操作說明:設定 JPEG 壓縮層級
當您將影像儲存至磁碟以減少檔案大小或改善其品質時,可能會想要修改影像的參數。 您可以修改其壓縮層級來調整 JPEG 影像的品質。 若要在儲存 JPEG 映射時指定壓縮層級,您必須建立 EncoderParameters 物件,並將它傳遞至 Save 類別的 Image 方法。 EncoderParameters初始化 物件,使其具有包含一個 EncoderParameter 的陣列。 當您建立 EncoderParameter 時,請指定 Quality 編碼器和所需的壓縮層級。
範例
下列範例程式碼會建立 物件,並儲存三個 EncoderParameter JPEG 影像。 每個 JPEG 映射都會以不同的品質層級儲存,方法是修改 long
傳遞至 EncoderParameter 建構函式的值。 品質層級 0 對應到最大壓縮,而品質層級 100 對應到最小壓縮。
private void VaryQualityLevel()
{
// Get a bitmap. The using statement ensures objects
// are automatically disposed from memory after use.
using (Bitmap bmp1 = new Bitmap(@"C:\TestPhoto.jpg"))
{
ImageCodecInfo jpgEncoder = GetEncoder(ImageFormat.Jpeg);
// Create an Encoder object based on the GUID
// for the Quality parameter category.
System.Drawing.Imaging.Encoder myEncoder =
System.Drawing.Imaging.Encoder.Quality;
// Create an EncoderParameters object.
// An EncoderParameters object has an array of EncoderParameter
// objects. In this case, there is only one
// EncoderParameter object in the array.
EncoderParameters myEncoderParameters = new EncoderParameters(1);
EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, 50L);
myEncoderParameters.Param[0] = myEncoderParameter;
bmp1.Save(@"c:\TestPhotoQualityFifty.jpg", jpgEncoder, myEncoderParameters);
myEncoderParameter = new EncoderParameter(myEncoder, 100L);
myEncoderParameters.Param[0] = myEncoderParameter;
bmp1.Save(@"C:\TestPhotoQualityHundred.jpg", jpgEncoder, myEncoderParameters);
// Save the bitmap as a JPG file with zero quality level compression.
myEncoderParameter = new EncoderParameter(myEncoder, 0L);
myEncoderParameters.Param[0] = myEncoderParameter;
bmp1.Save(@"C:\TestPhotoQualityZero.jpg", jpgEncoder, myEncoderParameters);
}
}
Private Sub VaryQualityLevel()
' Get a bitmap. The Using statement ensures objects
' are automatically disposed from memory after use.
Using bmp1 As New Bitmap("C:\TestPhoto.jpg")
Dim jpgEncoder As ImageCodecInfo = GetEncoder(ImageFormat.Jpeg)
' Create an Encoder object based on the GUID
' for the Quality parameter category.
Dim myEncoder As System.Drawing.Imaging.Encoder = System.Drawing.Imaging.Encoder.Quality
' Create an EncoderParameters object.
' An EncoderParameters object has an array of EncoderParameter
' objects. In this case, there is only one
' EncoderParameter object in the array.
Dim myEncoderParameters As New EncoderParameters(1)
Dim myEncoderParameter As New EncoderParameter(myEncoder, 50L)
myEncoderParameters.Param(0) = myEncoderParameter
bmp1.Save("c:\TestPhotoQualityFifty.jpg", jpgEncoder, myEncoderParameters)
myEncoderParameter = New EncoderParameter(myEncoder, 100L)
myEncoderParameters.Param(0) = myEncoderParameter
bmp1.Save("C:\TestPhotoQualityHundred.jpg", jpgEncoder, myEncoderParameters)
' Save the bitmap as a JPG file with zero quality level compression.
myEncoderParameter = New EncoderParameter(myEncoder, 0L)
myEncoderParameters.Param(0) = myEncoderParameter
bmp1.Save("C:\TestPhotoQualityZero.jpg", jpgEncoder, myEncoderParameters)
End Using
End Sub
private ImageCodecInfo GetEncoder(ImageFormat format)
{
ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();
foreach (ImageCodecInfo codec in codecs)
{
if (codec.FormatID == format.Guid)
{
return codec;
}
}
return null;
}
Private Function GetEncoder(ByVal format As ImageFormat) As ImageCodecInfo
Dim codecs As ImageCodecInfo() = ImageCodecInfo.GetImageEncoders()
Dim codec As ImageCodecInfo
For Each codec In codecs
If codec.FormatID = format.Guid Then
Return codec
End If
Next codec
Return Nothing
End Function
編譯程式碼
這個範例需要:
Windows Forms 應用程式。
, PaintEventArgs 這是 的參數 PaintEventHandler 。
名為
TestPhoto.jpg
且位於 c:\的 映射檔。