https://stackoverflow.com/questions/22909429
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Here is my current solution. It is derived from this source : https://github.com/ultrakain/AndroidBitmapUtil (thanks to ultrakain and @Francescoverheye )
I just fix a little bug in computation of the dummy bytes that must be added to each row (so that the length of each row in bytes is a multiple of 4 (as required by the bmp format specifications).
I also made some changes to improve the performances.
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import android.graphics.Bitmap;
import android.util.Log;
public class AndroidBmpUtil {
private static final int BMP_WIDTH_OF_TIMES = 4;
private static final int BYTE_PER_PIXEL = 3;
/**
* Android Bitmap Object to Window's v3 24bit Bmp Format File
* @param orgBitmap
* @param filePath
* @return file saved result
*/
public static boolean save(Bitmap orgBitmap, String filePath) throws IOException {
long start = System.currentTimeMillis();
if(orgBitmap == null){
return false;
}
if(filePath == null){
return false;
}
boolean isSaveSuccess = true;
//image size
int width = orgBitmap.getWidth();
int height = orgBitmap.getHeight();
//image dummy data size
//reason : the amount of bytes per image row must be a multiple of 4 (requirements of bmp format)
byte[] dummyBytesPerRow = null;
boolean hasDummy = false;
int rowWidthInBytes = BYTE_PER_PIXEL * width; //source image width * number of bytes to encode one pixel.
if(rowWidthInBytes%BMP_WIDTH_OF_TIMES>0){
hasDummy=true;
//the number of dummy bytes we need to add on each row
dummyBytesPerRow = new byte[(BMP_WIDTH_OF_TIMES-(rowWidthInBytes%BMP_WIDTH_OF_TIMES))];
//just fill an array with the dummy bytes we need to append at the end of each row
for(int i = 0; i < dummyBytesPerRow.length; i++){
dummyBytesPerRow[i] = (byte)0xFF;
}
}
//an array to receive the pixels from the source image
int[] pixels = new int[width * height];
//the number of bytes used in the file to store raw image data (excluding file headers)
int imageSize = (rowWidthInBytes+(hasDummy?dummyBytesPerRow.length:0)) * height;
//file headers size
int imageDataOffset = 0x36;
//final size of the file
int fileSize = imageSize + imageDataOffset;
//Android Bitmap Image Data
orgBitmap.getPixels(pixels, 0, width, 0, 0, width, height);
//ByteArrayOutputStream baos = new ByteArrayOutputStream(fileSize);
ByteBuffer buffer = ByteBuffer.allocate(fileSize);
/**
* BITMAP FILE HEADER Write Start
**/
buffer.put((byte)0x42);
buffer.put((byte)0x4D);
//size
buffer.put(writeInt(fileSize));
//reserved
buffer.put(writeShort((short)0));
buffer.put(writeShort((short)0));
//image data start offset
buffer.put(writeInt(imageDataOffset));
/** BITMAP FILE HEADER Write End */
//*******************************************
/** BITMAP INFO HEADER Write Start */
//size
buffer.put(writeInt(0x28));
//width, height
//if we add 3 dummy bytes per row : it means we add a pixel (and the image width is modified.
buffer.put(writeInt(width+(hasDummy?(dummyBytesPerRow.length==3?1:0):0)));
buffer.put(writeInt(height));
//planes
buffer.put(writeShort((short)1));
//bit count
buffer.put(writeShort((short)24));
//bit compression
buffer.put(writeInt(0));
//image data size
buffer.put(writeInt(imageSize));
//horizontal resolution in pixels per meter
buffer.put(writeInt(0));
//vertical resolution in pixels per meter (unreliable)
buffer.put(writeInt(0));
buffer.put(writeInt(0));
buffer.put(writeInt(0));
/** BITMAP INFO HEADER Write End */
int row = height;
int col = width;
int startPosition = (row - 1) * col;
int endPosition = row * col;
while( row > 0 ){
for(int i = startPosition; i < endPosition; i++ ){
buffer.put((byte)(pixels[i] & 0x000000FF));
buffer.put((byte)((pixels[i] & 0x0000FF00) >> 8));
buffer.put((byte)((pixels[i] & 0x00FF0000) >> 16));
}
if(hasDummy){
buffer.put(dummyBytesPerRow);
}
row--;
endPosition = startPosition;
startPosition = startPosition - col;
}
FileOutputStream fos = new FileOutputStream(filePath);
fos.write(buffer.array());
fos.close();
Log.v("AndroidBmpUtil" ,System.currentTimeMillis()-start+" ms");
return isSaveSuccess;
}
/**
* Write integer to little-endian
* @param value
* @return
* @throws IOException
*/
private static byte[] writeInt(int value) throws IOException {
byte[] b = new byte[4];
b[0] = (byte)(value & 0x000000FF);
b[1] = (byte)((value & 0x0000FF00) >> 8);
b[2] = (byte)((value & 0x00FF0000) >> 16);
b[3] = (byte)((value & 0xFF000000) >> 24);
return b;
}
/**
* Write short to little-endian byte array
* @param value
* @return
* @throws IOException
*/
private static byte[] writeShort(short value) throws IOException {
byte[] b = new byte[2];
b[0] = (byte)(value & 0x00FF);
b[1] = (byte)((value & 0xFF00) >> 8);
return b;
}
}
