Draw text on an image in C# · oneimage cookbook

Add the RecursiveAI.OneImage.Text package, load a font file into a FontCollection, and call DrawText with the text, a TextOptions saying where it goes, and a color. Text is shaped with OpenType, so kerning, ligatures, right-to-left and complex scripts come out right. The program below captions NASA’s “Blue Marble” photograph (public domain) in Noto Sans.

Terminal

dotnet new console -o DrawText && cd DrawText
dotnet add package RecursiveAI.OneImage.Text --version 1.10.4
curl -L -o photo.jpg \
  https://images-assets.nasa.gov/image/as17-148-22727/as17-148-22727~orig.jpg
fonts=https://github.com/notofonts/notofonts.github.io/raw/main/fonts
curl -L -o NotoSans-Regular.ttf $fonts/NotoSans/hinted/ttf/NotoSans-Regular.ttf

OneImage needs the .NET 10 SDK. Put this in Program.cs and run dotnet run:

using OneImage;
using OneImage.Drawing;
using OneImage.Text;
using Path = OneImage.Drawing.Path;
 
Image photo = Image.Load("photo.jpg").Resize(width: 1200);
 
Font font = new FontCollection().Add("NotoSans-Regular.ttf").CreateFont(44);
var options = new TextOptions(font)
{
    // The origin is the bottom center of the text block, 40 px above the edge.
    Origin = new(photo.Width / 2, photo.Height - 40),
    HorizontalAlignment = HorizontalAlignment.Center,
    VerticalAlignment = VerticalAlignment.Bottom,
    TextAlignment = TextAlignment.Center,
    WrappingLength = 1000,   // wrap lines wider than 1000 px
};
string caption = "The Blue Marble, photographed from Apollo 17 on its way to the Moon";
 
// Measure the text to put a translucent box behind it.
var box = TextMeasurer.MeasureBounds(caption, options);
Console.WriteLine($"{TextMeasurer.CountLines(caption, options)} lines, "
                + $"{box.Width:0}x{box.Height:0} px");
 
Path back = Path.RoundedRectangle(box.X - 24, box.Y - 16,
                                  box.Width + 48, box.Height + 32, radius: 12);
photo.Fill(new Rgba32(0, 0, 0, 160), back)
     .DrawText(caption, options, new Rgba32(255, 255, 255, 255))
     .Save("captioned.jpg");
Console.WriteLine("Saved captioned.jpg");

Text

2 lines, 972x88 px
Saved captioned.jpg

Origin is in pixels from the top-left corner, and the two alignments say which point of the text block it is, so you don’t have to measure text to center or right-align it. WrappingLength breaks lines at word boundaries.

Outlined text

To keep text readable over both light and dark areas without a box, draw it with a Brush for the fill and a Pen for the outline:

using OneImage;
using OneImage.Drawing;
using OneImage.Text;
 
Image photo = Image.Load("photo.jpg").Resize(width: 1200);
Font font = new FontCollection().Add("NotoSans-Regular.ttf").CreateFont(36);
 
var options = new TextOptions(font)
{
    Origin = new(photo.Width - 30, photo.Height - 30),
    HorizontalAlignment = HorizontalAlignment.Right,
    VerticalAlignment = VerticalAlignment.Bottom,
};
photo.DrawText("Photo: NASA", options,
               Brush.Solid(new Rgba32(255, 255, 255, 220)),
               new Pen(Brush.Solid(new Rgba32(0, 0, 0, 160)), width: 2))
     .Save("credited.jpg");
Console.WriteLine("Saved credited.jpg");

Text

Saved credited.jpg

Limits

No fonts are bundled. Installed fonts are available through SystemFonts, but containers usually have none; a TrueType, OpenType, WOFF or WOFF2 file you ship gives the same output everywhere.
Sizes are in pixels. Scale the font size from the image width if your images vary in size.
Emoji and missing characters need a font that has them; add one with FallbackFontFamilies.

For a translucent mark across the whole image, see Add a watermark. Rich text, vertical layout and hinting are in the Text docs.