如何:缩放时使用插值模式控制图像质量

Graphics 对象的插值模式会影响 GDI+ 缩放(拉伸和收缩)图像的方式。 InterpolationMode 枚举定义了几种插值模式,其中一些模式显示在下面的列表中:

若要拉伸图像,原始图像中的每个像素都必须映射为较大图像中的一组像素。 若要收缩图像,必须将原始图像中成组的像素映射为较小图像中单个的像素。 执行这些映射的算法的效果决定缩放后图像的质量。 生成优质缩放图像的算法往往需要更长的处理时间。 在上面的列表中,NearestNeighbor 是质量最差的模式,HighQualityBicubic 是质量最好的模式。

若要设置插值模式,请将 InterpolationMode 枚举的一个成员分配给 Graphics 对象的 InterpolationMode 属性。

示例

下面的示例绘制一个图像,然后用三种不同的插值模式收缩图像。

下面的插图显示原始图像和三个较小的图像。

具有各种内插设置的图像

        Dim image As New Bitmap("GrapeBunch.bmp")
        Dim width As Integer = image.Width
        Dim height As Integer = image.Height

        ' Draw the image with no shrinking or stretching. Pass in the destination
        ' rectangle (2nd argument), the upper-left corner (3rd and 4th arguments),
        ' width (5th argument),  and height (6th argument) of the source 
        ' rectangle.
        e.Graphics.DrawImage( _
            image, _
            New Rectangle(10, 10, width, height), _
            0, _
            0, _
            width, _
            height, _
            GraphicsUnit.Pixel, _
            Nothing)

        ' Shrink the image using low-quality interpolation. 
        e.Graphics.InterpolationMode = InterpolationMode.NearestNeighbor

        ' Pass in the destination rectangle, and the upper-left corner, width, 
        ' and height of the source rectangle as above.
        e.Graphics.DrawImage( _
        image, _
        New Rectangle(10, 250, CInt(0.6 * width), CInt(0.6 * height)), _
        0, _
        0, _
        width, _
        height, _
        GraphicsUnit.Pixel)

        ' Shrink the image using medium-quality interpolation.
        e.Graphics.InterpolationMode = InterpolationMode.HighQualityBilinear

        ' Pass in the destination rectangle, and the upper-left corner, width, 
        ' and height of the source rectangle as above.
        e.Graphics.DrawImage( _
        image, _
        New Rectangle(150, 250, CInt(0.6 * width), _
        CInt(0.6 * height)), _
        0, _
        0, _
        width, _
        height, _
        GraphicsUnit.Pixel)

        ' Shrink the image using high-quality interpolation.
        e.Graphics.InterpolationMode = InterpolationMode.HighQualityBicubic

        ' Pass in the destination rectangle, and the upper-left corner, width, 
        ' and height of the source rectangle as above.
        e.Graphics.DrawImage( _
            image, _
            New Rectangle(290, 250, CInt(0.6 * width), CInt(0.6 * height)), _
            0, _
            0, _
            width, _
            height, _
            GraphicsUnit.Pixel)

Image image = new Bitmap("GrapeBunch.bmp");
int width = image.Width;
int height = image.Height;

// Draw the image with no shrinking or stretching.
e.Graphics.DrawImage(
    image,
    new Rectangle(10, 10, width, height),  // destination rectangle  
    0,
    0,           // upper-left corner of source rectangle
    width,       // width of source rectangle
    height,      // height of source rectangle
    GraphicsUnit.Pixel,
    null);

// Shrink the image using low-quality interpolation. 
e.Graphics.InterpolationMode = InterpolationMode.NearestNeighbor;
e.Graphics.DrawImage(
   image,
    new Rectangle(10, 250, (int)(0.6 * width), (int)(0.6 * height)),
    // destination rectangle 
    0,
    0,           // upper-left corner of source rectangle
    width,       // width of source rectangle
    height,      // height of source rectangle
    GraphicsUnit.Pixel);

// Shrink the image using medium-quality interpolation.
e.Graphics.InterpolationMode = InterpolationMode.HighQualityBilinear;
e.Graphics.DrawImage(
    image,
    new Rectangle(150, 250, (int)(0.6 * width), (int)(0.6 * height)),
    // destination rectangle 
    0,
    0,           // upper-left corner of source rectangle
    width,       // width of source rectangle
    height,      // height of source rectangle
    GraphicsUnit.Pixel);

// Shrink the image using high-quality interpolation.
e.Graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
e.Graphics.DrawImage(
    image,
    new Rectangle(290, 250, (int)(0.6 * width), (int)(0.6 * height)),
    // destination rectangle 
    0,
    0,           // upper-left corner of source rectangle
    width,       // width of source rectangle
    height,      // height of source rectangle
    GraphicsUnit.Pixel);

编译代码

前面的示例是为使用 Windows 窗体而设计的,它需要 Paint 事件处理程序的参数 PaintEventArgs e。

请参见

其他资源

图像、位图和图元文件

使用图像、位图、图标和图元文件