将所有文件转换为JPG格式的C#代码

Question

我有以下类似的函数：

    // Convert To JPG 
    // 
    public string AlltoJPG(FileInfo foo)
    {
        // Get file extension
        string fileExtension = foo.Extension;

        // Get file name without extenstion
        string fileName = foo.Name.Replace(foo.Extension, string.Empty) + ".jpg";

        /*------------------------------------------------------------------------*/

        /// <Check for PNG File Format>
        if (fileExtension == ".png" || fileExtension == ".PNG")
        {
            System.Drawing.Image img = System.Drawing.Image.FromFile(foo.FullName);

            // Assumes img is the PNG you are converting
            using (Bitmap b = new Bitmap(img.Width, img.Height))
            {
                using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(b))
                {
                    g.Clear(System.Drawing.Color.White);
                    g.DrawImageUnscaled(img, 0, 0);
                }

                // Save the image as a JPG
                b.Save(fileName, System.Drawing.Imaging.ImageFormat.Jpeg);
            }

        }

        /*------------------------------------------------------------------------*/

        /// <Check for GIF File Format>
        if (fileExtension == ".gif" || fileExtension == ".GIF")
        {
            System.Drawing.Image img = System.Drawing.Image.FromFile(foo.FullName);

            // Construct a bitmap from the image resource.
            Bitmap bmp1 = new Bitmap(img.Width, img.Height);

            // Save the image as a JPG
            bmp1.Save(fileName, System.Drawing.Imaging.ImageFormat.Jpeg);
        }

        /*------------------------------------------------------------------------*/

        /// <Check for BMP File Format>
        if (fileExtension == ".bmp" || fileExtension == ".BMP")
        {
            System.Drawing.Image img = System.Drawing.Image.FromFile(foo.FullName);

            // Construct a bitmap from the image resource.
            Bitmap bmp1 = new Bitmap(img.Width, img.Height);

            // Save the image as a JPG
            bmp1.Save(fileName, System.Drawing.Imaging.ImageFormat.Jpeg);
        }

        /*------------------------------------------------------------------------*/

        /// <Check for TIFF File Format>
        if (fileExtension == ".tiff" || fileExtension == ".TIFF")
        {
            System.Drawing.Image img = System.Drawing.Image.FromFile(foo.FullName);

            // Construct a bitmap from the image resource.
            Bitmap bmp1 = new Bitmap(img.Width, img.Height);

            // Save the image as a JPG
            bmp1.Save(fileName, System.Drawing.Imaging.ImageFormat.Jpeg);
        }

        /*------------------------------------------------------------------------*/
        fileName = foo.DirectoryName + "\\" + fileName;
        return fileName;
    }

我试图将 bmp,png,gif,tiff 文件格式转换为 jpg，但是使用 GDI+ 时会报错：

System.OutOfMemoryException was unhandled
Message=Bellek yetersiz.
Source=System.Drawing
StackTrace:
konum: System.Drawing.Image.FromFile(String filename, Boolean useEmbeddedColorManagement)
konum: System.Drawing.Image.FromFile(String filename)

那么我该如何避免这种情况并将至少 PNG 和 BMP 文件转换为 JPG 呢？

下面是出现错误的图片：

- Berker Yüceer

---

请看这里：https://dev59.com/-3NA5IYBdhLWcg3wC5Xh - Raphaël Althaus

堆栈跟踪与您提供的代码不匹配...在您的代码中没有名为 OriginalImage 的变量。 - Shai

@RaphaëlAlthaus，是的，我之前已经检查过了..照片没有问题，而是GDI+引起了这个麻烦。 - Berker Yüceer

我刚刚再次检查了一下，发现 JPG 文件没有问题，但当涉及到 PNG 时就出现了问题。因此，我怀疑这里可能是 alpha 区域的问题。 - Berker Yüceer

Answer 1

我找到了问题所在！是由PNG alpha通道引起的。

感谢max，下面的链接解决了我的问题：

如何将透明PNG加载到位图并忽略alpha通道

---

public static void SetAlpha(this Bitmap bmp, byte alpha)
{
    if(bmp == null) throw new ArgumentNullException("bmp");

    var data = bmp.LockBits(
        new Rectangle(0, 0, bmp.Width, bmp.Height),
        System.Drawing.Imaging.ImageLockMode.ReadWrite,
        System.Drawing.Imaging.PixelFormat.Format32bppArgb);

    var line = data.Scan0;
    var eof = line + data.Height * data.Stride;
    while(line != eof)
    {
        var pixelAlpha = line + 3;
        var eol = pixelAlpha + data.Width * 4;
        while(pixelAlpha != eol)
        {
            System.Runtime.InteropServices.Marshal.WriteByte(
                pixelAlpha, alpha);
            pixelAlpha += 4;
        }
        line += data.Stride;
    }
    bmp.UnlockBits(data);
}

使用方法：

var pngImage = new Bitmap("filename.png");
pngImage.SetAlpha(255);

---

设置 alpha 后，它开始正常工作。

- Berker Yüceer

Answer 2

gif、png 和 tiff 代码块缺少 using 子句，导致 GDI 引用泄漏。

- asawyer