Read color image into grayscale image using Java OpenCV library

Imgcodecs Class imread() method accepts a string representing the file name as the value of the parameter . This method reads the contents of the specified file into a matrix object and returns it. Using this method you can read the contents of the image.

Besides this, the Imgcodecs class also provides another variant of this method that accepts an integer value representing a flag specifying the desired reading mode.

p>

The following are the various fields of the Imgcodecs class that can be used as flag values.

• IMREAD_COLOR - If the flag is set to this value, the loaded image will be converted to a 3-channel BGR (Blue Green Red) color image.

• IMREAD_GRAYSCALE - If the flag is set to this value, the loaded image will be converted to a single channel grayscale image.

• IMREAD_LOAD_GDAL - If the flag is set to this value, images can be loaded using the GDAL driver.

• IMREAD_ANYCOLOR - If the flag is set to this value, the image will be read in any possible color format.

  li>

• ##IMREAD_REDUCED_COLOR_2 or,

  IMREAD_REDUCED_COLOR_4 or,
  IMREAD_REDUCED_COLOR_8

  - if the flag is set to this value When , the image is read as a three-channel BGR and the size of the image is reduced to 1/2, 1/4 or 1/8 of the original size of the image relative to the field used.

##IMREAD_REDUCED_GRAYSCALE_2 or, IMREAD_REDUCED_GRAYSCALE_4 or,

IMREAD_REDUCED_GRAYSCALE_8

- if the flag is set to this value , the image is read as a single-channel grayscale image, and the image size is reduced relative to the field used to 1/2, 1/4, or 1/8 of the original size of the image.

• IMREAD_UNCHANGED - If the flag is set to this value, the loaded image is returned as-is.

So if you need to read a color image into grayscale, you should pass IMREAD_GRAYSCALE or IMREAD_REDUCED_GRAYSCALE_X as parameter.

Example 1

import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;
public class ReadAsGreyScale {
   public static void main(String args[]) {
      //Loading the OpenCV core library
      System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
      //Reading the Image from the file
      Mat matrix = Imgcodecs.imread("D://images//sunset.jpg", Imgcodecs.IMREAD_GRAYSCALE);
      //Writing the image
      Imgcodecs.imwrite("D://images//sunset_greyscale.jpg", matrix);
      System.out.println("Image re-Saved");
   }
}

Enter

Output

##Example 2

import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;
public class ReadingAsGrey2 {
   public static void main(String args[]) {
      //Loading the OpenCV core library
      System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
      String input = "D://images//sunset.jpg";
      //Reading the Image from the file
      Mat matrix = Imgcodecs.imread(input, Imgcodecs.IMREAD_REDUCED_GRAYSCALE_4 );
      //Writing the image
      Imgcodecs.imwrite("D://images//sunset_grey_8.jpg", matrix);
      System.out.println("Image re-Saved");
   }
}

Output

The above is the detailed content of Read color image into grayscale image using Java OpenCV library. For more information, please follow other related articles on the PHP Chinese website!