Resize JPEG image to fixed width, while keeping aspect ratio as it is

Question

How would you resize a JPEG image, to a fixed width whilst keeping aspect ratio? In a simple way, whilst preserving quality.

Answer 1

This will scale in the vertical axis only:

    public static Image ResizeImageFixedWidth(Image imgToResize, int width)
    {
        int sourceWidth = imgToResize.Width;
        int sourceHeight = imgToResize.Height;

        float nPercent = ((float)width / (float)sourceWidth);

        int destWidth = (int)(sourceWidth * nPercent);
        int destHeight = (int)(sourceHeight * nPercent);

        Bitmap b = new Bitmap(destWidth, destHeight);
        Graphics g = Graphics.FromImage((Image)b);
        g.InterpolationMode = InterpolationMode.HighQualityBicubic;

        g.DrawImage(imgToResize, 0, 0, destWidth, destHeight);
        g.Dispose();

        return (Image)b;
    }

Answer 2

If you are reducing the width by 25 percent to a fixed value, you must reduce the height by 25 percent.

If you are increasing the width by 25 percent to a fixed value, you must increasing the height by 25 percent.

It's really straight forward.

Answer 3

Assuming there is a (double width) variable:

Image imgOriginal = Bitmap.FromFile(path);
double height = (imgOriginal.Height * width) / imgOriginal.Width;
Image imgnew = new Bitmap((int)width, (int)height, PixelFormat.Format32bppArgb);
Graphics g = Graphics.FromImage(imgnew);
g.DrawImage(imgOriginal, new Point[]{new Point(0,0), new Point(width, 0), new Point(0, height)}, new Rectangle(0,0,imgOriginal.Width, imgOriginal.Height), GraphicsUnit.Pixel);

In the end you´ll have a new image with widthxheight, then, you´ll need to flush the graphics e save the imgnew.