C# 生成缩略图文件大小

Question

我有以下代码来拍摄图像并生成缩略图。

如何更改质量或压缩以通过编程获得更小的文件？

Image thumbNail = image.GetThumbnailImage(Width, Height, null, new IntPtr());

Answer 1

如果您确实需要更好地控制生成的缩略图，最好通过手动生成更小尺寸和不同质量的图像来制作自己的缩略图。 GetThumbnailImage 不会给您太多控制权。

请参阅这篇文章了解它是如何完成的。 http://www.switchonthecode.com/tutorials/csharp-tutorial-image-editing-saving-cropping-and-resizing

Answer 2

使用Image.Save 保存thumbNail 时，您可以通过传递EncoderParameter 来指定质量。请参阅：Reducing JPEG Picture Quality using C#

EncoderParameter epQuality = new EncoderParameter(
    System.Drawing.Imaging.Encoder.Quality,
    (int)numQual.Value);

...
newImage.Save(..., iciJpegCodec, epParameters);

Answer 3

您不使用 GetThumbnailImage API：

protected Stream ResizeImage(string source, int width, int height) {
            using (System.Drawing.Bitmap bmp = (System.Drawing.Bitmap)System.Drawing.Bitmap.FromFile(source))
            using (System.Drawing.Bitmap newBmp = new System.Drawing.Bitmap(width, height)) 
            using (System.Drawing.Graphics graphic = System.Drawing.Graphics.FromImage(newBmp))
            {

                graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                graphic.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
                graphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

                graphic.DrawImage(bmp, 0, 0, width, height);

                MemoryStream ms = new MemoryStream();
                newBmp.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
                return ms;

            }             
        }