Creating a simple black image with opencv using cvcreateimage - image

Question

Very basic question coming from a newbie in OpenCV. I just want to create an image with every pixel set to 0 (black). I have used the following code in the main() function:
IplImage* imgScribble = cvCreateImage(cvSize(320, 240), 8, 3);
And what I get is a solid gray image, instead of the black one.
Thanks in advance !

Answer 1

What version of opencv you are using?
For Mat,
#include <opencv2/opencv.hpp>
cv::Mat image(320, 240, CV_8UC3, cv::Scalar(0, 0, 0));

Answer 2

I can suggest two more altrnatives:
IplImage* imgScribble = cvCreateImage(cvSize(320, 240), 8, 3);
// Here you can set any color
cvSet(imgScribble, cvScalar(0,0,0));
// Here only black
cvZero(imgScribble);

Answer 3

The call to
cvCreateImage(cvSize(320, 240), 8, 3);
Create the image in the memory, but I don't think it initialize the data.
You should try this to initialize :
step= imgScribble->widthStep;
data = (uchar *)imgScribble->imageData;
for(i=0;i<imgScribble->height;i++) for(j=0;j<img->width;j++) for(k=0;k<3;k++)
data[i*step+j*3+k]=0;
(Inspired from this (Example C Program))

Answer 4

For Python:
import numpy as np
X_DIMENSION = 288
Y_DIMENSION = 382
black_image = np.zeros((X_DIMENSION, Y_DIMENSION))
With this code you generate a numpy array which is what is expected for opencv images and fill it with zero which is the color for black. This code is made for grayscale images. If you want it to be an RGB black image, just add 3 at the end of the tupple to create the dimensions np.zeros((X_DIMENSION, Y_DIMENSION, 3))

Answer 5

black and white image mean single channel image. you can simply created it as follows.
Mat img(500, 1000, CV_8UC1, Scalar(a));
"a" in between 0-255
you can see more examlpe and details from following page
https://progtpoint.blogspot.com/2017/01/tutorial-3-create-image.html

Answer 6

Here is my contribution:
cv::Mat output = cv::Mat::zeros(cv::Size(320, 240), CV_8UC3);

Answer 7

#include "stdafx.h"
#include <opencv/cxcore.h>
#include <opencv/highgui.h>
#include <iostream>
using namespace cv;
using namespace std;
#define LOAD_OPTION CV_LOAD_IMAGE_COLOR
int main( int argc, char** argv )
{
IplImage *image;
image = cvLoadImage("picture.jpg",0); // 0 : BLACK AND WHITE , Without 0 -> Color Picture
cvNamedWindow("Image",CV_WINDOW_AUTOSIZE);
cvShowImage("Image", image);
waitKey(-1);
return 0;
}