C#针对System.Drawing.Bitmap压缩的实现

using System;
using System.Drawing;
using System.Drawing.Imaging;

public class ImageCompressor
{
    public static void CompressAndSave(Bitmap bitmap, string outputPath, long quality = 80L)
    {
        // 指定编码器为 JPEG
        ImageCodecInfo jpgEncoder = GetEncoder(ImageFormat.Jpeg);

        // 设置压缩质量
        Encoder qualityEncoder = Encoder.Quality;
        EncoderParameters encoderParams = new EncoderParameters(1);
        EncoderParameter qualityParam = new EncoderParameter(qualityEncoder, quality); // 0-100
        encoderParams.Param[0] = qualityParam;

        // 保存图像
        bitmap.Save(outputPath, jpgEncoder, encoderParams);
    }

    private static ImageCodecInfo GetEncoder(ImageFormat format)
    {
        ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();
        foreach (ImageCodecInfo codec in codecs)
        {
            if (codec.FormatID == format.Guid)
            {
                return codec;
            }
        }
        return null;
    }
}

Bitmap bmp = new Bitmap("input.png");
ImageCompressor.CompressAndSave(bmp, "output.jpg", 70L); // 压缩质量设为70%
bmp.Dispose();

public static Bitmap ResizeBitmap(Bitmap original, int newWidth, int newHeight)
{
    Bitmap resized = new Bitmap(newWidth, newHeight);
    using (Graphics g = Graphics.FromImage(resized))
    {
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
        g.DrawImage(original, 0, 0, newWidth, newHeight);
    }
    return resized;
}

public static byte[] CompressBitmapToBytes(Bitmap bitmap, long quality = 80L)
{
    using (var ms = new MemoryStream())
    {
        ImageCodecInfo jpgEncoder = GetEncoder(ImageFormat.Jpeg);
        Encoder qualityEncoder = Encoder.Quality;
        EncoderParameters encoderParams = new EncoderParameters(1);
        encoderParams.Param[0] = new EncoderParameter(qualityEncoder, quality);

        bitmap.Save(ms, jpgEncoder, encoderParams);
        return ms.ToArray();
    }
}

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Processing;
using SixLabors.ImageSharp.Formats.Jpeg;

var image = Image.Load("input.png");
image.Mutate(x => x.Resize(image.Width / 2, image.Height / 2)); // 缩放
image.SaveAsJpeg("output.jpg", new JpegEncoder { Quality = 70 }); // 压缩质量