private void DrawingArea_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
            if (sender == null || !(sender is Canvas))
            {
                throw new ArgumentException("expected only Canvas", "sender");
            }

            //Status = "ready";

            var canvas = (Canvas)sender;

            if (!keyIsDown)
            {
                return;
            }

            switch (tool)
            {
            case Tools.Filtering:
            {
                ReinitializeMask();
                DrawingBrush.Visibility = Visibility.Hidden;
            } break;

            case Tools.Line:
            {
                double x = e.GetPosition(canvas).X;
                double y = e.GetPosition(canvas).Y;

                int startX = (int)currentLineStart.X;
                int startY = (int)currentLineStart.Y;
                int endX   = (int)x;
                int endY   = (int)y;

                bitmapArray.CopyArea(bitmapArrayTemp);
                if (bitmapArrayWithoutLines == null)
                {
                    bitmapArrayWithoutLines = new FastBitmapArray(bitmapArray);
                }

                if (multisamplingForNewLines)
                {
                    int scaling = 2;
                    bitmapArrayWithoutLines = bitmapArrayWithoutLines.ScaleUp(scaling);

                    var l = new Line(scaling * startX, scaling * startY, scaling * endX, scaling * endY,
                                     lineColor.ScR, lineColor.ScG, lineColor.ScB, scaling * (int)lineThickness);

                    bitmapArrayWithoutLines.DrawLine(l);
                    bitmapArrayWithoutLines = bitmapArrayWithoutLines.ScaleDown(scaling);

                    SetBitmapArray(bitmapArrayWithoutLines);
                }
                else
                {
                    var l = new Line(startX, startY, endX, endY,
                                     lineColor.ScR, lineColor.ScG, lineColor.ScB, (int)lineThickness);

                    bitmapArray.DrawLine(l);
                    bitmapArray.RefreshBitmap(Mask.Disabled);

                    Lines.Add(l);
                }

                bitmapArrayTemp = null;

                //LineAdd.IsEnabled = true;
                //LineUpdate.IsEnabled = true;
            } break;
            }

            if (canvas.IsMouseCaptured)
            {
                canvas.ReleaseMouseCapture();
            }

            if (keyIsDown)
            {
                keyIsDown = false;
            }
        }