Image Resize in C# - Algorith to determine resize dimensions (height and width)

Question

I need to scale down an image that has a height or width greater than a predefined pixel value.

I wrote some code that takes a look at the original image, checks to

Answer 1

Fitting an image to new size requires two operations:

1. Resize - resize the source image to fit exactly one dimension (width or height - the one with the smaller ratio)

2. Crop - crop the result of the previous operation to the target dimensions

Here is a small sample:

    private static Image Resize(Image img, int width, int height)
    {
        Bitmap b = new Bitmap(width, height);
        using (Graphics g = Graphics.FromImage((Image)b))
        {
            g.DrawImage(img, 0, 0, width, height);
        }

        return (Image)b;
    }

    public static Image Crop(Image image, int width, int height)
    {
        int cropx = image.Width > width ? image.Width / 2 - width / 2 : 0;
        int cropy = image.Height > height ? image.Height / 2 - height / 2 : 0;
        width = image.Width > width ? width : image.Width;
        height = image.Height > height ? height : image.Height;

        Rectangle cropRect = new Rectangle(cropx, cropy, width, height);

        var target = new Bitmap(cropRect.Width, cropRect.Height);

        using (Graphics g = Graphics.FromImage(target))
        {
            g.DrawImage(image, new Rectangle(0, 0, target.Width, target.Height), cropRect, GraphicsUnit.Pixel);
        }

        return target;
    }

    public static Image FitToSize(Image image, int width, int height)
    {
        var wratio = 1.0 * image.Width / width;
        var hratio = 1.0 * image.Height / height;

        int wresize;
        int hresize;

        if (wratio >= hratio && wratio > 1)
        {
            wresize = (int)Math.Round((double)image.Width / hratio);
            hresize = height;

            image = Resize(image, wresize, hresize);
            image = Crop(image, width, height);  
        }
        else if (hratio >= wratio && hratio > 1)
        {
            hresize = (int)Math.Round((double)image.Height / wratio);
            wresize = width;

            image = Resize(image, wresize, hresize);
            image = Crop(image, width, height);
        }
        return image;

    }