根据路径获取图片

var bmp = new Bitmap(fileName);

更改图片尺寸

Image img;

var bmp = new Bitmap(width, height);
bmp.SetResolution(source.HorizontalResolution, source.VerticalResolution);
using (var g = Graphics.FromImage(bmp))
{
    g.CompositingMode = CompositingMode.SourceCopy;
    switch (quality)
    {
        case SmoothingMode.AntiAlias:
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.PixelOffsetMode = PixelOffsetMode.HighQuality;
            g.SmoothingMode = SmoothingMode.AntiAlias;
            break;...