Question

After searching, I’ve discovered this code:

Public Sub ResizeImage(ByVal scaleFactor As Double, ByVal fromStream As Stream, ByVal toStream As Stream)
    Dim image__1 = System.Drawing.Image.FromStream(fromStream)
    Dim newWidth = CInt(image__1.Width * scaleFactor)
    Dim newHeight = CInt(image__1.Height * scaleFactor)
    Dim thumbnailBitmap = New System.Drawing.Bitmap(newWidth, newHeight)

    Dim thumbnailGraph = System.Drawing.Graphics.FromImage(thumbnailBitmap)
    thumbnailGraph.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality
    thumbnailGraph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality
    thumbnailGraph.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic

    Dim imageRectangle = New System.Drawing.Rectangle(0, 0, newWidth, newHeight)
    thumbnailGraph.DrawImage(image__1, imageRectangle)
    thumbnailBitmap.Save(toStream, image__1.RawFormat)

    thumbnailGraph.Dispose()
    thumbnailBitmap.Dispose()
    image__1.Dispose()
End Sub

There are 2 things I can’t “modify” to solve my problem:

1. I wouldn’t like to pass a stream, but I prefer to pass a path like C:\mysite\photo\myphoto.gif. How can I “convert” it to accept a file and not a stream?
2. In this function I’ve to pass a “scale” value. But I prefer to check if the image is too big (for example > 1024x768) than resize it to a max of 1024x768. How can I check this with System.Drawing.

As you can see I don’t know anything about System.Drawing so I need an “hard” help to solve this job.

Answer 1

Here is some c# code I did about 5 years ago to do this (it should still work I hope as the app hasn’t been touched since). I think it does everthing you need but it doesn’t upscale the image to 1024×768 if it is smaller. This code will only make sure that if it is larger than 1024×768, it will resize proportionally to fit within those dimensions:

const int maxWidth = 1024;
const int maxHeight = 768;
Image newImage = Image.FromFile("YourPicture.jpg");
double percentToShrink = -1;
if (newImage.Width >= newImage.Height)
{
    // Do we need to resize based on width?
    if (newImage.Width > maxWidth)
    {
        percentToShrink = (double)maxWidth / (double)newImage.Width;
    }
}
else
{
    // Do we need to resize based on width?
    if (newImage.Height > maxHeight )
    {
        percentToShrink = (double)maxHeight  / (double)newImage.Height;
    }
}

int newWidth = newImage.Width;
int newHeight = newImage.Height;

// So do we need to resize?
if (percentToShrink != -1)
{
    newWidth = (int)(newImage.Width * percentToShrink);
    newHeight = (int)(newImage.Height * percentToShrink);
}

// convert the image to a png and get a byte[]
MemoryStream imgStream = new MemoryStream();
Bitmap bmp = new Bitmap(newWidth, newHeight);
using (Graphics g = Graphics.FromImage(bmp))
{
    g.InterpolationMode =   System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
    g.FillRectangle(System.Drawing.Brushes.White, 0, 0, newWidth, newHeight);
    g.DrawImage(newImage, 0, 0, newWidth, newHeight);
}

// This can be whatever format you need
bmp.Save(imgStream, System.Drawing.Imaging.ImageFormat.Png);
byte[] imgBinaryData = imgStream.ToArray();
imgStream.Dispose();

If you need to convert this to VB.NET, you can use the C# to VB.NET converter here.