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Dr. Andrew Greensted
Last modified: 18th November 2009

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Java

Direct Image Buffer Access

Data Buffer structure for BGR

Data Buffer structure for BGR

When working with image processing, it can be handy to have direct access to an image buffer (such as a BufferedImage) that can rendered to a component paint method.

The image to the right shows the data buffer structure for a 2x2 image using BGR (blue, green, red) colour components. The data buffer is one dimensional, each set of 3 pixels encodes consecutive pixels.

The code block below shows how to create a BufferedImage from a byte array. The most important part is the instantiation of the PixelInterleavedSampleModel:

ArgumentDescription
DataBuffer.TYPE_BYTEThe data type of the image buffer elements
widthThe width of the image
heightThe height of the image
3The number of data buffer elements per pixel
3*widthThe number of data buffer elements per line
new int[] {2,1,0}The location of colour components for each pixel

The last argument is quite important as it defines how the colour components are read from the data buffer. In this case the colours are ordered blue, green then red. If you wanted RGB (red, green, blue), the argument would be int[] {0,1,2}.


File Excerpt: createImage.java
int width = 100;
int height = 100;
int numPixels = width * height;
byte[] data = new byte[numPixels];

DataBufferByte dataBuffer = new DataBufferByte(data, data.length);
PixelInterleavedSampleModel sampleModel
   = new PixelInterleavedSampleModel(DataBuffer.TYPE_BYTE, width, height, 3, 3*width, new int[] {2,1,0});

ColorSpace cs = ColorSpace.getInstance(ColorSpace.CS_sRGB);
ColorModel colourModel = new ComponentColorModel(cs, false, false, Transparency.OPAQUE, DataBuffer.TYPE_BYTE);

WritableRaster raster = Raster.createWritableRaster(sampleModel, dataBuffer, new Point(0,0));

BufferedImage image = new BufferedImage(colourModel, raster, false, null);

Once you've got your image, it's easy to use it in a component's paint method. When you alter the data buffer, you just need to call the component's repaint method.

public void paint(Graphics g)
{
   g.drawImage(image, 0, 0, this);
}

Java Primitives

Type Bit Width Minimum Maximum Default
boolean - false true false
byte 8-bit signed integer -(27) -128 27-1 127 0
char 16-bit unicode 2.0 character 0 216-1 65 535 \0000
short 16-bit signed integer -(215) -32 768 215-1 32 767 0
int 32-bit signed integer -(231) -2 147 483 648 231-1 2 147 483 467 0
long 64-bit signed integer -(263) -9 223 372 036 854 775 808 263-1 9 223 372 036 854 775 807 0l
float 32-bit signed floating-point java.lang.Float.NEGATIVE_INFINITY java.lang.Float.POSITIVE_INFINITY 0.0f
double 64-bit signed floating-point java.lang.Double.NEGATIVE_INFINITY java.lang.Double.POSITIVE_INFINITY 0.0d

Time

The maximum time, in ms, that can be stored in different types:

short:215 ms(32 sec 767 ms)
int:231 ms(24 days, 20 hours, 31 minutes, 23 sec 648 ms)
long:263 ms(Years!!)

Set Default GUI Font

The snippet below get be used to set the default Java GUI font. It works, but there may be a better way

javax.swing.plaf.FontUIResource f = new javax.swing.plaf.FontUIResource("Dialog",Font.PLAIN,10);

java.util.Enumeration keys = UIManager.getDefaults().keys();

while (keys.hasMoreElements())
{
  Object key = keys.nextElement();
  Object value = UIManager.get (key);
  if (value instanceof javax.swing.plaf.FontUIResource) UIManager.put (key, f);
}

Jars

File: manifest
Main-Class: MainClass

> jar -cfm stuff.jar manifest -C class stuff

export CLASSPATH="/java/stuff.jar"

> java stuff.MainClass
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