#Create a random template and place it in a larger image
templateNp = numpy.random.random( (100,100) )
image = numpy.random.random( (400,400) )
image[:100, :100] = templateNp

#create a numpy array for storing result
resultNp = numpy.zeros( (301, 301) )

#convert from numpy format to openCV format
templateCv = cv.fromarray(numpy.float32(template))
imageCv = cv.fromarray(numpy.float32(image))
resultCv =  cv.fromarray(numpy.float32(resultNp))

#perform cross correlation
cv.MatchTemplate(templateCv, imageCv, resultCv, cv.CV_TM_CCORR_NORMED)

#convert result back to numpy array
resultNp = np.asarray(resultCv)

For just a 1-D cross-correlation create a 2-D array with shape equal to (N, 1 ). Though there is some extra code involved to convert to an openCV format the speed-up over scipy is quite impressive.

Examples related to python

programming a servo thru a barometer Is there a way to view two blocks of code from the same file simultaneously in Sublime Text? python variable NameError Why my regexp for hyphenated words doesn't work? Comparing a variable with a string python not working when redirecting from bash script is it possible to add colors to python output? Get Public URL for File - Google Cloud Storage - App Engine (Python) Real time face detection OpenCV, Python xlrd.biffh.XLRDError: Excel xlsx file; not supported Could not load dynamic library 'cudart64_101.dll' on tensorflow CPU-only installation

Examples related to r

How to get AIC from Conway–Maxwell-Poisson regression via COM-poisson package in R? R : how to simply repeat a command? session not created: This version of ChromeDriver only supports Chrome version 74 error with ChromeDriver Chrome using Selenium How to show code but hide output in RMarkdown? remove kernel on jupyter notebook Function to calculate R2 (R-squared) in R Center Plot title in ggplot2 R ggplot2: stat_count() must not be used with a y aesthetic error in Bar graph R multiple conditions in if statement What does "The following object is masked from 'package:xxx'" mean?

Examples related to statistics

Function to calculate R2 (R-squared) in R pandas: find percentile stats of a given column What exactly does numpy.exp() do? Find p-value (significance) in scikit-learn LinearRegression How to plot ROC curve in Python Pandas - Compute z-score for all columns Calculating percentile of dataset column How to normalize an array in NumPy to a unit vector? How to find row number of a value in R code np.mean() vs np.average() in Python NumPy?

Examples related to numpy

Unable to allocate array with shape and data type How to fix 'Object arrays cannot be loaded when allow_pickle=False' for imdb.load_data() function? Numpy, multiply array with scalar TypeError: only integer scalar arrays can be converted to a scalar index with 1D numpy indices array Could not install packages due to a "Environment error :[error 13]: permission denied : 'usr/local/bin/f2py'" Pytorch tensor to numpy array Numpy Resize/Rescale Image what does numpy ndarray shape do? How to round a numpy array? numpy array TypeError: only integer scalar arrays can be converted to a scalar index

Examples related to scipy

Reading images in python Numpy Resize/Rescale Image How to get the indices list of all NaN value in numpy array? ImportError: cannot import name NUMPY_MKL numpy.where() detailed, step-by-step explanation / examples Scikit-learn train_test_split with indices Matplotlib: Specify format of floats for tick labels Installing NumPy and SciPy on 64-bit Windows (with Pip) Can't install Scipy through pip Plotting a fast Fourier transform in Python