C# WinForms Bitmap保存图片画质极差，如何优化？

方案1：直接保存PictureBox中的原始图像 #

通过DrawToBitmap从控件渲染图像会引入画质损失，因为它捕获的是控件的显示状态（可能经过缩放、低质量插值处理）。直接使用PictureBox的Image属性保存原始图像数据，是最可靠的保画质方式：

// 保存为无损PNG格式
pageImage.Image.Save(originalLocation, System.Drawing.Imaging.ImageFormat.Png);

// 若需保存为JPEG并设置最高画质
var qualityParams = new System.Drawing.Imaging.EncoderParameters(1);
qualityParams.Param[0] = new System.Drawing.Imaging.EncoderParameter(
    System.Drawing.Imaging.Encoder.Quality, 100L);
var jpegCodec = ImageCodecInfo.GetImageEncoders()
    .First(codec => codec.FormatID == System.Drawing.Imaging.ImageFormat.Jpeg.Guid);
pageImage.Image.Save(originalLocation, jpegCodec, qualityParams);

方案2：优化DrawToBitmap的渲染参数 #

如果必须从控件渲染（比如控件上叠加了自定义绘制内容），需要在绘制时配置高质量渲染选项，减少画质损耗：

using (Bitmap bmp = new Bitmap(pageImage.Width, pageImage.Height))
{
    using (Graphics g = Graphics.FromImage(bmp))
    {
        // 开启高质量渲染模式
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
        g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
        
        pageImage.DrawToBitmap(bmp, new Rectangle(0, 0, pageImage.Width, pageImage.Height));
    }
    // 优先选择无损格式保存
    bmp.Save(originalLocation, System.Drawing.Imaging.ImageFormat.Png);
}

方案3：修正PictureBox的缩放模式 #

如果PictureBox的SizeMode设置为StretchImage、Zoom等缩放模式，控件会自动缩放图像导致画质下降。可以临时切换为原始尺寸模式后再渲染：

var originalSizeMode = pageImage.SizeMode;
pageImage.SizeMode = PictureBoxSizeMode.Normal;

using (Bitmap bmp = new Bitmap(pageImage.Width, pageImage.Height))
{
    pageImage.DrawToBitmap(bmp, new Rectangle(0, 0, pageImage.Width, pageImage.Height));
    bmp.Save(originalLocation, System.Drawing.Imaging.ImageFormat.Png);
}

pageImage.SizeMode = originalSizeMode;

内容的提问来源于stack exchange，提问作者Silme94