How to: Encode and Decode a JPEG Image

 

The following examples show how to decode and encode a JPEG image using the specific JpegBitmapDecoder and JpegBitmapEncoder objects.

Example

This example demonstrates how to decode a JPEG image using a JpegBitmapDecoder from a FileStream.

' Open a Stream and decode a JPEG image
Dim imageStreamSource As New FileStream("tulipfarm.jpg", FileMode.Open, FileAccess.Read, FileShare.Read)
Dim decoder As New JpegBitmapDecoder(imageStreamSource, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default)
Dim bitmapSource As BitmapSource = decoder.Frames(0)

' Draw the Image
Dim myImage As New Image()
myImage.Source = bitmapSource
myImage.Stretch = Stretch.None
myImage.Margin = New Thickness(20)

Example

This example demonstrates how to encode a BitmapSource into a JPEG image using a JpegBitmapEncoder.

Dim width As Integer = 128
Dim height As Integer = width
Dim stride As Integer = CType(width / 8, Integer)
Dim pixels(height * stride) As Byte

' Define the image palette
Dim myPalette As BitmapPalette = BitmapPalettes.Halftone256

' Creates a new empty image with the pre-defined palette
Dim image As BitmapSource = System.Windows.Media.Imaging.BitmapSource.Create(width, height, 96, 96, PixelFormats.Indexed1, myPalette, pixels, stride)
Dim stream As New FileStream("new.jpg", FileMode.Create)
Dim encoder As New JpegBitmapEncoder()
Dim myTextBlock As New TextBlock()
myTextBlock.Text = "Codec Author is: " + encoder.CodecInfo.Author.ToString()
encoder.FlipHorizontal = True
encoder.FlipVertical = False
encoder.QualityLevel = 30
encoder.Rotation = Rotation.Rotate90
encoder.Frames.Add(BitmapFrame.Create(image))
encoder.Save(stream)

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