[FIXED] Why is the color of my image changed after writing it as a jpg file?

Issue

I'm currently making a method that converts a ppm file to a jpg, png, and bmp file. The way I did it is reading the content of a ppm file, creating a BufferedImage, and assigning each pixel from the ppm file to the corresponding pixel in the BufferedImage. My bmp and png files look correct. However, the jpg file looks completely different.

Below is my code:

import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferInt;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

import javax.imageio.ImageIO;

public class readPPMOutputOthers {

  public static void main(String[] args) throws InterruptedException {
    // read a ppm file

    Scanner sc;
    // if the file is not found, it will throw an exception
    try {
      sc = new Scanner(new FileInputStream("res/test2.ppm"));
    } catch (FileNotFoundException e) {
      throw new IllegalArgumentException("File not found!");
    }

    // the file now is a StringBuilder
    // read line by line to get information
    StringBuilder builder = new StringBuilder();
    while (sc.hasNextLine()) {
      String s = sc.nextLine();
      // ignore comment #
      if (s.charAt(0) != '#') {
        builder.append(s).append(System.lineSeparator());
      }
    }

   
    sc = new Scanner(builder.toString());
    String token;
    token = sc.next();

    // set the fields
    // initial load image
    int width = sc.nextInt();
    int height = sc.nextInt();
    int maxValue = sc.nextInt();

    List<Integer> pixels = new ArrayList<>();
    for (int i = 0; i < height; i++) {
      for (int j = 0; j < width; j++) {
        int r = sc.nextInt();
        int g = sc.nextInt();
        int b = sc.nextInt();

        int rgb = r;
        rgb = (rgb << 8) + g;
        rgb = (rgb << 8) + b;
        pixels.add(rgb);
      }
    }

    // make a BufferedImage from pixels
    BufferedImage outputImg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    int[] outputImagePixelData = ((DataBufferInt) outputImg.getRaster().getDataBuffer()).getData();

    for (int i = 0; i < pixels.size(); i++) {
      outputImagePixelData[i] = pixels.get(i);
    }

    try {
        ImageIO.write(outputImg, "png",
            new File("res/test.png"));
      ImageIO.write(outputImg, "jpg",
          new File("res/test2.jpg"));
        ImageIO.write(outputImg, "bmp",
            new File("res/test.bmp"));
    } catch (IOException e) {
      System.out.println("Exception occurred :" + e.getMessage());
    }
    System.out.println("Images were written successfully.");
  }
}

images comparison

The weird thing is it works for a very large image but not for this small image. I need to make it work for such small images because of testing. I've been digging posts about this on google and still didn't find a way to solve this. Any help would be appreciated!

Solution

The reason for the strange colors is YUV420 chroma subsumpling used by JPEG encoding.

In YUV420 every 2x2 pixels have the same chroma information (the 2x2 pixels have the same color).
The 2x2 pixels have the same color, but each pixel has different luminance (brighness).

---

The YUV420 Chroma subsumpling is demonstrated in Wikipedia:

And in our case:
becomes
The brown color is a mixture of the original red, cyan magenta and the yellow colors (the brown color is "shared" by the 4 pixels).

---

• Note:
  Chroma subsumpling is not considered as "compression", is the sense that it not performed as part of the JPEG compression stage.
  We can't control the chroma subsumpling by setting the compression quality parameter.
  Chroma subsumpling is referred as part of the "color format conversion" pre-processing stage - converting from RGB to YUV420 color format.

---

The commonly used JPEG color format is YUV420, but JPEG standard does support YUV444 Chroma subsumpling.
GIMP manages to save JPEG images with YUV444 Chroma subsumpling.

Example (2x2 image):
Too small: Enlarged:

I couldn't find an example for saving YUV444 JPEG in JAVA...

Answered By - Rotem

Answer Checked By - Cary Denson (PHPFixing Admin)

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[FIXED] Why is my gif image sent from servlet not animating?

Issue

I have this following code in my servlet

 response.setContentType("image/gif");
 String filepath = "PATH//TO//GIF.gif";
 OutputStream out = response.getOutputStream();
 File f = new File(filepath);
 BufferedImage bi = ImageIO.read(f);
 ImageIO.write(bi, "gif", out);
 out.close();

This code is just returning first frame of the image.

How to achieve returning full GIF image ?

Solution

Your GIF does not animate, because you are sending only the first frame to the client. :-)

Actually, you are, because ImageIO.read reads only the first frame (and a BufferedImage can only contain a single frame/image). You are then writing that single frame to the servlet output stream, and the result will not animate (it should be possible to create animating GIFs using ImageIO, but the code to do so will be quite verbose, see How to encode an animated GIF in Java, using ImageWriter and ImageIO? and Creating animated GIF with ImageIO?).

The good news is, the solution is both simple, and will save you CPU cycles. There's no need to involve ImageIO here, if you just want to send an animated GIF that you have stored on disk. The same technique can be used to send any binary content, really.

Instead, simply do:

response.setContentType("image/gif");
String filepath = "PATH//TO//GIF.gif";
OutputStream out = response.getOutputStream();

InputStream in = new FileInputStream(new File(filepath));
try {
    FileUtils.copy(in, out);
finally {
    in.close();
}

out.close();

FileUtils.copy can be implemented as:

public void copy(final InputStream in, final OutputStream out) {
    byte[] buffer = new byte[1024]; 
    int count;

    while ((count = in.read(buffer)) != -1) {
        out.write(buffer, 0, count);
    }

    // Flush out stream, to write any remaining buffered data
    out.flush();
}

Answered By - Harald K

Answer Checked By - Terry (PHPFixing Volunteer)

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