VB.NET resize and crop images - vb.net

Question

i have a VSTO for powerpoint and want to resize images so they are the same size as the slide. a sample image i have is 1000x300 and the slide is 960x540. so this is the code i have:
_W=960
_H=540
Dim img As Image = System.Drawing.Bitmap.FromFile(file1)
OldRect = New RectangleF(233, 0, 533, 300) ' calculated values to crop left and right
NewRect = New RectangleF(0, 0, _W, _H)
Dim bmp As Bitmap = New Bitmap(img, _W, _H)
Dim g As Graphics = Graphics.FromImage(bmp)
g.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic
g.PixelOffsetMode = Drawing2D.PixelOffsetMode.HighQuality
g.CompositingQuality = Drawing2D.CompositingQuality.HighQuality
g.DrawImage(img, NewRect, OldRect, GraphicsUnit.Pixel)
img.Save(file2, Imaging.ImageFormat.Png)
but when i look at file2 it's the same 1000x300 file as the original. what am i missing here?

Answer 1

#plutonix; you're spot on. i was under the wrong impression that DrawImage would replace the image it was offered. but saving the bitmap the graphics object was created with produced the intended image.
bmp.Save(file2, Imaging.ImageFormat.Png)
works perfect. thanks!

Answer 2

The answer posted here is good but there is one major problem of quality that need to be addressed. In most cased you have to Crop Image and Maintain the Quality so in that regard, I have improved the crop feature of a sample and posted below is the link. This demo is in VB.NET but you can easily understand the concept and make adjustments.
http://www.mediafire.com/file/70rmlpcdjyxo8gc/ImageCroppingDemo_-_Maintain_Image_Quality.zip/file
CODES For Cropping (VB.NET)
Dim cropX As Integer
Dim cropY As Integer
Dim cropWidth As Integer
Dim cropHeight As Integer
Dim oCropX As Integer
Dim oCropY As Integer
Dim cropBitmap As Bitmap
Dim Loadedimage As Image
Public cropPen As Pen
Public cropPenSize As Integer = 1 '2
Public cropDashStyle As Drawing2D.DashStyle = Drawing2D.DashStyle.Solid
Public cropPenColor As Color = Color.Yellow
Private Sub crobPictureBox_MouseDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles crobPictureBox.MouseDown
Try
If e.Button = Windows.Forms.MouseButtons.Left Then
cropX = e.X
cropY = e.Y
cropPen = New Pen(cropPenColor, cropPenSize)
cropPen.DashStyle = DashStyle.DashDotDot
Cursor = Cursors.Cross
End If
crobPictureBox.Refresh()
Catch exc As Exception
End Try
End Sub
Dim tmppoint As Point
Private Sub crobPictureBox_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles crobPictureBox.MouseMove
Try
If crobPictureBox.Image Is Nothing Then Exit Sub
If e.Button = Windows.Forms.MouseButtons.Left Then
crobPictureBox.Refresh()
cropWidth = e.X - cropX
cropHeight = e.Y - cropY
crobPictureBox.CreateGraphics.DrawRectangle(cropPen, cropX, cropY, cropWidth, cropHeight)
End If
' GC.Collect()
Catch exc As Exception
If Err.Number = 5 Then Exit Sub
End Try
End Sub
Private Sub crobPictureBox_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles crobPictureBox.MouseUp
Try
Cursor = Cursors.Default
Try
If cropWidth < 1 Then
Exit Sub
End If
Dim smallWidthPercentage As Single = (cropWidth / crobPictureBox.Width) * 100
Dim smallHeightPercentage As Single = (cropHeight / crobPictureBox.Height) * 100
Dim smallXPercentage As Single = (cropX / crobPictureBox.Width) * 100
Dim smallYPercentage As Single = (cropY / crobPictureBox.Height) * 100
smallHeightPercentage += 10
smallYPercentage -= 10
Dim Widthdifference As Integer = Loadedimage.Width - crobPictureBox.Width
Dim HeightDifference As Integer = Loadedimage.Height - crobPictureBox.Height
Dim rect As Rectangle
rect = New Rectangle((smallXPercentage / 100) * Loadedimage.Width, (smallYPercentage / 100) * Loadedimage.Height, (smallWidthPercentage / 100) * Loadedimage.Width, (smallHeightPercentage / 100) * Loadedimage.Height)
Dim bit As Bitmap = New Bitmap(Loadedimage, Loadedimage.Width, Loadedimage.Height)
cropBitmap = New Bitmap(Loadedimage, (smallWidthPercentage / 100) * Loadedimage.Width, (smallHeightPercentage / 100) * Loadedimage.Height)
Dim g As Graphics = Graphics.FromImage(cropBitmap)
g.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic
g.PixelOffsetMode = Drawing2D.PixelOffsetMode.HighQuality
g.CompositingQuality = Drawing2D.CompositingQuality.HighQuality
g.DrawImage(bit, 0, 0, rect, GraphicsUnit.Pixel)
PreviewPictureBox.Image = cropBitmap
Catch exc As Exception
End Try
Catch exc As Exception
End Try
End Sub