1. Code Samples
  2. Drawing
  3. Clipping Paths

Fade and shape images with soft masks

View as Markdown

DrawingGradientGraphics ContainerPDF

This sample shows how to make parts of an item gradually transparent with a soft mask, the PDF way of masking that keeps both the item and the mask vector. A soft mask is a GraphicsContainer assigned to an item through its SoftMask property. With SoftMaskMethod.Luminosity the brightness of the mask sets the opacity: here a white-to-black gradient fades a photo out to the right. With SoftMaskMethod.Alpha only the transparency of the mask counts and its colours are ignored: here the alpha channel of a PNG gives a second photo the shape of a postage stamp.

Code Snippet

const float width = 800, height = 400, dpi = 72;

using (var venice = new Bitmap("Venice.jpg"))
using (var chicago = new Bitmap("Chicago.jpg"))
using (var stamp = new Bitmap("Stamp.png"))
using (var page = new GraphicsContainer(width, height, dpi, dpi))
using (var fade = new GraphicsContainer(width, height, dpi, dpi))
using (var silhouette = new GraphicsContainer(width, height, dpi, dpi))
{
    venice.Transforms.Resize(360, 360, ResizeInterpolationMode.High, ResizeMode.Fit);
    chicago.Transforms.Resize(360, 360, ResizeInterpolationMode.High, ResizeMode.ImageFill);
    stamp.Transforms.Resize(360, 360, ResizeInterpolationMode.High, ResizeMode.Fit);

    var veniceRect = new RectangleF(20, (height - venice.Height) / 2, venice.Width, venice.Height);
    var stampPosition = new PointF(420, (height - stamp.Height) / 2);

    // Luminosity: white keeps the photo, black hides it, greys in between make it partly transparent.
    using (var graphics = fade.GetGraphics())
    {
        var gradient = new LinearGradientBrush()
        {
            StartPoint = new PointF(veniceRect.Left, 0),
            EndPoint = new PointF(veniceRect.Right, 0),
            ColorStops = new ColorStop[]
            {
                new ColorStop() { Color = RgbColor.White, Position = 0.3f },
                new ColorStop() { Color = RgbColor.Black, Position = 1.0f },
            },
        };

        graphics.FillRectangle(gradient, veniceRect);
    }

    page.Items.Add(new ImageItem()
    {
        Image = venice,
        Position = veniceRect.Location,
        SoftMask = new SoftMask(fade) { Method = SoftMaskMethod.Luminosity },
    });

    // Alpha: only the transparency of the mask counts, the colours of the stamp are ignored.
    using (var graphics = silhouette.GetGraphics())
    {
        graphics.DrawImage(stamp, stampPosition.X, stampPosition.Y);
    }

    page.Items.Add(new ImageItem()
    {
        Image = chicago,
        Position = stampPosition,
        SoftMask = new SoftMask(silhouette) { Method = SoftMaskMethod.Alpha },
    });

    using (var writer = new PdfWriter("ApplySoftMask.pdf"))
    using (var graphics = writer.GetGraphics())
    {
        writer.AddPage(width, height, dpi, dpi);
        graphics.DrawContainer(page, 0, 0);
    }
}

Input

Venice.jpg

Venice.jpg

Chicago.jpg

Chicago.jpg

Stamp.png

Stamp.png

Output

ApplySoftMask.pdf

Download

ApplySoftMask.png

ApplySoftMask.png

Used APIs