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Java Tip 60: Saving bitmap files in Java
A tutorial -- including all the code you need to write a bitmap file from an image object
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Page 2 of 3
Section 3: Image
In the 24-bit format, each pixel in the image is represented by a series of three bytes of RGB stored as BRG. Each scan line
is padded to an even 4-byte boundary. To complicate the process a little bit more, the image is stored from bottom to top,
meaning that the first scan line is the last scan line in the image. The following figure shows both headers (BITMAPHEADER) and (BITMAPINFOHEADER) and part of the image. Each section is delimited by a vertical bar:
0000000000 4D42 B536 0002 0000 0000 0036 0000 | 0028 0000000020 0000 0107 0000 00E0 0000 0001 0018 0000 0000000040 0000 B500 0002 0EC4 0000 0EC4 0000 0000 0000000060 0000 0000 0000 | FFFF FFFF FFFF FFFF FFFF 0000000100 FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF *
Now, on to the code
Now that we know all about the structure of a 24-bit bitmap file, here's what you've been waiting for: the code to write a bitmap file from an image object.
import java.awt.*;
import java.io.*;
import java.awt.image.*;
public class BMPFile extends Component {
//--- Private constants
private final static int BITMAPFILEHEADER_SIZE = 14;
private final static int BITMAPINFOHEADER_SIZE = 40;
//--- Private variable declaration
//--- Bitmap file header
private byte bitmapFileHeader [] = new byte [14];
private byte bfType [] = {'B', 'M'};
private int bfSize = 0;
private int bfReserved1 = 0;
private int bfReserved2 = 0;
private int bfOffBits = BITMAPFILEHEADER_SIZE + BITMAPINFOHEADER_SIZE;
//--- Bitmap info header
private byte bitmapInfoHeader [] = new byte [40];
private int biSize = BITMAPINFOHEADER_SIZE;
private int biWidth = 0;
private int biHeight = 0;
private int biPlanes = 1;
private int biBitCount = 24;
private int biCompression = 0;
private int biSizeImage = 0x030000;
private int biXPelsPerMeter = 0x0;
private int biYPelsPerMeter = 0x0;
private int biClrUsed = 0;
private int biClrImportant = 0;
//--- Bitmap raw data
private int bitmap [];
//--- File section
private FileOutputStream fo;
//--- Default constructor
public BMPFile() {
}
public void saveBitmap (String parFilename, Image parImage, int
parWidth, int parHeight) {
try {
fo = new FileOutputStream (parFilename);
save (parImage, parWidth, parHeight);
fo.close ();
}
catch (Exception saveEx) {
saveEx.printStackTrace ();
}
}
/*
* The saveMethod is the main method of the process. This method
* will call the convertImage method to convert the memory image to
* a byte array; method writeBitmapFileHeader creates and writes
* the bitmap file header; writeBitmapInfoHeader creates the
* information header; and writeBitmap writes the image.
*
*/
private void save (Image parImage, int parWidth, int parHeight) {
try {
convertImage (parImage, parWidth, parHeight);
writeBitmapFileHeader ();
writeBitmapInfoHeader ();
writeBitmap ();
}
catch (Exception saveEx) {
saveEx.printStackTrace ();
}
}
/*
* convertImage converts the memory image to the bitmap format (BRG).
* It also computes some information for the bitmap info header.
*
*/
private boolean convertImage (Image parImage, int parWidth, int parHeight) {
int pad;
bitmap = new int [parWidth * parHeight];
PixelGrabber pg = new PixelGrabber (parImage, 0, 0, parWidth, parHeight,
bitmap, 0, parWidth);
try {
pg.grabPixels ();
}
catch (InterruptedException e) {
e.printStackTrace ();
return (false);
}
pad = (4 - ((parWidth * 3) % 4)) * parHeight;
biSizeImage = ((parWidth * parHeight) * 3) + pad;
bfSize = biSizeImage + BITMAPFILEHEADER_SIZE +
BITMAPINFOHEADER_SIZE;
biWidth = parWidth;
biHeight = parHeight;
return (true);
}
/*
* writeBitmap converts the image returned from the pixel grabber to
* the format required. Remember: scan lines are inverted in
* a bitmap file!
*
* Each scan line must be padded to an even 4-byte boundary.
*/
private void writeBitmap () {
int size;
int value;
int j;
int i;
int rowCount;
int rowIndex;
int lastRowIndex;
int pad;
int padCount;
byte rgb [] = new byte [3];
size = (biWidth * biHeight) - 1;
pad = 4 - ((biWidth * 3) % 4);
if (pad == 4) // <==== Bug correction
pad = 0; // <==== Bug correction
rowCount = 1;
padCount = 0;
rowIndex = size - biWidth;
lastRowIndex = rowIndex;
try {
for (j = 0; j < size; j++) {
value = bitmap [rowIndex];
rgb [0] = (byte) (value & 0xFF);
rgb [1] = (byte) ((value >> 8) & 0xFF);
rgb [2] = (byte) ((value >> 16) & 0xFF);
fo.write (rgb);
if (rowCount == biWidth) {
padCount += pad;
for (i = 1; i <= pad; i++) {
fo.write (0x00);
}
rowCount = 1;
rowIndex = lastRowIndex - biWidth;
lastRowIndex = rowIndex;
}
else
rowCount++;
rowIndex++;
}
//--- Update the size of the file
bfSize += padCount - pad;
biSizeImage += padCount - pad;
}
catch (Exception wb) {
wb.printStackTrace ();
}
}
/*
* writeBitmapFileHeader writes the bitmap file header to the file.
*
*/
private void writeBitmapFileHeader () {
try {
fo.write (bfType);
fo.write (intToDWord (bfSize));
fo.write (intToWord (bfReserved1));
fo.write (intToWord (bfReserved2));
fo.write (intToDWord (bfOffBits));
}
catch (Exception wbfh) {
wbfh.printStackTrace ();
}
}
/*
*
* writeBitmapInfoHeader writes the bitmap information header
* to the file.
*
*/
private void writeBitmapInfoHeader () {
try {
fo.write (intToDWord (biSize));
fo.write (intToDWord (biWidth));
fo.write (intToDWord (biHeight));
fo.write (intToWord (biPlanes));
fo.write (intToWord (biBitCount));
fo.write (intToDWord (biCompression));
fo.write (intToDWord (biSizeImage));
fo.write (intToDWord (biXPelsPerMeter));
fo.write (intToDWord (biYPelsPerMeter));
fo.write (intToDWord (biClrUsed));
fo.write (intToDWord (biClrImportant));
}
catch (Exception wbih) {
wbih.printStackTrace ();
}
}
/*
*
* intToWord converts an int to a word, where the return
* value is stored in a 2-byte array.
*
*/
private byte [] intToWord (int parValue) {
byte retValue [] = new byte [2];
retValue [0] = (byte) (parValue & 0x00FF);
retValue [1] = (byte) ((parValue >> 8) & 0x00FF);
return (retValue);
}
/*
*
* intToDWord converts an int to a double word, where the return
* value is stored in a 4-byte array.
*
*/
private byte [] intToDWord (int parValue) {
byte retValue [] = new byte [4];
retValue [0] = (byte) (parValue & 0x00FF);
retValue [1] = (byte) ((parValue >> 8) & 0x000000FF);
retValue [2] = (byte) ((parValue >> 16) & 0x000000FF);
retValue [3] = (byte) ((parValue >> 24) & 0x000000FF);
return (retValue);
}
}
Conclusion
That's all there is to it. I'm sure you'll find this class very useful, since, as of JDK 1.1.6, Java doesn't support saving images in any of the popular formats. JDK 1.2 will offer support for creating JPEG images, but not support for bitmaps. So this class will still fill a gap in JDK 1.2.
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ye, you absolutly right! There is some bug in code!By Anonymous on February 6, 2010, 2:37 pmye, you absolutly right! There is some bug in code!
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Does not work with windows image fax viewerBy Anonymous on October 23, 2008, 8:42 amHi, But unfortunately, the BMP drawn using this code does not open up with windows image and fax viewer in Windows XP. Not very sure of the reasons...I am...
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