如何：确定编码器支持的参数
更新：2007 年 11 月
可以调整图像参数，例如质量和压缩级别，但必须知道给定的图像编码器支持哪些参数。Image 类提供了 GetEncoderParameterList 方法，以便您可以确定特定编码器支持哪些图像参数。可使用 GUID 指定编码器。GetEncoderParameterList 方法返回 EncoderParameter 对象的数组。
示例
下面的示例代码输出 JPEG 编码器支持的参数。使用 Encoder 类概述中的参数类别和关联的 GUID 列表，可确定每个参数的类别。
Private Sub GetSupportedParameters(ByVal e As PaintEventArgs)
Dim bitmap1 As New Bitmap(1, 1)
Dim jpgEncoder As ImageCodecInfo = GetEncoder(ImageFormat.Jpeg)
Dim paramList As EncoderParameters = _
bitmap1.GetEncoderParameterList(jpgEncoder.Clsid)
Dim encParams As EncoderParameter() = paramList.Param
Dim paramInfo As New StringBuilder()
Dim i As Integer
For i = 0 To encParams.Length - 1
paramInfo.Append("Param " & i & " holds " & _
encParams(i).NumberOfValues & " items of type " & _
encParams(i).Type.ToString() & vbCr & vbLf & "Guid category: " & _
encParams(i).Encoder.Guid.ToString() & vbCr & vbLf)
Next i
e.Graphics.DrawString(paramInfo.ToString(), _
Me.Font, Brushes.Red, 10.0F, 10.0F)
End Sub
Private Function GetEncoder(ByVal format As ImageFormat) As ImageCodecInfo
Dim codecs As ImageCodecInfo() = ImageCodecInfo.GetImageDecoders()
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
private void GetSupportedParameters(PaintEventArgs e)
{
Bitmap bitmap1 = new Bitmap(1, 1);
ImageCodecInfo jpgEncoder = GetEncoder(ImageFormat.Jpeg);
EncoderParameters paramList = bitmap1.GetEncoderParameterList(jpgEncoder.Clsid);
EncoderParameter[] encParams = paramList.Param;
StringBuilder paramInfo = new StringBuilder();
for (int i = 0; i < encParams.Length; i++)
{
paramInfo.Append("Param " + i + " holds " + encParams[i].NumberOfValues +
" items of type " +
encParams[i].ValueType + "\r\n" + "Guid category: " + encParams[i].Encoder.Guid + "\r\n");
}
e.Graphics.DrawString(paramInfo.ToString(), this.Font, Brushes.Red, 10.0F, 10.0F);
}
private ImageCodecInfo GetEncoder(ImageFormat format)
{
ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();
foreach (ImageCodecInfo codec in codecs)
{
if (codec.FormatID == format.Guid)
{
return codec;
}
}
return null;
}
编译代码
此示例需要：
Windows 窗体应用程序。
PaintEventArgs，它是 PaintEventHandler 的一个参数。