实现手写图片，将图片转化为字符串以及字符串转化为图片，减小发送内容大小

<pre name="code" class="java">	/**
	 * bitmap转为base64
	 * @param bitmap
	 * @return
	 */
	public static String bitmapToBase64(Bitmap bitmap) {

		String result = null;
		ByteArrayOutputStream baos = null;
		try {
			if (bitmap != null) {
				baos = new ByteArrayOutputStream();
				bitmap.compress(Bitmap.CompressFormat.JPEG, 100, baos);

				baos.flush();
				baos.close();

				byte[] bitmapBytes = baos.toByteArray();
				result = Base64.encodeToString(bitmapBytes, Base64.DEFAULT);
			}
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				if (baos != null) {
					baos.flush();
					baos.close();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		return result;
	}

	/**
	 * base64转为bitmap
	 * @param base64Data
	 * @return
	 */
	public static Bitmap base64ToBitmap(String base64Data) {
		byte[] bytes = Base64.decode(base64Data, Base64.DEFAULT);
		return BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
	}

android bitmap和base64之间的转换