code: public static void scaleFit(Bitmap src, Bitmap dest, int clearColor) {
          float ratio = Math.min(dest.getWidth() / (float) src.getWidth(), dest.getHeight() / (float) src.getHeight());
          int newW = (int) (src.getWidth() * ratio);
          int newH = (int) (src.getHeight() * ratio);
          int paddingTop = (dest.getHeight() - (int) (src.getHeight() * ratio)) / 2;
          int paddingLeft = (dest.getWidth() - (int) (src.getWidth() * ratio)) / 2;
  
          scale(src, dest, clearColor, 0, 0, src.getWidth(), src.getHeight(), paddingLeft, paddingTop,
                  newW + paddingLeft,
                  newH + paddingTop);
      }
docs: Scaling src Bitmap to fit and cenetered in dest bitmap. Method keep aspect ratio.
  
  @param src        source bitmap
  @param dest       destination bitmap
  @param clearColor color for clearing dest before drawing