C#图片缩放出伪影，如何实现类似Photoshop的高质量缩放？

我尝试了各类图片缩小代码，均出现伪影问题，但手动使用Photoshop处理时无此情况，求更多修复方案。另外注意到Photoshop导出位图时可选择「progressive」模式，想知道C#中是否有类似功能？

效果对比 #

• Photoshop缩放效果（1080p→480p）：
  
• 代码缩放效果（1080p→480p）：
  

图片其他区域情况类似，衣领处的伪影是代码问题的典型示例。

当前使用的ResizeImage函数代码 #

public static Bitmap ResizeImage(Image image, int width, int height)
{
        var destRect = new System.Drawing.Rectangle(0, 0, width, height);
        var destImage = new System.Drawing.Bitmap(width, height);

        destImage.SetResolution(image.HorizontalResolution, image.VerticalResolution);

        using (var graphics = System.Drawing.Graphics.FromImage(destImage))
        {
            graphics.CompositingMode = CompositingMode.SourceCopy;
            graphics.CompositingQuality = CompositingQuality.HighQuality;
            graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
            graphics.SmoothingMode = SmoothingMode.HighQuality;
            graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

            using (var wrapMode = new System.Drawing.Imaging.ImageAttributes())
            {
                wrapMode.SetWrapMode(WrapMode.TileFlipXY);
                graphics.DrawImage(image, destRect, 0, 0, image.Width, image.Height, System.Drawing.GraphicsUnit.Pixel, wrapMode);
            }
        }

        return destImage;
}

原始图片参考 #

修复方案及相关解答 #

1. 调整插值模式与预处理 #

你当前用的HighQualityBicubic并非所有场景都最优，可以尝试切换为InterpolationMode.HighQualityBilinear，部分边缘场景下表现更柔和；另外缩放前给原图加轻微高斯模糊，能减少高频噪点带来的锯齿：

// 缩放前给原图做轻度模糊
private static Image ApplyLightBlur(Image image)
{
    Bitmap blurred = new Bitmap(image.Width, image.Height);
    using (Graphics g = Graphics.FromImage(blurred))
    {
        // 5x5均值模糊矩阵，弱化细节噪点
        float[][] blurMatrix = new float[5][];
        float weight = 1f / 25f;
        for (int i = 0; i < 5; i++)
        {
            blurMatrix[i] = new float[] { weight, weight, weight, weight, weight };
        }
        using (var attributes = new System.Drawing.Imaging.ImageAttributes())
        {
            attributes.SetColorMatrix(new System.Drawing.Imaging.ColorMatrix(blurMatrix));
            g.DrawImage(image, new Rectangle(0, 0, image.Width, image.Height), 
                        0, 0, image.Width, image.Height, GraphicsUnit.Pixel, attributes);
        }
    }
    return blurred;
}

调用时先对原图做模糊，再传入ResizeImage函数即可。

2. 改用专业图像处理库 #

System.Drawing的原生缩放算法精度有限，推荐用ImageSharp或Magick.NET这类专业库，它们的插值算法更接近Photoshop的效果：

• ImageSharp示例（用Lanczos3插值，缩小图像时细节保留+抗锯齿表现更优）：

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Processing;

public static Image ResizeWithImageSharp(Image image, int width, int height)
{
    return image.Clone(ctx => ctx.Resize(width, height, KnownResamplers.Lanczos3));
}

3. 关于Progressive模式的说明 #

Photoshop的「progressive」是JPEG的编码方式，和缩放质量无关，仅影响图片加载时的显示顺序（从模糊到清晰渐进加载）。C#中保存JPEG时可以开启这个选项：

// 保存图片时启用Progressive模式
destImage.Save("output.jpg", GetProgressiveJpegEncoder());

private static System.Drawing.Imaging.ImageCodecInfo GetProgressiveJpegEncoder()
{
    foreach (var codec in System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders())
    {
        if (codec.FormatID == System.Drawing.Imaging.ImageFormat.Jpeg.Guid)
        {
            var encoderParams = new System.Drawing.Imaging.EncoderParameters(1);
            encoderParams.Param[0] = new System.Drawing.Imaging.EncoderParameter(
                System.Drawing.Imaging.Encoder.SaveFlag, 
                (long)System.Drawing.Imaging.EncoderValue.Progressive
            );
            return codec;
        }
    }
    return null;
}

内容的提问来源于stack exchange，提问作者Sparks