Why is the size of new image constructed using Bufferd Image class less?

Question

I am trying to compress image losslessly, for start I what I am doing is:
step1. Access pixels of .jpg image and store in array
Step2. Reconstruct the image from same array
What I have found is, that the size of new image constructed is less than the original.
I am pasting the code below
public static void main(String[] args) {
BufferedImage sourceImage = null;
try {
sourceImage = ImageIO.read(new File("Sample.jpg"));
} catch (IOException e) {
int type = sourceImage.getType();
int w = sourceImage.getWidth();
int h = sourceImage.getHeight();
byte[] pixels = null;
if (type == BufferedImage.TYPE_3BYTE_BGR) {
System.out.println("type.3byte.bgr");
pixels = (byte[]) sourceImage.getData().getDataElements(0, 0, w, h, null);
try {
BufferedImage edgesImage = new BufferedImage(w, h, BufferedImage.TYPE_3BYTE_BGR);
edgesImage.getWritableTile(0, 0).setDataElements(0, 0, w, h, pixels);
ImageIO.write(edgesImage, "jpg", new File("result.jpg"));
} catch (IOException e) {
Please could any one explain me why is it so?

Answer 1

I am working on a IEEE paper where in I am supposed to achieve a better compression ratios as compared to current JPEG standards. So if only loading and displaying the image results in size reduction and quality too, how do I go ahead with my algorithmI suggest you:
(a) start with images in an uncompressed format such as TIFF, rather than a format which is already lossy (JPEG)
(b) acquire some basic knowledge about JPEG before you attempt to improve on it, and
(c) learn to quote accurately. Otherwise your paper will be refereed out of existence. I didn't say anything about 'loading and displaying the image resulting in size reduction and quality too'. I said 'loading and storing'; and 'change the contents', not 'size reduction and quality too'.
A JPEG load and store operation does not result in a bitwise identical file. Frankly you should already know that.