Android : save a Bitmap to bmp file format

Question

I have a Bitmap in memory and I need to save it in a bmp file (using the bmp file format).

Is there any way to do it on Android ?

(I read a lot of post sugg

Answer 1

Note, the code above is very slow. I've found that to optimize the code above it's necessary to make a byte array to store all the data before you put it. Of course, I was working in Xamarin C# so maybe that's why. Anyway, here's my Xamarin code in case anyone has the same problem.

      public class AndroidBmpUtil
        {

            private static int BMP_WIDTH_OF_TIMES = 4;
            private static 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 byte[] ConvertAndroidBitmapByteArray(Bitmap orgBitmap, String filePath)
            {
                if (orgBitmap == null)
                {
                    return null;
                }

                if (filePath == null)
                {
                    return null;
                }

                //image size
                int width = orgBitmap.Width;
                int height = orgBitmap.Height;

                //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;
                bool 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((sbyte)0x42);
                buffer.Put((sbyte)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;

                // This while loop is a lengthy process
                // Puts take a while so only do one by creating a big array called final
                byte[] final = new byte[0];
                while (row > 0)
                {
                    // This array is also used to cut down on time of puts
                    byte[] b = new byte[(endPosition - startPosition)*3];
                    int counter = 0;
                    for (int i = startPosition; i < endPosition; i++)
                    {

                        b[counter] = (byte)((pixels[i] & 0x000000FF));
                        b[counter + 1] = (byte)((pixels[i] & 0x0000FF00) >> 8);
                        b[counter + 2] = (byte)((pixels[i] & 0x00FF0000) >> 16);
                        counter += 3;
                    }
                    int finalPriorLength = final.Length;
                    Array.Resize(ref final, finalPriorLength + b.Length);
                    Array.Copy(b, 0, final, finalPriorLength, b.Length);

                    if (hasDummy)
                    {
                        finalPriorLength = final.Length;
                        Array.Resize(ref final, finalPriorLength + dummyBytesPerRow.Length);
                        Array.Copy(dummyBytesPerRow, 0, final, finalPriorLength, dummyBytesPerRow.Length);
                    }
                    row--;
                    endPosition = startPosition;
                    startPosition = startPosition - col;
                }
                buffer.Put(final);
                buffer.Rewind();

                IntPtr classHandle = JNIEnv.FindClass("java/nio/ByteBuffer");
                IntPtr methodId = JNIEnv.GetMethodID(classHandle, "array", "()[B");
                IntPtr resultHandle = JNIEnv.CallObjectMethod(buffer.Handle, methodId);
                byte[] result = JNIEnv.GetArray(resultHandle);
                JNIEnv.DeleteLocalRef(resultHandle);

                return result;
            }

            /**
             * Write integer to little-endian
             * @param value
             * @return
             * @throws IOException
             */
            private static byte[] writeInt(int value)
            {
                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)
            {
                byte[] b = new byte[2];

                b[0] = (byte)(value & 0x00FF);
                b[1] = (byte)((value & 0xFF00) >> 8);

                return b;
            }
        }
    }

To use it here's the calling code:

using (FileStream outStream = new    FileStream(@yourFilePath, FileMode.Create))
{
    Bitmap Signature = Bitmap.CreateBitmap(user defined values...); 
    byte[] buffer = AndroidBmpUtil.ConvertAndroidBitmapByteArray(Signature, @yourFilePath); 

    // Actually create the file                                 
    outStream.Write(buffer, 0, buffer.Length);
}