I'm trying to resize / enlarge a image achieving same good results as IrfanView program. I just took this veteran and professional program as a point of reference for comparing the resulting quality that I can achieve using my "own" image resizing algorithm within .NET.
However, my resized image is blurry in comparison, and the image size differs within the canvas size, like 1px smaller, I don't know why, I mean I don't know if this difference is a fault of mine, or a fault of IrfanView.
Original image:
Image Resized using IrfanView:
Image resized using the .NET code below:
Maybe the differences will not be noticeable at all unless you save both images to disk, and open them with any image viewer (like IrfanVieew) to pass fast between both images, so you will notice something like this:
This is the code I'm using:
Public Function Resize(source As Image, size As Size,
preserveAspectRatio As Boolean) As Drawing.Image
If (size.Width <= 0) Then
Throw New ArgumentException("Width bigger than zero is reqired.", NameOf(size))
ElseIf (size.Height <= 0) Then
Throw New ArgumentException("Height bigger than zero is reqired.", NameOf(size))
Else
Dim bmp As Drawing.Bitmap
If (preserveAspectRatio) Then
' https://codereview.stackexchange.com/a/70916/25995
Dim scaleHeight As Single = CSng(size.Height) / CSng(source.Height)
Dim scaleWidth As Single = CSng(size.Width) / CSng(source.Width)
Dim smallerScale As Single = Math.Min(scaleHeight, scaleWidth)
bmp = New Bitmap(CInt(Math.Truncate(source.Width * smallerScale)),
CInt(Math.Truncate(source.Height * smallerScale)),
source.PixelFormat)
Else
bmp = New Bitmap(size.Width, size.Height, source.PixelFormat)
End If
Using g As Graphics = Graphics.FromImage(bmp),
attributes As New ImageAttributes()
' g.CompositingQuality = CompositingQuality.AssumeLinear
g.InterpolationMode = InterpolationMode.Bicubic
g.PixelOffsetMode = PixelOffsetMode.Half
g.SmoothingMode = SmoothingMode.None
g.CompositingMode = CompositingMode.SourceCopy
' Avoid 1px semi-transparent black borders:
' https://stackoverflow.com/a/41718683/1248295
attributes.SetWrapMode(WrapMode.TileFlipX)
g.DrawImage(source, New Rectangle(Point.Empty, bmp.Size), 0, 0,
source.Width, source.Height, GraphicsUnit.Pixel, attributes)
End Using
Return bmp
End If
End Function
Why I'm getting worse results than IrfanView?. Why my image is blurry and have different size drawn within the canvas size?. What I'm doing wrong and how do I fix it?.
Please note that in the code above I tested almost all possible quality combinations. And bicubic interpolation gives me a better / sharp image than highqualitybicubic, I'm not sure if this will apply always when enlarging a image.
