Develop Reference

Why is JPG altered on retrieval? - Java

I am trying to retrieve an jpg image as a BufferedImage then decompose it into a 3D array [RED][GREEN][BLUE] and then turn it back into a BufferedImage and store it under a different file-name. All looks fine to me BUT, when I am trying to reload the 3D array using the new file created I get different values for RGB although the new image looks fine to the naked eye. I did the following.
BufferedImage bi = ImageIO.read(new File("old.jpg"));
int[][][] one = getArray(bi);
save("kite.jpg", one);
BufferedImage bi2 = ImageIO.read(new File("new.jpg"));
int[][][] two = getArray(bi2);
private void save(String destination, int[][][] in) {
try {
BufferedImage out = new BufferedImage(in.length, in[0].length, BufferedImage.TYPE_3BYTE_BGR);
for (int x=0; x<out.getWidth(); x++) {
for (int y = 0; y < out.getHeight(); y++) {
out.setRGB(x, y, new Color(in[x][y][0], in[x][y][1], in[x][y][2]).getRGB());
}
}
File f = new File("name");
ImageIO.write(out, "JPEG", f);
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
so in the example above the values that arrays one and two are holding are different.
I am guessing there is something to do with the different types of retrieving and restoring images? I am trying to figure out what is going on all day but with no luck. Any help appreciated.

Pretty simple:
JPEG is a commonly used method of lossy compression for digital images
(from wikipedia).
Each time the image is compressed, the image is altered to reduce file-size. In fact repeating the steps of decompression and compression for several hundred times alters the image to the point where the entire image turns into a plain gray area in most cases. There are a few compressions that work lossless, but most operation-modes will alter the image.

java - how to make an image using setRGB?

i have 2D array to keep color component value :
p[pixel_value][red]
p[pixel_value][green]
p[pixel_value][blue]
i just dont know how to use them to make an image.
i read about setRGB, what i understand is i should mix all of them to become a RGBArray. then how to make it?
is it any better way to make an image without setRGB ? i need some explanation.

The method setRGB() can be used to set the color of a pixel of an already existing image. You can open an already existing image and set all the pixels of it, using the values stored in your 2D array.
You can do it like this:
BufferedImage img = ImageIO.read(new File("image which you want to change the pixels"));
for(int width=0; width < img.getWidth(); width++)
{
for(int height=0; height < img.getHeight(); height++)
{
Color temp = new Color(p[pixel_value][red], p[pixel_value][green], p[pixel_value][blue]);
img.setRGB(width, height, temp.getRGB());
}
}
ImageIO.write(img, "jpg", new File("where you want to store this new image"));
Like this, you can iterate over all the pixels and set their color accordingly.
NOTE: By doing this, you will lose your original image. This is just a way which I know.

What you need is a BufferedImage. Create a BufferedImage of type TYPE_3BYTE_BGR, if RGB is what you want, with a specified width and height.
QuickFact:
The BufferedImage subclass describes an Image with an accessible
buffer of image data.
Then, call the getRaster() method to get a WritableRaster
QuickFact:
This class extends Raster to provide pixel writing capabilities.
Then, use the setPixel(int x, int y, double[] dArray) method to set the pixels.
Update:
If all you want is to read an image, use the ImageIO.read(File f) method. It will allow you to read an image file in just one method call.
Somewhat SSCCE:
BufferedImage img = null;
try {
img = ImageIO.read(new File("strawberry.jpg"));
} catch (IOException e) {
}

You want to manually set RGB values?
You need to know that since an int is 32bit it contains all 4 rgb values (1 for the transparency).
xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx
^Alpha ^red ^green ^blue
You can accomplish using 4 int values by the use of binary arithmetic:
int rgb = (red << 16) && () (green << 8) & (blue);
bufferedImage.setRGB(x, y, rgb);
IN the above you can add Alpha as well if needed. You just "push" the binary codes into the right places.

Steganography Lsb information hold capacity

I know that using LSB means that u can store messages at around 12% of the image carrier size.
I made a java program that splits a message into n fragments and fills the image carrier with these fragments until the 12 % are all occupied.I do this so that by cropping the image,the message wouldn't get lost.
The problem is that the resulting image is distorted and different from the original image.I thought that if I fill only 12% of the image,more exactly the LSB of the image,the image wouldn't get distorted.
int numHides = imLen/(totalLen*DATA_SIZE); // the number of messages I can store in the image
int offset = 0;
for(int h=0; h < numHides; h++) //hide all frags, numHides times
for(int i=0; i < NUM_FRAGS; i++) {//NUM_FRAGS ..the number of fragments
hideStegoFrag(imBytes, stegoFrags[i], offset);//the method that hides the fragment into the picture starting at the offset position
offset += stegoFrags[i].length*DATA_SIZE;
}
private static boolean hideStegoFrag(byte[] imBytes,byte[] stego,int off){
int offset=off;
for (int i = 0; i < stego.length; i++) { // loop through stego
int byteVal = stego[i];
for(int j=7; j >= 0; j--) { // loop through 8 bits of stego byte
int bitVal = (byteVal >>> j) & 1;
// change last bit of image byte to be the stego bit
imBytes[offset] = (byte)((imBytes[offset] & 0xFE) | bitVal);
offset++;
}
}
return true;
}
The code for transforming the Buffered Image into bits
private static byte[] accessBytes(BufferedImage image)
{
WritableRaster raster = image.getRaster();
DataBufferByte buffer = (DataBufferByte) raster.getDataBuffer();
return buffer.getData();
}
The code that creates the new image with a provided name and the buffered image of the source image
public static boolean writeImageToFile(String imFnm , BufferedImage im){
try {
ImageIO.write(im, "png", new File(imFnm));
} catch (IOException ex) {
Logger.getLogger(MultiSteg.class.getName()).log(Level.SEVERE, null, ex);
}
return true;
}

The output image you have posted is a 16-color paletted image.
The data I am seeing shows that you have actually applied your changes to the palette index, not to the colors of the image. The reason you are seeing the distortion is because of the way the palette is organized, you aren't modifying the LSB of the color, you're modifying the LSB of the index, which could change it to a completely different (and very noticeable, as you can see) color. (Actually, you're modifying the LSB of every other index, the 16-color form is 4 bits per pixel, 2 pixels per byte.)
It looks like you loaded raw image data and didn't decode it in to RGB color information. Your algorithm will only work on raw RGB (or raw grayscale) data; 3 bytes (or 1 for grayscale) per pixel. You need to convert your image to RGB888 or something similar before you operate on it. When you save it, you need to save it in a lossless, full color (unless you actually can fit all your colors in a palette) format too, otherwise you risk losing your information.
Your problem actually doesn't lie in the steganography portion of your program, but in the loading and saving of the image data itself.
When you load the image data, you need to convert it to an RGB format. The most convenient format for your application will be BufferedImage.TYPE_3BYTE_BGR, which stores each pixel as three bytes in blue, green, red order (so your byte array will be B,G,R,B,G,R,B,G,R,...). You can do that like so:
public static BufferedImage loadRgbImage (String filename) {
// load the original image
BufferedImage originalImage = ImageIO.read(filename);
// create buffer for converted image in RGB format
BufferedImage rgbImage = new BufferedImage(originalImage.getWidth(), originalImage.getHeight(), BufferedImage.TYPE_3BYTE_BGR);
// render original image into buffer, changes to destination format
rgbImage.getGraphics().drawImage(originalImage, 0, 0, null);
return rgbImage;
}
If you are frequently working with source images that are already in BGR format anyways, you can make one easy optimization to not convert the image if it's already in the format you want:
public static BufferedImage loadRgbImage (String filename) {
BufferedImage originalImage = ImageIO.read(filename);
BufferedImage rgbImage;
if (originalImage.getType() == BufferedImage.TYPE_3BYTE_BGR) {
rgbImage = originalImage; // no need to convert, just return original
} else {
rgbImage = new BufferedImage(originalImage.getWidth(), originalImage.getHeight(), BufferedImage.TYPE_3BYTE_BGR);
rgbImage.getGraphics().drawImage(originalImage, 0, 0, null);
}
return rgbImage;
}
You can then just use the converted image for all of your operations. Note that the byte array from the converted image will contain 3 * rgbImage.getWidth() * rgbImage.getHeight() bytes.
You shouldn't have to make any changes to your current image saving code; ImageIO will detect that the image is RGB and will write a 24-bit PNG.

Is there a function to sum the rasters of two buffered images?

I'm doing 2D filteing and want to do element by element addition on grayscale BufferedImages. Is there an existing function that will complete this for me or do i need to make one from scrach?
Is there some sort of matrix class that converts a raster to a matrix to simplyfy this problem?
Edit: here is the general gist of it
BufferedImageOp opX = new ConvolveOp(new Kernel(3,3, kernelX));
BufferedImageOp opY = new ConvolveOp(new Kernel(3,3, kernelY));
BufferedImage filtImageX = opX.filter(sourceImage, null);
BufferedImage filtImageY = opY.filter(sourceImage, null);
BufferedImage outputImage = addBufferedImages(filtImageX, filtImageY);
Grayscale Conversion:
public void toGrayscale() {
BufferedImageOp op = new ColorConvertOp(ColorSpace.getInstance(ColorSpace.CS_GRAY), null);
sourceImage = op.filter(sourceImage, null);
}

I am not familiar with any java libs that do that for you.
You can get pixel at [i,j] with: image.getRGB(i, j);
BufferedImage image = ...;
BufferedImage resultImage = ...
int rgb= image.getRGB(i, j);
resultImage.setRGB(i, j, rgb);
You can also convert a buffered image to a byte array [ https://stackoverflow.com/a/7388025/1007845 ].
See this thread: how to convert image to byte array in java? to get a WritableRaster
EDIT:
It seems that WritableRaster might be useful in this case: http://docs.oracle.com/javase/1.4.2/docs/api/java/awt/image/WritableRaster.html
WritableRaster raster = image.getRaster();
for(int h=0;h<height;h++) {
for(int w=0;w<width;w++) {
int colour = 127;
raster.setSample(w,h,0,colour);
}
}

I don't know of a direct way to do this.
But i can suggest a slightly underhanded approach. First, take your two images, and combine them into a single image with two bands. I'm hazy on the details of how to do this. I suspect you will want to create a Raster with a BandedSampleModel, and then blit the contents of the other two images into its DataBuffer. Although it looks like you should be able to create a two-bank DataBuffer which uses the arrays of the source images' (one-banked) DataBuffers as banks, which would avoid copying.
Once you have a two-band image, simply apply a BandCombineOp which sums the bands. You will need to express the summation as a matrix, but that shouldn't be hard. I think it would be [1.0, 1.0],or [0.5, 0.5] if you want to rescale the result.

Turn an array of pixels into an Image object with Java's ImageIO?

I'm currently turning an array of pixel values (originally created with a java.awt.image.PixelGrabber object) into an Image object using the following code:
public Image getImageFromArray(int[] pixels, int width, int height) {
MemoryImageSource mis = new MemoryImageSource(width, height, pixels, 0, width);
Toolkit tk = Toolkit.getDefaultToolkit();
return tk.createImage(mis);
}
Is it possible to achieve the same result using classes from the ImageIO package(s) so I don't have to use the AWT Toolkit?
Toolkit.getDefaultToolkit() does not seem to be 100% reliable and will sometimes throw an AWTError, whereas the ImageIO classes should always be available, which is why I'm interested in changing my method.

You can create the image without using ImageIO. Just create a BufferedImage using an image type matching the contents of the pixel array.
public static Image getImageFromArray(int[] pixels, int width, int height) {
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
WritableRaster raster = (WritableRaster) image.getData();
raster.setPixels(0,0,width,height,pixels);
return image;
}
When working with the PixelGrabber, don't forget to extract the RGBA info from the pixel array before calling getImageFromArray. There's an example of this in the handlepixelmethod in the PixelGrabber javadoc. Once you do that, make sure the image type in the BufferedImage constructor to BufferedImage.TYPE_INT_ARGB.

Using the raster I got an ArrayIndexOutOfBoundsException even when I created the BufferedImage with TYPE_INT_ARGB. However, using the setRGB(...) method of BufferedImage worked for me.

JavaDoc on BufferedImage.getData() says: "a Raster that is a copy of the image data."
This code works for me but I doubt in it's efficiency:
// Получаем картинку из массива.
int[] pixels = new int[width*height];
// Рисуем диагональ.
for (int j = 0; j < height; j++) {
for (int i = 0; i < width; i++) {
if (i == j) {
pixels[j*width + i] = Color.RED.getRGB();
}
else {
pixels[j*width + i] = Color.BLUE.getRGB();
//pixels[j*width + i] = 0x00000000;
}
}
}
BufferedImage pixelImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
pixelImage.setRGB(0, 0, width, height, pixels, 0, width);

I've had good success using java.awt.Robot to grab a screen shot (or a segment of the screen), but to work with ImageIO, you'll need to store it in a BufferedImage instead of the memory image source. Then you can call one static method of ImageIO and save the file. Try something like:
// Capture whole screen
Rectangle region = new Rectangle(Toolkit.getDefaultToolkit().getScreenSize());
BufferedImage capturedImage = new Robot().createScreenCapture(region);
// Save as PNG
File imageFile = new File("capturedImage.png");
ImageIO.write(capturedImage, "png", imageFile);

As this is one of the highest voted question tagged with ImageIO on SO, I think there's still room for a better solution, even if the question is old. :-)
Have a look at the BufferedImageFactory.java class from my open source imageio project at GitHub.
With it, you can simply write:
BufferedImage image = new BufferedImageFactory(image).getBufferedImage();
The other good thing is that this approach, as a worst case, has about the same performance (time) as the PixelGrabber-based examples already in this thread. For most of the common cases (typically JPEG), it's about twice as fast. In any case, it uses less memory.
As a side bonus, the color model and pixel layout of the original image is kept, instead of translated to int ARGB with default color model. This might save additional memory.
(PS: The factory also supports subsampling, region-of-interest and progress listeners if anyone's interested. :-)

I had the same problem of everyone else trying to apply the correct answer of this question, my int array actually get an OutOfboundException where i fixed it adding one more index because the length of the array has to be widht*height*3 after this i could not get the image so i fixed it setting the raster to the image
public static Image getImageFromArray(int[] pixels, int width, int height) {
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
WritableRaster raster = (WritableRaster) image.getData();
raster.setPixels(0,0,width,height,pixels);
image.setData(raster);
return image;
}
And you can see the image if u show it on a label on a jframe like this
JFrame frame = new JFrame();
frame.getContentPane().setLayout(new FlowLayout());
frame.getContentPane().add(new JLabel(new ImageIcon(image)));
frame.pack();
frame.setVisible(true);
setting the image on the imageIcon().
Last advice you can try to change the Bufferedimage.TYPE_INT_ARGB to something else that matches the image you got the array from this type is very important i had an array of 0 and -1 so I used this type BufferedImage.TYPE_3BYTE_BGR