How to resize an Image C#

This will perform a high quality resize:

/// <summary>
/// Resize the image to the specified width and height.
/// </summary>
/// <param name="image">The image to resize.</param>
/// <param name="width">The width to resize to.</param>
/// <param name="height">The height to resize to.</param>
/// <returns>The resized image.</returns>
public static Bitmap ResizeImage(Image image, int width, int height)
{
    var destRect = new Rectangle(0, 0, width, height);
    var destImage = new Bitmap(width, height);

    destImage.SetResolution(image.HorizontalResolution, image.VerticalResolution);

    using (var graphics = Graphics.FromImage(destImage))
    {
        graphics.CompositingMode = CompositingMode.SourceCopy;
        graphics.CompositingQuality = CompositingQuality.HighQuality;
        graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
        graphics.SmoothingMode = SmoothingMode.HighQuality;
        graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

        using (var wrapMode = new ImageAttributes())
        {
            wrapMode.SetWrapMode(WrapMode.TileFlipXY);
            graphics.DrawImage(image, destRect, 0, 0, image.Width,image.Height, GraphicsUnit.Pixel, wrapMode);
        }
    }

    return destImage;
}

• wrapMode.SetWrapMode(WrapMode.TileFlipXY) prevents ghosting around the image borders — naïve resizing will sample transparent pixels beyond the image boundaries, but by mirroring the image we can get a better sample (this setting is very noticeable)
• destImage.SetResolution maintains DPI regardless of physical size — may increase quality when reducing image dimensions or when printing
• Compositing controls how pixels are blended with the background — might not be needed since we’re only drawing one thing.
  • graphics.CompositingMode determines whether pixels from a source image overwrite or are combined with background pixels. SourceCopy specifies that when a color is rendered, it overwrites the background color.
  • graphics.CompositingQuality determines the rendering quality level of layered images.
• graphics.InterpolationMode determines how intermediate values between two endpoints are calculated
• graphics.SmoothingMode specifies whether lines, curves, and the edges of filled areas use smoothing (also called antialiasing) — probably only works on vectors
• graphics.PixelOffsetMode affects rendering quality when drawing the new image

Maintaining aspect ratio is left as an exercise for the reader (actually, I just don’t think it’s this function’s job to do that for you).

Also, this is a good article describing some of the pitfalls with image resizing. The above function will cover most of them, but you still have to worry about saving.