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图形对象到图像文件

system.drawing asp.net c#

niaher · 技术社区 · 15 年前

我想裁剪和调整图像的大小。这是我的代码:

Image image = Image.FromFile(AppDomain.CurrentDomain.BaseDirectory + "Cropper/tests/castle.jpg");

// Crop and resize the image.
Rectangle destination = new Rectangle(0, 0, 200, 120);
Graphics graphic = Graphics.FromImage(image);
graphic.DrawImage(image, destination, int.Parse(X1.Value), int.Parse(Y1.Value), int.Parse(Width.Value), int.Parse(Height.Value), GraphicsUnit.Pixel);

现在,我假设生成的裁剪/调整大小的图像存储在绘图对象。问题是-如何将其保存到文件中?

3 回复 | 直到 6 年前

Fredrik Mörk 15 年前

这个 Graphics 从中获得的对象 Graphics.FromImage 是图像的绘图面。因此,您可以在完成后简单地保存图像对象。

string fileName = AppDomain.CurrentDomain.BaseDirectory + "Cropper/tests/castle.jpg");
using (Image image = Image.FromFile(fileName)
{
    using (Graphics graphic = Graphics.FromImage(image))
    {
        // Crop and resize the image.
        Rectangle destination = new Rectangle(0, 0, 200, 120);
        graphic.DrawImage(image, destination, int.Parse(X1.Value), int.Parse(Y1.Value), int.Parse(Width.Value), int.Parse(Height.Value), GraphicsUnit.Pixel);
    }
    image.Save(fileName);
}

尽管在JPG图像上重复这样做可能不是一件好事;图像每次都被重新编码,而且由于JPG使用破坏性压缩方法,每次都会丢失一些图像质量。不过,如果这是一个每图像一次的操作,我不会担心这个问题。

Guffa 15 年前

不, Graphics 对象不包含任何图像数据,它用于在画布上绘制,画布通常是屏幕或 Bitmap 对象。

因此,您需要创建一个 位图 对象的大小正确,并创建 绘图 该位图的对象。然后你可以保存它。记住对象实现 IDisposable 应释放,例如使用 using 条款:

using (Image image = Image.FromFile(AppDomain.CurrentDomain.BaseDirectory + "Cropper/tests/castle.jpg")) {

   // Create bitmap
   using (Bitmap newImage = new Bitmap(200, 120)) {

      // Crop and resize the image.
      Rectangle destination = new Rectangle(0, 0, 200, 120);
      using (Graphics graphic = Graphics.FromImage(newImage)) {
         graphic.DrawImage(image, destination, int.Parse(X1.Value), int.Parse(Y1.Value), int.Parse(Width.Value), int.Parse(Height.Value), GraphicsUnit.Pixel);
      }
      newImage.Save(AppDomain.CurrentDomain.BaseDirectory + "Cropper/tests/castle_icon.jpg", ImageFormat.Jpeg);
   }
}

Craig.Feied 6 年前

这不是OP问题的直接答案,但它是一个经常被忽视的工具,可以让您以不同的方式处理事情,如果证明有必要的话。

人们常说,不可能获取图形对象的内容。这根本不是真的。使用正确的方法,您可以使用hdc和bitblt访问画布上的数据。这里有一种方法可以使用c:

    enum TernaryRasterOperations : uint
    {
        /// <summary>dest = source</summary>
        SRCCOPY = 0x00CC0020,
        /// <summary>dest = source OR dest</summary>
        SRCPAINT = 0x00EE0086,
        /// <summary>dest = source AND dest</summary>
        SRCAND = 0x008800C6,
        /// <summary>dest = source XOR dest</summary>
        SRCINVERT = 0x00660046,
        /// <summary>dest = source AND (NOT dest)</summary>
        SRCERASE = 0x00440328,
        /// <summary>dest = (NOT source)</summary>
        NOTSRCCOPY = 0x00330008,
        /// <summary>dest = (NOT src) AND (NOT dest)</summary>
        NOTSRCERASE = 0x001100A6,
        /// <summary>dest = (source AND pattern)</summary>
        MERGECOPY = 0x00C000CA,
        /// <summary>dest = (NOT source) OR dest</summary>
        MERGEPAINT = 0x00BB0226,
        /// <summary>dest = pattern</summary>
        PATCOPY = 0x00F00021,
        /// <summary>dest = DPSnoo</summary>
        PATPAINT = 0x00FB0A09,
        /// <summary>dest = pattern XOR dest</summary>
        PATINVERT = 0x005A0049,
        /// <summary>dest = (NOT dest)</summary>
        DSTINVERT = 0x00550009,
        /// <summary>dest = BLACK</summary>
        BLACKNESS = 0x00000042,
        /// <summary>dest = WHITE</summary>
        WHITENESS = 0x00FF0062,
        /// <summary>
        /// Capture window as seen on screen.  This includes layered windows 
        /// such as WPF windows with AllowsTransparency="true"
        /// </summary>
        CAPTUREBLT = 0x40000000
    }

    [DllImport("gdi32.dll", EntryPoint = "BitBlt", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool BitBlt([In] IntPtr hdc, int nXDest, int nYDest, int nWidth, int nHeight, [In] IntPtr hdcSrc, int nXSrc, int nYSrc, TernaryRasterOperations dwRop);

    public static Bitmap CopyGraphicsContent(Graphics source, Rectangle rect)
    {
        Bitmap bmp = new Bitmap(rect.Width, rect.Height);

        using (Graphics dest = Graphics.FromImage(bmp))
        {
            IntPtr hdcSource = source.GetHdc();
            IntPtr hdcDest = dest.GetHdc();

            BitBlt(hdcDest, 0, 0, rect.Width, rect.Height, hdcSource, rect.X, rect.Y, TernaryRasterOperations.SRCCOPY);

            source.ReleaseHdc(hdcSource);
            dest.ReleaseHdc(hdcDest);
        }

        return bmp;
    }