Java/SWT displaying an 8bit grayscaling Image from a byte array

Question

I'm building a GUI with the Eclipse Window Builder Editor. I've made a Composite with a Gridlayout and have put a Label in there. Some method from another class generates a raw 8 bit 1280x1024 grayscale image which is saved in a byte array. This is how I generate my ImageData, etc in the mainMethod :

Color white = display.getSystemColor(SWT.COLOR_WHITE);
Color black = display.getSystemColor(SWT.COLOR_BLACK);

PaletteData palette = new PaletteData( 255, 255, 255 );

imgData = new ImageData(1280, 1024, 8, palette);

imgLabel = new Label(composite_3, SWT.NONE);
imgLabel.setImage(null);
imgLabel.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true, 1, 1));

I'm still having problems to understand what exactly I should do with the PaletteData as I don't need colours anyway. (Color)Depth should be 8 because I want it to have 255 grayvalues?

And this is my setImg method which gets called from another Thread as soon as the byte[] is filled with data:

public static void setImg(final byte[] b) {
    Display.getDefault().syncExec( new Runnable() {
        @Override
        public void run() {
            imgData.setPixels(0, 0, 1280, b, 0);
            img = new Image(Display.getCurrent(), imgData);
            Image grayImg = new Image(Display.getCurrent(), img, SWT.IMAGE_GRAY);
            imgLabel.setImage(img);

//              img.dispose();
        }
    });
}

I've tried

imgLabel.setImage(img);

and

imgLabel.setImage(grayImg);

Ok the first line now displays correctly... It seems that I only can set 1 line of pixels with imgData.setPixels(...) which is kind of useless imo or am I doing something else wrong?

score 0 · Accepted Answer · answered Apr 04 '13 at 07:54

Your PaletteData uses the constructor for a direct palette. I guess that what You want is the constructor for an indexed palette. See also here and here for more explanation.

The following code snippet shows

how to create a grey scale palette using an indexed palette

how to set the image as a whole (not line by line)

// pixel depth will be 8-bit, so there is space for 256 different (grey) values
RGB[] rgb = new RGB[256];

// build grey scale palette: 256 different grey values are generated. 
for (int i = 0; i < 256; i++) {
    rgb[i] = new RGB(i, i, i);
}

// Construct a new indexed palette given an array of RGB values.
PaletteData paletteData = new PaletteData(rgb);

// create an image with given dimensions, depth and color palette
ImageData imageData = new ImageData(1280, 1024, 8, paletteData);

// data represents the pixels of the image. This corresponds to 'b' in Your code
imageData.data = b;

// note that there are also other 'Image', e.g. java.awt.Image
org.eclipse.swt.graphics.Image image = new Image(Display.getCurrent(), imageData);

// paint
imgLabel.setImage(img);

// release operating system resources corresponding to the image
image.dispose();

NOTE: I tried an example with Your PaletteData, e.g.

    PaletteData palette = new PaletteData( 255, 255, 255 );

and it worked in the sense that it showed some grey scale pictures (a video actually). However, the indexed version used in given code snippet was much more eye friendly. Have a look at the first link provided above. It gives a good explanation of the difference between indexed and direct color palette.

Java/SWT displaying an 8bit grayscaling Image from a byte array

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