Java Greyscale buffered image

Question

So I have a byte array representing pixel data (8bit grayscale). No header. No nothing. Just the data. I want to create a buffered image from this data. I did

image = new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
image.getRaster().setDataElements(0, 0, w, h, data);
this.x = w;
this.y = h;
scalemode=false;
exactmode=true;

where w is just width in pixel,h is height in pixel,data is the byte array and image is BufferedImage

here is my paint method

 protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;

        int rx = (this.getWidth() - x) / 2;
        int ry = (this.getHeight() - y) / 2;

        g2d.drawImage(image, rx, ry,x,y, null);
    }

I, however, get this image (the real image is a fingerprint, which is mostly white pixel)

What went wrong? I tried saving the data as is and then viewing it in Photoshop. The data is fine.

[edit] Never mind this problem. I fucked up in other part of the code and was not aware. Thank you for all inputs though

What type is data?

MadProgrammer
– MadProgrammer

2015-08-20 04:14:23 +00:00
Commented Aug 20, 2015 at 4:14 — MadProgrammer
– MadProgrammer, Commented Aug 20, 2015 at 4:14
data is byte[] 1byte = 1pixel

mimimi
– mimimi

2015-08-20 04:15:09 +00:00
Commented Aug 20, 2015 at 4:15 — mimimi
– mimimi, Commented Aug 20, 2015 at 4:15
draw every byte on each pixel...

Martin Frank
– Martin Frank

2015-08-20 05:27:22 +00:00
Commented Aug 20, 2015 at 5:27 — Martin Frank
– Martin Frank, Commented Aug 20, 2015 at 5:27
Is that 1 pixel border part of the image?

Harald K
– Harald K

2015-08-20 06:42:39 +00:00
Commented Aug 20, 2015 at 6:42 — Harald K
– Harald K, Commented Aug 20, 2015 at 6:42
no border is not the part of the image

mimimi
– mimimi

2015-08-20 08:15:02 +00:00
Commented Aug 20, 2015 at 8:15 — mimimi
– mimimi, Commented Aug 20, 2015 at 8:15

Harald K · Accepted Answer · 2015-08-20 06:44:14Z

2

It's hard to know exactly what is wrong, as you haven't posted enough information. We don't know w, h or what information is in your data. We don't know what the image should look like.

However, here's some code that does pretty much exactly what you are doing, and it works for me:

// Set up h/w and backing data
int w = 300;
int h = 200;
byte[] data = new byte[w * h];

// Create a smooth gradient
for (int y = 0; y < h; y++) {
    int off = y * w;

    for (int x = 0; x < w; x++) {
        data[off + x] = (byte) (Math.round((x / (double) w) * 127) 
                              + Math.round((y / (double) h) * 127));
    }
}

// Create BufferedImage from data
final BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
image.getRaster().setDataElements(0, 0, w, h, data);

// Show it all in a window
SwingUtilities.invokeLater(new Runnable() {
    @Override
    public void run() {
        JFrame frame = new JFrame(getClass().getSimpleName());
        frame.add(new JLabel(new ImageIcon(image)));

        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
});

Here is the result:

answered Aug 20, 2015 at 6:44

Harald K

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4 Comments

Martin Frank Over a year ago

the image provided by Green Melon really looks like it has incorrect values for width and height..

mimimi Over a year ago

I just tried testing the whole thing, and I found that if the image is created in a nice single main thread, the image is fine. However, when I created the image in mouse event listener thread, the image becomes garbled! I just realized that the data (the byte array) is already messed up so there is no way I can get it right. Do you know what might be the problem in reading from BufferedinputStream from listener thread? I used the code from here. Particularly, the upImg method

Harald K Over a year ago

@GreenMellon Ok. No problem. :-) Reading from streams should work just as normal from the listener thread, but for the sake of a responsive UI it is strongly discouraged. Generally, all I/O should be done on a background thread. Anyway, glad you figured it out!

mimimi Over a year ago

Turned out that the fingerprinting module I was working with actually modify its image buffer when it convert image to signature file. I am totally lost as to why (small memory?). So it had nothing to do with Java. Thanks for the tip though

Martin Frank · Accepted Answer · 2015-08-20 05:47:37Z

1

draw every byte on each pixel...

BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
for (int dy = 0; dy < h; dy ++){
    for(int dx = 0; dx < w; dx ++){
        int index = dy*w + dx;
        int rgb = data[index];
        rgb = rgb << 24 & 0xFFFF; //BufferedImage.TYPE_BYTE_GRAY consideres only the red-channel;
        //rgb = 00 data[index] FF FF
        image.setRGB(dx,dy,rgb);
        }
    }
}

answered Aug 20, 2015 at 5:47

Martin Frank

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Comments

Martin Frank · Accepted Answer · 2015-08-20 05:49:25Z

-1

you didn't set up your Buffer properly...

byte[] data = ... 
DataBufferByte db = new DataBufferByte(data, w*h);
image.getRaster().setDataElements(0, 0, w, h, db );

see http://docs.oracle.com/javase/7/docs/api/java/awt/image/WritableRaster.html#setDataElements%28int,%20int,%20java.lang.Object%29

answered Aug 20, 2015 at 5:49

Martin Frank

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6 Comments

Harald K Over a year ago

The method you are looking for is setDataElements(x, y, w, h, data). And to quote the docs: "Sets the data for a rectangle of pixels from a primitive array of type TransferType" (emphasis mine). This answer is clearly incorrect. The OP's code is fine in this regard.

Martin Frank Over a year ago

@haraldK yes, read on and you'll find " For image data supported by the Java 2D API, this will be one of DataBuffer.TYPE_BYTE, DataBuffer.TYPE_USHORT, DataBuffer.TYPE_INT, DataBuffer.TYPE_SHORT, DataBuffer.TYPE_FLOAT, or DataBuffer.TYPE_DOUBLE"... so where's the error?

Harald K Over a year ago

You seem to think that DataBuffer.TYPE_BYTE == DataBufferByte. It isn't. A "primitive array of type DataBuffer.TYPE_BYTE" simply means byte[].

Martin Frank Over a year ago

well, no that's now what i was thinking ^ ^ (DataBufferByte.getType() would return DataBuffer.TYPE_BYTE - but that's leading to no-where)...i'll aprechiate your example and accept that your code is working. As mentioned in an comment in your example i guess the OP has merely problems with not knowing width/height... @haraldK thanks for providing a good example...

Harald K Over a year ago

I think so too. That is why I ask about the border. And for the record, your code above will crash at runtime, with the following exception: java.lang.ClassCastException: java.awt.image.DataBufferByte cannot be cast to [B. ;-)

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