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如何：縮放期間使用插補法模式控制影像品質

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物件的插補模式 Graphics 會影響 GDI+ 縮放（縮放和縮小）影像的方式。 列舉 InterpolationMode 會定義數種插補模式，其中一些會在下列清單中顯示：

若要延展影像，原始影像中的每個圖元都必須對應至較大影像中的圖元群組。 若要壓縮影像，原始影像中的圖元群組必須對應至較小的影像中的單一圖元。 執行這些對應之演算法的有效性會決定縮放影像的品質。 產生高品質縮放影像的演算法往往需要更多的處理時間。 在上述清單中， NearestNeighbor 是最低品質模式，而且 HighQualityBicubic 是最高品質模式。

若要設定插補模式，請將 列舉的 InterpolationMode 其中一個成員指派給 InterpolationMode 物件的 屬性 Graphics 。

範例

下列範例會繪製影像，然後使用三種不同的插補模式壓縮影像。

下圖顯示原始影像和三個較小的影像。

Screenshot that shows an image with varied interpolation settings.

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);

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)

編譯程式碼

上述範例是為了搭配 Windows Form 使用而設計，且其需要 PaintEventArgse，這是 Paint 事件處理常式的參數。

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