jpeg manipulation using java

[vbnandu86]

some of my friends have planned to do A F.R. project using a simple algorithm Eigen Faces usnig Principal Component Analysis( by turk and Petland )

I have used the following code to extract pixel values from a Jpeg image , but it gives me negative values wen i print the pixel values!!
I dont know if I can continue with negative values for further computation like finding the co-variance matrix ...eigen vectors etc... ...
If u know anything please reply.....

private byte bytes[]=null;
private double doubles[] = null;
private String filename=null;
private int height = 0;
private int width = 0;
 
 
private void readImage() throws FileNotFoundException, IOException {
 
FileInputStream fIn = new FileInputStream(filename);
JPEGImageDecoder jpeg_decode = JPEGCodec.createJPEGDecoder(fIn);
BufferedImage image = jpeg_decode.decodeAsBufferedImage();
 
 
width = image.getWidth();
height = image.getHeight();
 
int[] rgbdata = new int[width * height];
 
image.getRGB(0,0,width,height,rgbdata,0,width);
 
 
bytes = new byte[rgbdata.length];
doubles = new double[rgbdata.length];
 
for (int i = 0; i < bytes.length; i++) {
bytes = (byte) (rgbdata & 0xFF);
doubles = (double)(rgbdata);
}

[BigDaddyLH]

1. I think you are using old code for reading a jpeg that is not part of the J2SE. You can now use class javax.imageio.ImageIO:

BufferedImage image = ImageIO.read(url_or_file_etc...);

2. Your code doesn't compile (rgbdata is an array so you can't write "rgbdata & 0xFF"), but I'm guessing your problem is the following. You have some data in a byte. In Java bytes are always signed, so they hold a value in the range [-128,127]. Nevertheless, most programmers use them as though they held a value in the range [0,255]. To obtain this "unsigned" value, do the following:

byte b = ...
int value = b & 0xff;

I hope the problem doesn't really have to do with your algorithm, which went flying over my head.

If you still have a problem, post a SSCCE: http://mindprod.com/jgloss/sscce.html

[vbnandu86]

Thanks!!!!!!!!!!! i'll be back if i have any more queries

[RedSon]

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