c#工具类之Bitmap缩放帮忙类

using System.Drawing;
using System.Drawing.Drawing2D;

/// <summary>
/// BitmapHelper
/// </summary>
public static class BitmapScaleHelper
{
/// <summary>
/// 缩放图片
/// </summary>
/// <param name="bitmap">原图片</param>
/// <param name="width">新图片宽度</param>
/// <param name="height">新图片高度</param>
/// <returns>新图片</returns>
public static Bitmap ScaleToSize(this Bitmap bitmap, int width, int height)
{
if (bitmap.Width == width && bitmap.Height == height)
{
return bitmap;
}

var scaledBitmap = new Bitmap(width, height);
using (var g = Graphics.FromImage(scaledBitmap))
{
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
g.DrawImage(bitmap, 0, 0, width, height);
}

return scaledBitmap;
}

/// <summary>
/// 缩放图片
/// </summary>
/// <param name="bitmap">原图片</param>
/// <param name="size">新图片大小</param>
/// <returns>新图片</returns>
public static Bitmap ScaleToSize(this Bitmap bitmap, Size size)
{
return bitmap.ScaleToSize(size.Width, size.Height);
}

/// <summary>
/// 按比例来缩放
/// </summary>
/// <param name="bitmap">原图</param>
/// <param name="ratio">ratio大于1,则放大;否则缩小</param>
/// <returns>新图片</returns>
public static Bitmap ScaleToSize(this Bitmap bitmap, float ratio)
{
return bitmap.ScaleToSize((int)(bitmap.Width * ratio), (int)(bitmap.Height * ratio));
}

/// <summary>
/// 按给定长度/宽度等比例缩放
/// </summary>
/// <param name="bitmap">原图</param>
/// <param name="width">新图片宽度</param>
/// <param name="height">新图片高度</param>
/// <returns>新图片</returns>
public static Bitmap ScaleProportional(this Bitmap bitmap, int width, int height)
{
float proportionalWidth, proportionalHeight;

if (width.Equals(0))
{
proportionalWidth = ((float)height) / bitmap.Size.Height * bitmap.Width;
proportionalHeight = height;
}
else if (height.Equals(0))
{
proportionalWidth = width;
proportionalHeight = ((float)width) / bitmap.Size.Width * bitmap.Height;
}
else if (((float)width) / bitmap.Size.Width * bitmap.Size.Height <= height)
{
proportionalWidth = width;
proportionalHeight = ((float)width) / bitmap.Size.Width * bitmap.Height;
}
else
{
proportionalWidth = ((float)height) / bitmap.Size.Height * bitmap.Width;
proportionalHeight = height;
}

return bitmap.ScaleToSize((int)proportionalWidth, (int)proportionalHeight);
}

/// <summary>
/// 按给定长度/宽度缩放,同时可以设置背景色
/// </summary>
/// <param name="bitmap">原图</param>
/// <param name="backgroundColor">背景色</param>
/// <param name="width">新图片宽度</param>
/// <param name="height">新图片高度</param>
/// <returns></returns>
public static Bitmap ScaleToSize(this Bitmap bitmap, Color backgroundColor, int width, int height)
{
var scaledBitmap = new Bitmap(width, height);
using (var g = Graphics.FromImage(scaledBitmap))
{
g.Clear(backgroundColor);

var proportionalBitmap = bitmap.ScaleProportional(width, height);

var imagePosition = new Point((int)((width - proportionalBitmap.Width) / 2m), (int)((height - proportionalBitmap.Height) / 2m));
g.DrawImage(proportionalBitmap, imagePosition);
}

return scaledBitmap;
}
}