高质量图像缩放库
我想用C＃调整图像的质量，与Photoshop一样好。 有没有任何C＃图像处理库可以做这件事情？
这里有一个很好的评论的图像操作助手类，你可以看看和使用。 我将它作为如何在C＃中执行某些图像处理任务的示例进行了编写。 你会对ResizeImage函数感兴趣，它将System.Drawing.Image，width和height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
有几个人在评论中询问了如何使用ImageUtilities类的样本，所以在这里。
//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一个使用声明（或者您可以最后使用一次尝试，并确保您在最后调用dispose）。
当我使用GDI +绘制图像时，在我看来它的缩放比例非常好。 您可以使用它来创建缩放图像。
如果你想用GDI +来扩展你的图像，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Imagemagick和GD的测试库可用于.NET
你也可以阅读诸如双三次插值之类的东西并编写你自己的。
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