JPG Processing in .NET

[Samuel]

I shrink pictures in .NET and the quality of the JPG is very low.

Is there anything to do about that?

Thank you,
Samuel

 

[Herfried K. Wagner [MVP]]

Am 04.03.2010 01:35, schrieb Samuel:

I shrink pictures in .NET and the quality of the JPG is very low.

Is there anything to do about that?

..NET's JPEG encoder is not as good as the encoder included in Photoshop,
but you can still adjust the quality:

EncoderParameter Class (System.Drawing.Imaging)
<URL:http://msdn.microsoft.com/en-us/library/system.drawing.imaging.encoderparameter.aspx>

 

[Andrew Morton]

I shrink pictures in .NET and the quality of the JPG is very low.

Is there anything to do about that?

A couple of points:

1) Use a pixel format with an alpha channel when resizing, or else you may
get grey lines at the image borders:

Dim bmp2 As New Bitmap(CInt(targetW), CInt(targetH),
PixelFormat.Format32bppArgb)
Dim g As Graphics = Graphics.FromImage(bmp2)
' some experimentation may be needed with the InterpolationMode
g.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic


2) Use the Image.Save(String, ImageCodecInfo, EncoderParameters) overload,
which allows you to set the "quality" used when saving a jfif; to get the
last two parameters:

Dim jpegEncoder As ImageCodecInfo = GetEncoder(ImageFormat.Jpeg)
Dim myEncoderParameters As New EncoderParameters(1)
myEncoderParameters.Param(0) = New
EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 85L)


''' <summary>
''' Return an ImageEncoder given an ImageFormat.
''' </summary>
''' <param name="format">An ImageFormat.</param>
''' <returns>An ImageEncoder.</returns>
''' <remarks></remarks>
Private Function GetEncoder(ByVal format As ImageFormat) As ImageCodecInfo
For Each codec As ImageCodecInfo In ImageCodecInfo.GetImageEncoders()
If codec.FormatID = format.Guid Then
Return codec
End If
Next codec
Return Nothing
End Function


HTH,

Andrew

 

[Samuel]

Significant improvement.

Thank you

A couple of points:

1) Use a pixel format with an alpha channel when resizing, or else you may
get grey lines at the image borders:

Dim bmp2 As New Bitmap(CInt(targetW), CInt(targetH),
PixelFormat.Format32bppArgb)
Dim g As Graphics = Graphics.FromImage(bmp2)
' some experimentation may be needed with the InterpolationMode
g.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic


2) Use the Image.Save(String, ImageCodecInfo, EncoderParameters) overload,
which allows you to set the "quality" used when saving a jfif; to get the
last two parameters:

Dim jpegEncoder As ImageCodecInfo = GetEncoder(ImageFormat.Jpeg)
Dim myEncoderParameters As New EncoderParameters(1)
myEncoderParameters.Param(0) = New
EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 85L)


''' <summary>
''' Return an ImageEncoder given an ImageFormat.
''' </summary>
''' <param name="format">An ImageFormat.</param>
''' <returns>An ImageEncoder.</returns>
''' <remarks></remarks>
Private Function GetEncoder(ByVal format As ImageFormat) As ImageCodecInfo
For Each codec As ImageCodecInfo In ImageCodecInfo.GetImageEncoders()
If codec.FormatID = format.Guid Then
Return codec
End If
Next codec
Return Nothing
End Function


HTH,

Andrew