Resizing Images

Resizing an image is probably the most common processing operation that applications use. ImageSharp offers an incredibly flexible collection of resize options that allow developers to choose sizing algorithms, sampling algorithms, and gamma handling as well as other options.

The Basics

Resizing an image involves the process of creating and iterating through the pixels of a target image and sampling areas of a source image to choose what color to implement for each pixel. The sampling algorithm chosen affects the target color and can dramatically alter the result. Different samplers are usually chosen based upon the use case - For example NearestNeigbor is often used for fast, low quality thumbnail generation, Lanczos3 for high quality thumbnails due to it's sharpening effect, and Spline for high quality enlargement due to it's smoothing effect.

With ImageSharp we default to Bicubic as it is a very robust algorithm offering good quality output when both reducing and enlarging images but you can easily set the algorithm when processing.

A full list of out-of-the-box sampling algorithms can be found here:

Resize the given image using the default Bicubic sampler.

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Processing;

using (Image image = Image.Load(inStream))
{
    int width = image.Width / 2;
    int height = image.Height / 2;
    image.Mutate(x => x.Resize(width, height));

    image.Save(outPath);
}

Resize the given image using the Lanczos3 sampler:

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Processing;
using SixLabors.ImageSharp.Formats.Png; //used only for the PNG encoder below

using (Image image = Image.Load(inStream))
{
    int width = image.Width / 2;
    int height = image.Height / 2;
    image.Mutate(x => x.Resize(width, height, KnownResamplers.Lanczos3));

    image.Save(outStream, new PngEncoder());//Replace Png encoder with the file format of choice
}

Note

If you pass 0 as any of the values for width and height dimensions then ImageSharp will automatically determine the correct opposite dimensions size to preserve the original aspect ratio.

Advanced Resizing

In addition to basic resizing operations ImageSharp also offers more advanced features. Check out the ResizeOptions class for details.