我正在尝试使用MVC3的WebImage助手创建缩略图。
原始图像是带有透明背景的.png。当我尝试使用以下内容调整大小时:
var image = blob.DownloadByteArray();
new WebImage(image)
.Resize(50, 50)
.Write();
生成的缩略图将原始透明背景替换为黑色背景。
答案 0 :(得分:6)
上面这个答案很棒,但我做了一些微调并实现了图像的“保持比例”,这样我们就不会得到拉伸的图像了。
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Web.Helpers;
public static class ResizePng
{
private static IDictionary<string, ImageFormat> _transparencyFormats = new Dictionary<string, ImageFormat>(StringComparer.OrdinalIgnoreCase) { { "png", ImageFormat.Png }, { "gif", ImageFormat.Gif } };
public static WebImage ResizePreserveTransparency(this WebImage image, int width, int height)
{
ImageFormat format = null;
if (!_transparencyFormats.TryGetValue(image.ImageFormat, out format))
{
return image.Resize(width, height);
}
//keep ratio *************************************
double ratio = (double)image.Width / image.Height;
double desiredRatio = (double)width / height;
if (ratio > desiredRatio)
{
height = Convert.ToInt32(width / ratio);
}
if (ratio < desiredRatio)
{
width = Convert.ToInt32(height * ratio);
}
//************************************************
using (Image resizedImage = new Bitmap(width, height))
{
using (Bitmap source = new Bitmap(new MemoryStream(image.GetBytes())))
{
using (Graphics g = Graphics.FromImage(resizedImage))
{
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
g.DrawImage(source, 0, 0, width, height);
}
}
using (MemoryStream ms = new MemoryStream())
{
resizedImage.Save(ms, format);
return new WebImage(ms.ToArray());
}
}
}
}
答案 1 :(得分:2)
您应该为gif和png图像编写自己的resize方法。我已经为Web Image创建了扩展图像的扩展。请参阅下面的方法代码:
public static class WebImageExtension
{
private static readonly IDictionary<string, ImageFormat> TransparencyFormats =
new Dictionary<string, ImageFormat>(StringComparer.OrdinalIgnoreCase)
{{"png", ImageFormat.Png}, {"gif", ImageFormat.Gif}};
public static WebImage Resize(this WebImage image, int width)
{
double aspectRatio = (double)image.Width / image.Height;
var height = Convert.ToInt32(width/aspectRatio);
ImageFormat format;
if (!TransparencyFormats.TryGetValue(image.ImageFormat.ToLower(), out format))
{
return image.Resize(width, height);
}
using (Image resizedImage = new Bitmap(width, height))
{
using (var source = new Bitmap(new MemoryStream(image.GetBytes())))
{
using (Graphics g = Graphics.FromImage(resizedImage))
{
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
g.DrawImage(source, 0, 0, width, height);
}
}
using (var ms = new MemoryStream())
{
resizedImage.Save(ms, format);
return new WebImage(ms.ToArray());
}
}
}
}
答案 2 :(得分:1)
您应该更改.Write
以传递预期的输出类型。它使用此传递类型来确定要使用的图像类型。
var image = blob.DownloadByteArray();
new WebImage(image)
.Resize(50, 50)
.Write("png");