Resize an Image Properly?

[Redth]

It's me again...

I've spent a few hours today trying to figure out how to properly resize a jpg image programmatically...

hellswraith has helped me out a bunch already, giving me a very nice example to start off with... but i've found that using GDI+ (at least in the way i'm using it) doesn't properly.. my resized image looks to be very low quality, even when i try saving it with the jpg quality at 100...

here's the sub i'm using to resize the image:

Function ResizeImage(ByVal MaxWidth As Integer, ByVal MaxHeight As Integer, ByVal Image As Bitmap) As Bitmap
 
        Dim ScaleFactor As Decimal
        Dim NewSize As SizeF
 
        If CInt(Image.Size.Width) > MaxWidth Or CInt(Image.Size.Height) > MaxHeight Then
 
            If CInt(Image.Size.Width) > CInt(Image.Size.Height) Then
                'Image Width is too big
                ScaleFactor = CDec(MaxWidth / CInt(Image.Size.Width))
 
            Else
                'Image Height is too big
                ScaleFactor = CDec(MaxHeight / CInt(Image.Size.Height))
            End If
 
            NewSize.Width = Image.Size.Width * ScaleFactor
            NewSize.Height = Image.Size.Height * ScaleFactor
 
            'Return the resized image
            ResizeImage = Image.GetThumbnailImage(NewSize.Width, NewSize.Height, Nothing, Nothing)
 
        End If
    End Function

Now, here's the original image i'm starting with:



Here's the image that my code resizes: (Keep in mind, the way i saved this image, i used jpeg encoder at a quality of 100)



And Finally, here's what Photoshop ends up with when it resizes my image to the same size as my code:



So, as you can see, my code doesn't do the job... So, i'm still looking for a proper way to do this, be it through a 3rd party .NET library, or code... i would PREFER to have code to do this in .NET myself, but if nothing else, i guess 3rd party would have to suffice... thanks for the help guys!

[PT Exorcist]

well welcome to the club, u are not alone, a LOT of ppl asked already how to make that and couldnt figure it out, maybe the best thing u(we) can do is do it via api

anyways if u find a way plz share it with us (even if it's via api)

[hellswraith]

Try saving it as a bitmap, see if the quality is there. If it is, it means the jpg encoding is messing up somewhere.

[Redth]

i tried saving it as an Imaging.ImageFormat.bmp

however, i get a General GDI+ error when i do that... it only lets me save it as a jpeg... :/ maybe because the input file is a jpeg?

[Redth]

can anyone offer other solutions? I really think this issue is largely unaddressed, and it would be great to have this information readily available to others who are looking for it as well....

[hellswraith]

Check this link out:
http://www.dotnet247.com/247reference/msgs/1/7407.aspx

http://www.codeguru.com/bitmap/index.shtml

[Redth]

those links were good hellswraith

i've now come up with a function for resizing images PROPERLY.... it takes a Drawing.Image, and max width and max height... it then resizes it to constrain to the max width and max height, keeping the image in proportion to the original... it returns a bitmap, which in turn can be saved as jpeg, or whatever... but remember if you're saving as jpeg, you can have control over the quality setting as well...

Function ResizeImage(ByVal MaxWidth As Integer, ByVal MaxHeight As Integer, ByVal Image As Drawing.Image) As Bitmap
 
        Dim ScaleFactor As Decimal
        Dim NewSize As SizeF
 
        If CInt(Image.Size.Width) > MaxWidth Or CInt(Image.Size.Height) > MaxHeight Then
 
            If CInt(Image.Size.Width) > CInt(Image.Size.Height) Then
                'Image Width is too big
                ScaleFactor = CDec(MaxWidth / CInt(Image.Size.Width))
 
            Else
                'Image Height is too big
                ScaleFactor = CDec(MaxHeight / CInt(Image.Size.Height))
            End If
 
            'Calculate the New height and width
            NewSize.Width = Image.Size.Width * ScaleFactor
            NewSize.Height = Image.Size.Height * ScaleFactor
 
            'Rotate the image.  Apparently this gives it better quality somehow
            Image.RotateFlip(RotateFlipType.Rotate180FlipNone)
            Image.RotateFlip(RotateFlipType.Rotate180FlipNone)
 
            'The returned image is a new bitmap based on the one given, but with new dimensions
            ResizeImage = New Bitmap(Image, NewSize.Width, NewSize.Height)
 
        End If
    End Function

this gives a GOOD result.. so, it is possible to do this with just the GDI, and quite simple too. .i just think a LOT of people are misinformed about how this exactly works... so hopefully this will help everyone out...

[hellswraith]

That is cool you got it working right. The code I started you off with was for me to create thumbnails with, so the quality wasn't an issue. I am glad you got this, now I can use it to for some other things.

I am still suspicious of this part though:

            
            'Rotate the image.  Apparently this gives it better quality somehow
            Image.RotateFlip(RotateFlipType.Rotate180FlipNone)
            Image.RotateFlip(RotateFlipType.Rotate180FlipNone)

Seems a little wierd that doing that would cause a better quality.

Could you also post how you save to jpg with setting the quality?

[Redth]

here's what i'm using to save with adjustable image quality...

' Get an array of ImageEncoders..array item 1 is Jpeg.
Dim imgCodecs() As Drawing.Imaging.ImageCodecInfo = Imaging.ImageCodecInfo.GetImageEncoders()
 
' Set quality Parameter for the Jpeg codec
Dim imgParams As Imaging.EncoderParameters = New Imaging.EncoderParameters(1)
Dim imgQuality As Imaging.EncoderParameter = New Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100)
 
' Set quality
imgParams.Param(0) = imgQuality
 
'Here's how you save with jpeg settings
myImage.Save("C:\MyImage.jpg", imgCodecs(1), imgParams)

[Redth]

remember, the 100 number is the quality...

so that can be adjusted from 0 to 100 .... 100 being the best quality...

[MrPolite]

Originally posted by hellswraith
Could you also post how you save to jpg with setting the quality?

http://www.vbforums.com/showthread.p...hlight=quality

edit: eeh sounds like someone already answered you

[PT Exorcist]

Originally posted by hellswraith
That is cool you got it working right. The code I started you off with was for me to create thumbnails with, so the quality wasn't an issue. I am glad you got this, now I can use it to for some other things.

I am still suspicious of this part though:

            
            'Rotate the image.  Apparently this gives it better quality somehow
            Image.RotateFlip(RotateFlipType.Rotate180FlipNone)
            Image.RotateFlip(RotateFlipType.Rotate180FlipNone)

Seems a little wierd that doing that would cause a better quality.

Could you also post how you save to jpg with setting the quality?

when doing web pages thumbnails on the fly with this method doesnt it take a LOT compared to getthumbnailsize?