Unable to down scale gray scale image

Question

I have an grayscale image with dimension 256*256.I am trying to downscale it to 128*128. I am taking an average of two pixel and writing it to the ouput file.

class Start {

 public static void main (String [] args) throws IOException {

 File input= new File("E:\\input.raw");

 File output= new  File("E:\\output.raw");
 new Start().resizeImage(input,output,2);

 }



 public  void resizeImage(File input, File output, int downScaleFactor) throws IOException {
          byte[] fileContent= Files.readAllBytes(input.toPath());
          FileOutputStream  stream= new FileOutputStream(output);
          int i=0;
          int j=1;
          int result=0;
          for(;i<fileContent.length;i++)
          {
                if(j>1){
                    // skip the records.
                    j--;
                    continue;
                }
                else { 
                    result = fileContent[i];
                    for (; j < downScaleFactor; j++) {
                        result =  ((result + fileContent[i + j]) / 2);
                    }
                    j++;
                    stream.write( fileContent[i]);
                }
          }
        stream.close();
      }

}

Above code run successfully , I can see the size of output file size is decreased but when I try to convert output file (raw file) to jpg online (https://www.iloveimg.com/convert-to-jpg/raw-to-jpg) it is giving me an error saying that file is corrupt. I have converted input file from same online tool it is working perfectly. Something is wrong with my code which is creating corrupt file. How can I correct it ?

P.S I can not use any library which directly downscale an image .

Answer 1

Your code is not handling image resizing.

See how-to-resize-images-in-java.

Which, i am copying a simple version here:

import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class ImageResizer {

    public static void resize(String inputImagePath,
            String outputImagePath, int scaledWidth, int scaledHeight)
            throws IOException {
        // reads input image
        File inputFile = new File(inputImagePath);
        BufferedImage inputImage = ImageIO.read(inputFile);

        // creates output image
        BufferedImage outputImage = new BufferedImage(scaledWidth,
                scaledHeight, inputImage.getType());

        // scales the input image to the output image
        Graphics2D g2d = outputImage.createGraphics();
        g2d.drawImage(inputImage, 0, 0, scaledWidth, scaledHeight, null);
        g2d.dispose();

        // extracts extension of output file
        String formatName = outputImagePath.substring(outputImagePath
                .lastIndexOf(".") + 1);

        // writes to output file
        ImageIO.write(outputImage, formatName, new File(outputImagePath));
    }

    public static void resize(String inputImagePath,
            String outputImagePath, double percent) throws IOException {
        File inputFile = new File(inputImagePath);
        BufferedImage inputImage = ImageIO.read(inputFile);
        int scaledWidth = (int) (inputImage.getWidth() * percent);
        int scaledHeight = (int) (inputImage.getHeight() * percent);
        resize(inputImagePath, outputImagePath, scaledWidth, scaledHeight);
    }

    public static void main(String[] args) {
        String inputImagePath = "resources/snoopy.jpg";
        String outputImagePath1 = "target/Puppy_Fixed.jpg";
        String outputImagePath2 = "target/Puppy_Smaller.jpg";
        String outputImagePath3 = "target/Puppy_Bigger.jpg";

        try {
            // resize to a fixed width (not proportional)
            int scaledWidth = 1024;
            int scaledHeight = 768;
            ImageResizer.resize(inputImagePath, outputImagePath1, scaledWidth, scaledHeight);

            // resize smaller by 50%
            double percent = 0.5;
            ImageResizer.resize(inputImagePath, outputImagePath2, percent);

            // resize bigger by 50%
            percent = 1.5;
            ImageResizer.resize(inputImagePath, outputImagePath3, percent);

        } catch (IOException ex) {
            System.out.println("Error resizing the image.");
            ex.printStackTrace();
        }
    }

}