C# 压缩图片

.net下跨平台图像处理

https://github.com/mono/SkiaSharp

安装包

skiasharp

效果

代码

ImageCompression.cs

using SkiaSharp;

namespace ImageCompressStu01
{
    /// 

    /// 图片压缩
    /// 
    public class ImageCompression
    {
        /// 

        /// 压缩图片
        /// 
        /// 原文件位置
        /// 生成目标文件位置
        /// 最大宽度，根据此宽度计算是否需要缩放，计算新高度
        /// 图片质量，范围0-100
        public static void Compress(string source, string target, decimal maxWidth, int quality)
        {
            using (var file = File.OpenRead(source))
            using (var fileStream = new SKManagedStream(file))
            using (var bitmap = SKBitmap.Decode(fileStream))
            {
                var width = (decimal)bitmap.Width;
                var height = (decimal)bitmap.Height;
                var newWidth = width;
                var newHeight = height;
                if (width > maxWidth)
                {
                    newWidth = maxWidth;
                    newHeight = height / width * maxWidth;
                }
                using (var resized = bitmap.Resize(new SKImageInfo((int)newWidth, (int)newHeight), SKFilterQuality.Medium))
                {
                    if (resized != null)
                    {
                        using (var image = SKImage.FromBitmap(resized))
                        using (var writeStream = File.OpenWrite(target))
                        {
                            image.Encode(SKEncodedImageFormat.Jpeg, quality).SaveTo(writeStream);
                        }
                    }
                }
            }
        }
    }
}

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Program.cs

namespace ImageCompressStu01
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string source = "001.jpg";
            //实验1 不改变尺寸，图片质量改为80，存为jpg图片
            ImageCompression.Compress(source, "target-1.jpg", 1920, 80);
            //实验2 不改变尺寸，图片质量改为80，存为png图片
            ImageCompression.Compress(source, "target-2.png", 1920, 80);
            //实验3 尺寸缩放到宽度800，图片质量改为80，存为jpg图片
            ImageCompression.Compress(source, "target-3.jpg", 800, 80);
            //实验4 尺寸缩放到宽度800，图片质量改为60，存为jpg图片
            ImageCompression.Compress(source, "target-4.jpg", 800, 60);
        }
    }
}
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这个是针对桌面或者控制台项目，web项目处理方式可以参考下面的方法

/// 

/// 压缩图片
/// 
/// IFormFile转化为stream
/// 最大宽度，根据此宽度计算是否需要缩放，计算新高度
/// 图片质量，范围0-100
public static byte[]? Compress(Stream file, decimal maxWidth, int quality)
{
    byte[]? result = null;
    using (var fileStream = new SKManagedStream(file))
    using (var bitmap = SKBitmap.Decode(fileStream))
    {
        var width = (decimal)bitmap.Width;
        var height = (decimal)bitmap.Height;
        var newWidth = width;
        var newHeight = height;
        if (width > maxWidth)
        {
            newWidth = maxWidth;
            newHeight = height / width * maxWidth;
        }
        using (var resized = bitmap.Resize(new SKImageInfo((int)newWidth, (int)newHeight), SKFilterQuality.Medium))
        {
            if (resized != null)
            {
                using (var image = SKImage.FromBitmap(resized))
                {
                    result = image.Encode(SKEncodedImageFormat.Jpeg, quality).ToArray();
                }
            }
        }
    }
    return result;
}
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IFormfile转stream方法如下

//内存流
var memory = new MemoryStream();
await formFile.CopyToAsync(memory);
//一定要重置一下，要不然执行压缩会报错
stream.Seek(0, SeekOrigin.Begin);
//文件流
var filePath = "xxxxx.txt";
using (var stream = System.IO.File.Create(filePath))
{
    await formFile.CopyToAsync(stream);
}
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参考1
参考2

扩展

生成海报的开源库，可以跨平台使用
https://github.com/SixLabors/ImageSharp