当你使用 GDI + 绘制图像时，我认为它的缩放效果非常好。您可以使用它来创建缩放图像。

如果你想用 GDI + 缩放你的图像，你可以这样做:

Bitmap original = ...
Bitmap scaled = new Bitmap(new Size(original.Width * 4, original.Height * 4));
using (Graphics graphics = Graphics.FromImage(scaled)) {
graphics.DrawImage(original, new Rectangle(0, 0, scaled.Width, scaled.Height));
}

像 想象力和 GD这样经过测试的库可用于.NET

你也可以读读双三次插值，写写自己的东西。

尝试使用 Graphics 的不同值。插值模式。在 GDI + 中有几种典型的缩放算法。如果其中之一足以满足您的需要，您可以采用这种方法，而不必依赖外部库。

有一个关于使用 GDI + for. NET 来调整照片大小的双三次插值。

在另一个博客上也有一篇关于这个话题的文章(我想是微软员工) ，但是我在任何地方都找不到这个链接。: (也许别人可以找到它？

讨论和共享 缩放图片:源代码的 CodeProject 文章

• 使用 过滤器进行两次传递缩放
• 基于 .NET GDI + 的 C # 图像矩阵变换
• 用 用于.NET 的 GDI + 调整摄影图像的大小
• 基于 Haar 变形术的快速二进制图像缩放

您可以尝试 照片，我公司的产品之一，其中包括一个 重新取样的物体图像，有 18种过滤器类型的各种水平的质量。

典型用法是:

// BiCubic is one technique available in PhotoShop
ResampleCommand resampler = new ResampleCommand(newSize, ResampleMethod.BiCubic);
AtalaImage newImage = resampler.Apply(oldImage).Image;

此外，dotImage 还包括140个奇怪的图像处理命令，其中包括许多类似于 PhotoShop 中的过滤器，如果您正在寻找这些命令的话。

这里有一个注释很好的图像操作帮助器类，您可以查看和使用它。我将它作为一个例子来说明如何在 C # 中执行某些图像处理任务。您将对采用 System 的 ResizeImage函数感兴趣。画画。图像、宽度和高度作为参数。

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;


namespace DoctaJonez.Drawing.Imaging
{
/// <summary>
/// Provides various image untilities, such as high quality resizing and the ability to save a JPEG.
/// </summary>
public static class ImageUtilities
{
/// <summary>
/// A quick lookup for getting image encoders
/// </summary>
private static Dictionary<string, ImageCodecInfo> encoders = null;


/// <summary>
/// A lock to prevent concurrency issues loading the encoders.
/// </summary>
private static object encodersLock = new object();


/// <summary>
/// A quick lookup for getting image encoders
/// </summary>
public static Dictionary<string, ImageCodecInfo> Encoders
{
//get accessor that creates the dictionary on demand
get
{
//if the quick lookup isn't initialised, initialise it
if (encoders == null)
{
//protect against concurrency issues
lock (encodersLock)
{
//check again, we might not have been the first person to acquire the lock (see the double checked lock pattern)
if (encoders == null)
{
encoders = new Dictionary<string, ImageCodecInfo>();


//get all the codecs
foreach (ImageCodecInfo codec in ImageCodecInfo.GetImageEncoders())
{
//add each codec to the quick lookup
encoders.Add(codec.MimeType.ToLower(), codec);
}
}
}
}


//return the lookup
return encoders;
}
}


/// <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 System.Drawing.Bitmap ResizeImage(System.Drawing.Image image, int width, int height)
{
//a holder for the result
Bitmap result = new Bitmap(width, height);
//set the resolutions the same to avoid cropping due to resolution differences
result.SetResolution(image.HorizontalResolution, image.VerticalResolution);


//use a graphics object to draw the resized image into the bitmap
using (Graphics graphics = Graphics.FromImage(result))
{
//set the resize quality modes to high quality
graphics.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
//draw the image into the target bitmap
graphics.DrawImage(image, 0, 0, result.Width, result.Height);
}


//return the resulting bitmap
return result;
}


/// <summary>
/// Saves an image as a jpeg image, with the given quality
/// </summary>
/// <param name="path">Path to which the image would be saved.</param>
/// <param name="quality">An integer from 0 to 100, with 100 being the
/// highest quality</param>
/// <exception cref="ArgumentOutOfRangeException">
/// An invalid value was entered for image quality.
/// </exception>
public static void SaveJpeg(string path, Image image, int quality)
{
//ensure the quality is within the correct range
if ((quality < 0) || (quality > 100))
{
//create the error message
string error = string.Format("Jpeg image quality must be between 0 and 100, with 100 being the highest quality.  A value of {0} was specified.", quality);
//throw a helpful exception
throw new ArgumentOutOfRangeException(error);
}


//create an encoder parameter for the image quality
EncoderParameter qualityParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
//get the jpeg codec
ImageCodecInfo jpegCodec = GetEncoderInfo("image/jpeg");


//create a collection of all parameters that we will pass to the encoder
EncoderParameters encoderParams = new EncoderParameters(1);
//set the quality parameter for the codec
encoderParams.Param[0] = qualityParam;
//save the image using the codec and the parameters
image.Save(path, jpegCodec, encoderParams);
}


/// <summary>
/// Returns the image codec with the given mime type
/// </summary>
public static ImageCodecInfo GetEncoderInfo(string mimeType)
{
//do a case insensitive search for the mime type
string lookupKey = mimeType.ToLower();


//the codec to return, default to null
ImageCodecInfo foundCodec = null;


//if we have the encoder, get it to return
if (Encoders.ContainsKey(lookupKey))
{
//pull the codec from the lookup
foundCodec = Encoders[lookupKey];
}


return foundCodec;
}
}
}

更新

一些人已经在评论中询问了如何使用 ImageUtitility 类的示例，所以现在就可以开始了。

//resize the image to the specified height and width
using (var resized = ImageUtilities.ResizeImage(image, 50, 100))
{
//save the resized image as a jpeg with a quality of 90
ImageUtilities.SaveJpeg(@"C:\myimage.jpeg", resized, 90);
}

注意

请记住，图像是一次性的，因此您需要将调整大小的结果分配给 using 声明(或者您可以使用 try finally，并确保在 finally 中调用 pose)。

这是我在 Paint.NET 的图像重采样代码: 各种简单的图像处理技术中发现的一篇文章，作者是 Paul Bourke。

如果是 Lowres CGI 你可以试试这个 二维图像滤波器

这个可能会有帮助

    public Image ResizeImage(Image source, RectangleF destinationBounds)
{
RectangleF sourceBounds = new RectangleF(0.0f,0.0f,(float)source.Width, (float)source.Height);
RectangleF scaleBounds = new RectangleF();


Image destinationImage = new Bitmap((int)destinationBounds.Width, (int)destinationBounds.Height);
Graphics graph = Graphics.FromImage(destinationImage);
graph.InterpolationMode =
System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;


// Fill with background color
graph.FillRectangle(new SolidBrush(System.Drawing.Color.White), destinationBounds);


float resizeRatio, sourceRatio;
float scaleWidth, scaleHeight;


sourceRatio = (float)source.Width / (float)source.Height;


if (sourceRatio >= 1.0f)
{
//landscape
resizeRatio = destinationBounds.Width / sourceBounds.Width;
scaleWidth = destinationBounds.Width;
scaleHeight = sourceBounds.Height * resizeRatio;
float trimValue = destinationBounds.Height - scaleHeight;
graph.DrawImage(source, 0, (trimValue / 2), destinationBounds.Width, scaleHeight);
}
else
{
//portrait
resizeRatio = destinationBounds.Height/sourceBounds.Height;
scaleWidth = sourceBounds.Width * resizeRatio;
scaleHeight = destinationBounds.Height;
float trimValue = destinationBounds.Width - scaleWidth;
graph.DrawImage(source, (trimValue / 2), 0, scaleWidth, destinationBounds.Height);
}


return destinationImage;


}

请注意，InterpolationMode.HighQualityBicubic-> 这通常是性能和结果之间的一个很好的折衷。

使用这个库: http://imageresizing.net

读读这篇由图书馆作者撰写的文章: 使用.NET 的20个图像大小缺陷

你可以试试 魔法核心。与双三次重采样相比，在向上缩放时产生的像素化伪影较少，而且在向下缩放时也能得到很好的效果。 源代码可以在网站的 c # 中找到。

试试这个基本的代码片段:

private static Bitmap ResizeBitmap(Bitmap srcbmp, int width, int height )
{
Bitmap newimage = new Bitmap(width, height);
using (Graphics g = Graphics.FromImage(newimage))
g.DrawImage(srcbmp, 0, 0, width, height);
return newimage;
}

我对琼斯博士的回答有些改进。

它适用于谁想要如何比例调整图像大小。它测试和我的工作。

第一类的方法是:

public static System.Drawing.Bitmap ResizeImage(System.Drawing.Image image, Size size)
{
return ResizeImage(image, size.Width, size.Height);
}




public static Size GetProportionedSize(Image image, int maxWidth, int maxHeight, bool withProportion)
{
if (withProportion)
{
double sourceWidth = image.Width;
double sourceHeight = image.Height;


if (sourceWidth < maxWidth && sourceHeight < maxHeight)
{
maxWidth = (int)sourceWidth;
maxHeight = (int)sourceHeight;
}
else
{
double aspect = sourceHeight / sourceWidth;


if (sourceWidth < sourceHeight)
{
maxWidth = Convert.ToInt32(Math.Round((maxHeight / aspect), 0));
}
else
{
maxHeight = Convert.ToInt32(Math.Round((maxWidth * aspect), 0));
}
}
}


return new Size(maxWidth, maxHeight);
}

以及根据这些代码提供的新用途:

using (var resized = ImageUtilities.ResizeImage(image, ImageUtilities.GetProportionedSize(image, 50, 100)))
{
ImageUtilities.SaveJpeg(@"C:\myimage.jpeg", resized, 90);
}