OpenCV Tutorials

ITo load an image or convert an OpenCV image in grayscale, simply use the code below:

OpenCV C++ image grayscale:

#include <opencv2>
#include <opencv2>
#include <stdio.h>

using namespace cv;

int main( int argc, char** argv )
{
 char* imageName = argv[1];

 Mat image;
 image = imread( imageName, 0 );

 if( argc != 2 || !image.data )
 {
   printf( " No image data \n " );
   return -1;
 }

 namedWindow( imageName, CV_WINDOW_AUTOSIZE );
 imshow( imageName, image );
 waitKey(0);

 return 0;
}</stdio.h></opencv2></opencv2>

#include

using namespace cv;

int main( int argc, char** argv )

{

char* imageName = argv[1];

Mat image;

image = imread( imageName, 0 );

if( argc != 2 || !image.data )

{

printf( " No image data \n " );

return -1;

}

namedWindow( imageName, CV_WINDOW_AUTOSIZE );

imshow( imageName, image );

waitKey(0);

return 0;

}

OpenCV Python image grayscale:

import cv2
import numpy as np
from matplotlib import pyplot as plt

img = cv2.imread('cat.jpg',0)

cv2.imshow('Image', img)
cv2.waitKey(0)
cv2.destroyAllWindows()

import cv2

import numpy as np

from matplotlib import pyplot as plt

img = cv2.imread('cat.jpg',0)

cv2.imshow('Image', img)

cv2.waitKey(0)

cv2.destroyAllWindows()

Altternatively, you can convert a color image to grayscale.

import cv2
import numpy as np
from matplotlib import pyplot as plt

img = cv2.imread('cat.jpg')
gray_image = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

cv2.imshow('Image', gray_image)
cv2.waitKey(0)
cv2.destroyAllWindows()

import cv2

import numpy as np

from matplotlib import pyplot as plt

img = cv2.imread('cat.jpg')

gray_image = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

cv2.imshow('Image', gray_image)

cv2.waitKey(0)

cv2.destroyAllWindows()

Output:

OpenCV Grayscale image cat

OpenCV Images are held in the Mat data structure. The IplImage data structure is deprecated. OpenCV offers support for the image formats Windows bitmap (bmp), portable image formats (pbm, pgm, ppm) and Sun raster (sr, ras). With help of plugins you may also load image formats like JPEG (jpeg, jpg, jpe), JPEG 2000 (jp2), TIFF files (tiff, tif) and portable network graphics (png).

OpenCV Load Image C++
To load and display an image using OpenCV:

// OpenCV Load and display image, https://talkera.org/opencv
#include <opencv2>
#include <opencv2>
#include <stdio.h>

using namespace cv;

int main( int argc, char** argv )
{
 char* imageName = argv[1];

 Mat image;
 image = imread( imageName, 1 );

 if( argc != 2 || !image.data )
 {
   printf( " No image data \n " );
   return -1;
 }
 namedWindow( imageName, CV_WINDOW_AUTOSIZE );
 imshow( imageName, image );
 waitKey(0);

 return 0;
}</stdio.h></opencv2></opencv2>

// OpenCV Load and display image, https://talkera.org/opencv

#include

using namespace cv;

int main( int argc, char** argv )

{

char* imageName = argv[1];

Mat image;

image = imread( imageName, 1 );

if( argc != 2 || !image.data )

{

printf( " No image data \n " );

return -1;

}

namedWindow( imageName, CV_WINDOW_AUTOSIZE );

imshow( imageName, image );

waitKey(0);

return 0;

}

Compilation:

g++ -w image.cpp -o image  -fpermissive `pkg-config --libs opencv`
./image cat.jpg

1 2	g++ -w image.cpp -o image -fpermissive `pkg-config --libs opencv` ./image cat.jpg

Output:

OpenCV Window

OpenCV Load Image Python

import cv2
import numpy as np
from matplotlib import pyplot as plt

img = cv2.imread('cat.jpg')

cv2.imshow('OpenCV Load Image ', img)
cv2.waitKey(0)
cv2.destroyAllWindows()

import cv2

import numpy as np

from matplotlib import pyplot as plt

img = cv2.imread('cat.jpg')

cv2.imshow('OpenCV Load Image ', img)

cv2.waitKey(0)

cv2.destroyAllWindows()

Convert OpenCV image to grayscale

Loading an image in OpenCV