Python image Processing (5): Histogram

Happy Shrimp

http://blog.csdn.net/lights_joy/

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the histogram is calculated using OpenCV of the calchist completed.

OpenCV of the C + + in the interface calchist There are three kinds of forms:

//! Computes the joint dense histogram for a set of images.                          cv_exports void Calchist (const mat* images, int nimages, const int* channels, Inputarray mask, Outputarray hist, int dims, const int* histsize, const float** ranges, Bo OL uniform=true, BOOL accumulate=false);//! Computes the joint sparse histogram for a set of images.                          cv_exports void Calchist (const mat* images, int nimages, const int* channels, Inputarray mask,                           sparsemat& hist, int dims, const int* histsize, const float** ranges, BOOL Uniform=true, bool accumulate=false);                            Cv_exports_w void Calchist (inputarrayofarrays images, const vector<int>& channels, Inputarray Mask, Outputarray hist, const vector<int>& hists ize, Const Vector<float>& ranges, bool accumulate=false); 

but the exported Python The interface has only one:

Static pyobject* pyopencv_calchist (pyobject*, pyobject* args, pyobject* kw) {pyobject* pyobj_images = NULL;    Vector_mat images;    pyobject* pyobj_channels = NULL;    Vector_int channels;    pyobject* pyobj_mask = NULL;    Mat Mask;    pyobject* pyobj_hist = NULL;    Mat hist;    pyobject* pyobj_histsize = NULL;    Vector_int histsize;    pyobject* pyobj_ranges = NULL;    Vector_float ranges;    BOOL Accumulate=false;    Const char* keywords[] = {"Images", "channels", "Mask", "histsize", "Ranges", "hist", "Accumulate", NULL}; if (pyarg_parsetupleandkeywords (args, kw, "ooooo| Ob:calchist ", (char**) keywords, &pyobj_images, &pyobj_channels, &pyobj_mask, &pyobj_histsize, & Pyobj_ranges, &pyobj_hist, &accumulate) && pyopencv_to (pyobj_images, Images, Arginfo ("Images", 0)) && pyopencv_to (pyobj_channels, channels, Arginfo ("channels", 0)) && pyopencv_to (Pyobj_mask, Mask, Arginfo ("mask", 0)) && pyopeNcv_to (Pyobj_hist, Hist, Arginfo ("hist", 1)) && pyopencv_to (pyobj_histsize, Histsize, Arginfo ("Histsize", 0 )) && pyopencv_to (pyobj_ranges, Ranges, Arginfo ("ranges", 0)) {ERRWRAP2 (cv::calchist,        Channels, Mask, Hist, histsize, ranges, accumulate);    Return Pyopencv_from (hist); } return NULL;

so Python the interface looks a bit strange:

hist = Cv2.calchist ([src], [0], None, [256], [0, 255])

Even if you operate on only one picture, you must use the form of an array for parameter passing.

Write a simple Python program to get a histogram of a single channel:

#-*-coding:utf-8-*-import cv2import numpy as Npimport Matplotlib.pyplot as plt# single-channel histogram test src = cv2.imread (' F:\\tmp\\co Tton.jpg ') cv2.imshow (' src ', src) hist = cv2.calchist ([src], [0], None, [], [0, 255]) Plt.plot (hist) plt.show () Cv2.waitkey ()

The results are as follows:

Meet our expectations of the histogram.

??

Python image Processing (5): Histogram