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[MrAksel]

I know many wonder how those good image editors save images with f.ex 50% quality.
A normal image (in vb) can be saved to a stream or a file. Here is the possible ways to save to a file:

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Image.Save(filename As String)
Image.Save(filename As String, ImageFormat)
Image.Save(filename As String, imageCodec as ImageCodecInfo, encoderParams As EncoderParameters)

You will be learning about the last one.
Remember to import the System.Drawing.Imaging namespace

So lets say we have an image called someimage, we want to save this image with 75% quality. We need to get the right image codec, and we need to create the encoder parameters. We could create a method to get the right codec. It would be like this:

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    Function GetImageCodec(ByVal mimeType As String) As ImageCodecInfo
        'Stores the avaliable codec infos in an array
        Dim codecs() As ImageCodecInfo = ImageCodecInfo.GetImageEncoders
        Dim theRightOne As ImageCodecInfo
        For codecIndex = 0 To codecs.Length - 1
            'Check if it is the right codec
            If codecs(codecIndex).MimeType = mimeType Then
                'This matches the codec we want
                theRightOne = codecs(codecIndex)
                Exit For
            End If
        Next

        'Cleanup
        Array.Clear(codecs, 0, codecs.Length)
        Return theRightOne
    End Function

The mimetype for JPEG is image/jpeg.
We also need to create the encoder parameters. That can be done easy.

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        Dim EncoderParameters As New EncoderParameters(1) 'Store 1 parameter
        EncoderParameters.Param(0) = New EncoderParameter(Encoder.Quality, 75) 'Creates an EncoderParameter with the Quality encoder and sets it value to 75 (%)

Remember that the mimeType for the JPEG codec is image/jpeg. Now we can save our image with this little piece of code:

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    Function SaveImageWithQuality(ByVal image As Image, ByVal filename As String, ByVal Quality As Integer)
        If Quality < 0 OrElse Quality > 100 Then
            Throw New ArgumentOutOfRangeException("The quality must be between 0 and 100")
            Exit Function
        End If

        Dim EncoderParameters As New EncoderParameters(1) 'Store 1 parameter
        EncoderParameters.Param(0) = New EncoderParameter(Encoder.Quality, Quality) 'Creates an EncoderParameter with the Quality encoder and sets it value from the 'Quality' parameter

        Dim codec As ImageCodecInfo = GetImageCodec("image/jpeg")

        image.Save(filename, codec, EncoderParameters) 'Saves the image to 'filename' with the jpeg encoder and the quality from the 'quality' parameter
    End Function

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SaveImageWithQuality(someimage, "Test.jpg", 50)

[comathi]

Awesome tut +rep

[MrAksel]

thx though i dont think you can +rep me since you already have

[XTechVB]

Nice tutorial dude! +rep

[Napster1488]

Good work,
i never tought it can be done in this Way.