@Override
	public void surfaceChanged(SurfaceHolder holder, int format, int width,
			int height) {

		mParameters = mCamera.getParameters();
		
		Size size = mParameters.getPictureSize();
		
		List<Size> sizes = mParameters.getSupportedPreviewSizes();
	        Size optimalSize = getOptimalPreviewSize(
	                sizes, (double) size.width / size.height);
	        if (optimalSize != null) {
	            mParameters.setPreviewSize(optimalSize.width, optimalSize.height);
	    }
	      
		setPictureSize(mParameters);
		
		mCamera.setParameters(mParameters);
		
	}
 

private Size getOptimalPreviewSize(List<Size> sizes, double targetRatio) {
	        final double ASPECT_TOLERANCE = 0.05;
	        if (sizes == null) return null;

	        Size optimalSize = null;
	        double minDiff = Double.MAX_VALUE;

	        // Because of bugs of overlay and layout, we sometimes will try to
	        // layout the viewfinder in the portrait orientation and thus get the
	        // wrong size of mSurfaceView. When we change the preview size, the
	        // new overlay will be created before the old one closed, which causes
	        // an exception. For now, just get the screen size
	        Display display = ((Activity) mContext).getWindowManager().getDefaultDisplay();
	        int targetHeight = Math.min(display.getHeight(), display.getWidth());

	        if (targetHeight <= 0) {
	            // We don't know the size of SurefaceView, use screen height
	            WindowManager windowManager = (WindowManager)
	            		mContext.getSystemService(Context.WINDOW_SERVICE);
	            targetHeight = windowManager.getDefaultDisplay().getHeight();
	        }
	        // Try to find an size match aspect ratio and size
	        for (Size size : sizes) {
	            double ratio = (double) size.width / size.height;
	            if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) continue;
	            if (Math.abs(size.height - targetHeight) < minDiff) {
	                optimalSize = size;
	                minDiff = Math.abs(size.height - targetHeight);
	            }
	        }
	        // Cannot find the one match the aspect ratio, ignore the requirement
	        if (optimalSize == null) {
	            Log.v(TAG, "No preview size match the aspect ratio");
	            minDiff = Double.MAX_VALUE;
	            for (Size size : sizes) {
	                if (Math.abs(size.height - targetHeight) < minDiff) {
	                    optimalSize = size;
	                    minDiff = Math.abs(size.height - targetHeight);
	                }
	            }
	        }
	        return optimalSize;
	    }