ImageJ is an Open Source application / library that has support for may formats including BMP.
Here is some real code using BMPDecoder from ImageJ:
Here is the license statement.
import java.awt.image.ColorModel;
import java.awt.image.IndexColorModel;
import java.awt.image.MemoryImageSource;
import java.io.IOException;
import java.io.InputStream;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
public class BMPDecoder {
InputStream is;
int curPos = 0;
int bitmapOffset; // starting position of image data
int width; // image width in pixels
int height; // image height in pixels
short bitsPerPixel; // 1, 4, 8, or 24 (no color map)
int compression; // 0 (none), 1 (8-bit RLE), or 2 (4-bit RLE)
int actualSizeOfBitmap;
int scanLineSize;
int actualColorsUsed;
byte r[], g[], b[]; // color palette
int noOfEntries;
byte[] byteData; // Unpacked data
int[] intData; // Unpacked data
boolean topDown;
private int readInt() throws IOException {
int b1 = is.read();
int b2 = is.read();
int b3 = is.read();
int b4 = is.read();
curPos += 4;
return ((b4 << 24) + (b3 << 16) + (b2 << 8) + (b1 << 0));
}
private short readShort() throws IOException {
int b1 = is.read();
int b2 = is.read();
curPos += 2;
return (short) ((b2 << 8) + b1);
}
void getFileHeader() throws IOException, Exception {
// Actual contents (14 bytes):
short fileType = 0x4d42;// always "BM"
int fileSize; // size of file in bytes
short reserved1 = 0; // always 0
short reserved2 = 0; // always 0
fileType = readShort();
if (fileType != 0x4d42)
throw new Exception("Not a BMP file"); // wrong file type
fileSize = readInt();
reserved1 = readShort();
reserved2 = readShort();
bitmapOffset = readInt();
}
void getBitmapHeader() throws IOException {
// Actual contents (40 bytes):
int size; // size of this header in bytes
short planes; // no. of color planes: always 1
int sizeOfBitmap; // size of bitmap in bytes (may be 0: if so,
// calculate)
int horzResolution; // horizontal resolution, pixels/meter (may be 0)
int vertResolution; // vertical resolution, pixels/meter (may be 0)
int colorsUsed; // no. of colors in palette (if 0, calculate)
int colorsImportant; // no. of important colors (appear first in
// palette) (0 means all are important)
int noOfPixels;
size = readInt();
width = readInt();
height = readInt();
planes = readShort();
bitsPerPixel = readShort();
compression = readInt();
sizeOfBitmap = readInt();
horzResolution = readInt();
vertResolution = readInt();
colorsUsed = readInt();
colorsImportant = readInt();
topDown = (height < 0);
if (topDown)
height = -height;
noOfPixels = width * height;
// Scan line is padded with zeroes to be a multiple of four bytes
scanLineSize = ((width * bitsPerPixel + 31) / 32) * 4;
actualSizeOfBitmap = scanLineSize * height;
if (colorsUsed != 0)
actualColorsUsed = colorsUsed;
else
// a value of 0 means we determine this based on the bits per pixel
if (bitsPerPixel < 16)
actualColorsUsed = 1 << bitsPerPixel;
else
actualColorsUsed = 0; // no palette
}
void getPalette() throws IOException {
noOfEntries = actualColorsUsed;
// IJ.write("noOfEntries: " + noOfEntries);
if (noOfEntries > 0) {
r = new byte[noOfEntries];
g = new byte[noOfEntries];
b = new byte[noOfEntries];
int reserved;
for (int i = 0; i < noOfEntries; i++) {
b[i] = (byte) is.read();
g[i] = (byte) is.read();
r[i] = (byte) is.read();
reserved = is.read();
curPos += 4;
}
}
}
void unpack(byte[] rawData, int rawOffset, int bpp, byte[] byteData,
int byteOffset, int w) throws Exception {
int j = byteOffset;
int k = rawOffset;
byte mask;
int pixPerByte;
switch (bpp) {
case 1:
mask = (byte) 0x01;
pixPerByte = 8;
break;
case 4:
mask = (byte) 0x0f;
pixPerByte = 2;
break;
case 8:
mask = (byte) 0xff;
pixPerByte = 1;
break;
default:
throw new Exception("Unsupported bits-per-pixel value: " + bpp);
}
for (int i = 0;;) {
int shift = 8 - bpp;
for (int ii = 0; ii < pixPerByte; ii++) {
byte br = rawData[k];
br >>= shift;
byteData[j] = (byte) (br & mask);
// System.out.println("Setting byteData[" + j + "]=" +
// Test.byteToHex(byteData[j]));
j++;
i++;
if (i == w)
return;
shift -= bpp;
}
k++;
}
}
void unpack24(byte[] rawData, int rawOffset, int[] intData, int intOffset,
int w) {
int j = intOffset;
int k = rawOffset;
int mask = 0xff;
for (int i = 0; i < w; i++) {
int b0 = (((int) (rawData[k++])) & mask);
int b1 = (((int) (rawData[k++])) & mask) << 8;
int b2 = (((int) (rawData[k++])) & mask) << 16;
intData[j] = 0xff000000 | b0 | b1 | b2;
j++;
}
}
void unpack32(byte[] rawData, int rawOffset, int[] intData, int intOffset,
int w) {
int j = intOffset;
int k = rawOffset;
int mask = 0xff;
for (int i = 0; i < w; i++) {
int b0 = (((int) (rawData[k++])) & mask);
int b1 = (((int) (rawData[k++])) & mask) << 8;
int b2 = (((int) (rawData[k++])) & mask) << 16;
int b3 = (((int) (rawData[k++])) & mask) << 24; // this gets
// ignored!
intData[j] = 0xff000000 | b0 | b1 | b2;
j++;
}
}
void getPixelData() throws IOException, Exception {
byte[] rawData; // the raw unpacked data
// Skip to the start of the bitmap data (if we are not already there)
long skip = bitmapOffset - curPos;
if (skip > 0) {
is.skip(skip);
curPos += skip;
}
int len = scanLineSize;
if (bitsPerPixel > 8)
intData = new int[width * height];
else
byteData = new byte[width * height];
rawData = new byte[actualSizeOfBitmap];
int rawOffset = 0;
int offset = (height - 1) * width;
for (int i = height - 1; i >= 0; i--) {
int n = is.read(rawData, rawOffset, len);
if (n < len)
throw new Exception("Scan line ended prematurely after " + n
+ " bytes");
if (bitsPerPixel == 24)
unpack24(rawData, rawOffset, intData, offset, width);
else if (bitsPerPixel == 32)
unpack32(rawData, rawOffset, intData, offset, width);
else
// 8-bits or less
unpack(rawData, rawOffset, bitsPerPixel, byteData, offset,
width);
rawOffset += len;
offset -= width;
}
}
public void read(InputStream is) throws IOException, Exception {
this.is = is;
getFileHeader();
getBitmapHeader();
if (compression != 0)
throw new Exception("Compression not supported");
getPalette();
getPixelData();
}
public MemoryImageSource makeImageSource() {
ColorModel cm;
MemoryImageSource mis;
if (noOfEntries > 0) {
// There is a color palette; create an IndexColorModel
cm = new IndexColorModel(bitsPerPixel, noOfEntries, r, g, b);
} else {
// There is no palette; use the default RGB color model
cm = ColorModel.getRGBdefault();
}
// Create MemoryImageSource
if (bitsPerPixel > 8) {
// use one int per pixel
mis = new MemoryImageSource(width, height, cm, intData, 0, width);
} else {
// use one byte per pixel
mis = new MemoryImageSource(width, height, cm, byteData, 0, width);
}
return mis; // this can be used by Component.createImage()
}
public static void main(String[] aqgs) {
BMPDecoder bd = new BMPDecoder();
try {
bd.read(BMPDecoder.class.getResourceAsStream("bmp.bmp"));
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
JFrame jf = new JFrame();
JLabel jl = new JLabel();
ImageIcon ii = new ImageIcon( jl.createImage(bd.makeImageSource()));
jl.setIcon(ii);
jf.add(jl);
jf.pack();
jf.setVisible(true);
}
}