CODEWITHSUNDEEP
opencv
user522659
user522659

Reputation: 41

Horizontal Histogram in OpenCV

I am newbie to OpenCV,now I am making a senior project related Image processing. I have a question: Can I make a horizontal or vertical histogram with some functions of OpenCV? Thanks,

Truong

Upvotes: 4

Views: 12125

Answers (4)

snoob dogg
snoob dogg

Reputation: 2875

An example of using cv2.reduce with OpenCV 3 in Python : 

import numpy as np
import cv2

img = cv2.imread("test_1.png") 

x_sum = cv2.reduce(img, 0, cv2.REDUCE_SUM, dtype=cv2.CV_32S) 
y_sum = cv2.reduce(img, 1, cv2.REDUCE_SUM, dtype=cv2.CV_32S)

Upvotes: 0

omotto
omotto

Reputation: 1879

Updating carnieri answer (some cv functions are not working today)

import numpy as np
import cv2

def verticalProjection(img):
    "Return a list containing the sum of the pixels in each column"
    (h, w) = img.shape[:2]
    sumCols = []
    for j in range(w):
        col = img[0:h, j:j+1] # y1:y2, x1:x2
        sumCols.append(np.sum(col))
    return sumCols

Regards.

Upvotes: 1

rold2007
rold2007

Reputation: 1327

The most efficient way to do this is by using the cvReduce function. There's a parameter to allow to select if you want an horizontal or vertical projection.

You can also do it by hand with the functions cvGetCol and cvGetRow combined with cvSum.

Upvotes: 7

carnieri
carnieri

Reputation: 1353

Based on the link you provided in a comment, this is what I believe you're trying to do.

You want to create an array with n elements, where n is the number of columns in the input image. The value of the nth element of the array is the sum of all the pixels in the nth column.

You can calculate this array by looping over the columns of the input image, using cvGetSubRect to access the pixels in that column, and cvSum to sum those pixels.

Here is some Python code that does that, assuming a grayscale image:

import cv

def verticalProjection(img):
    "Return a list containing the sum of the pixels in each column"
    (w,h) = cv.GetSize(img)
    sumCols = []
    for j in range(w):
        col = cv.GetSubRect(img, (j,0,1,h))
        sumCols.append(cv.Sum(col)[0])
    return sumCols

Upvotes: 1

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