How to resize an Image C#

in this question, you'll have some answers, including mine:

public Image resizeImage(int newWidth, int newHeight, string stPhotoPath)
 {
     Image imgPhoto = Image.FromFile(stPhotoPath); 

     int sourceWidth = imgPhoto.Width;
     int sourceHeight = imgPhoto.Height;

     //Consider vertical pics
    if (sourceWidth < sourceHeight)
    {
        int buff = newWidth;

        newWidth = newHeight;
        newHeight = buff;
    }

    int sourceX = 0, sourceY = 0, destX = 0, destY = 0;
    float nPercent = 0, nPercentW = 0, nPercentH = 0;

    nPercentW = ((float)newWidth / (float)sourceWidth);
    nPercentH = ((float)newHeight / (float)sourceHeight);
    if (nPercentH < nPercentW)
    {
        nPercent = nPercentH;
        destX = System.Convert.ToInt16((newWidth -
                  (sourceWidth * nPercent)) / 2);
    }
    else
    {
        nPercent = nPercentW;
        destY = System.Convert.ToInt16((newHeight -
                  (sourceHeight * nPercent)) / 2);
    }

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


    Bitmap bmPhoto = new Bitmap(newWidth, newHeight,
                  PixelFormat.Format24bppRgb);

    bmPhoto.SetResolution(imgPhoto.HorizontalResolution,
                 imgPhoto.VerticalResolution);

    Graphics grPhoto = Graphics.FromImage(bmPhoto);
    grPhoto.Clear(Color.Black);
    grPhoto.InterpolationMode =
        System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;

    grPhoto.DrawImage(imgPhoto,
        new Rectangle(destX, destY, destWidth, destHeight),
        new Rectangle(sourceX, sourceY, sourceWidth, sourceHeight),
        GraphicsUnit.Pixel);

    grPhoto.Dispose();
    imgPhoto.Dispose();
    return bmPhoto;
}

You could try net-vips, the C# binding for libvips. It's a lazy, streaming, demand-driven image processing library, so it can do operations like this without needing to load the whole image.

For example, it comes with a handy image thumbnailer:

using Image image = Image.Thumbnail("image.jpg", 300, 300);
image.WriteToFile("my-thumbnail.jpg");

It also supports smart crop, a way of intelligently determining the most important part of the image and keeping it in focus while cropping the image. For example:

using Image image = Image.Thumbnail("owl.jpg", 128, crop: Enums.Interesting.Attention);
image.WriteToFile("tn_owl.jpg");

Where owl.jpg is an off-centre composition:

Gives this result:

First it shrinks the image to get the vertical axis to 128 pixels, then crops down to 128 pixels across using the attention strategy. This one searches the image for features which might catch a human eye, see Smartcrop() for details.

Use below function with below example for changing image size :

//Example : 
System.Net.Mime.MediaTypeNames.Image newImage = System.Net.Mime.MediaTypeNames.Image.FromFile("SampImag.jpg");
System.Net.Mime.MediaTypeNames.Image temImag = FormatImage(newImage, 100, 100);

//image size modification unction   
public static System.Net.Mime.MediaTypeNames.Image FormatImage(System.Net.Mime.MediaTypeNames.Image img, int outputWidth, int outputHeight)
{

    Bitmap outputImage = null;
    Graphics graphics = null;
    try
    {
         outputImage = new Bitmap(outputWidth, outputHeight, System.Drawing.Imaging.PixelFormat.Format16bppRgb555);
         graphics = Graphics.FromImage(outputImage);
         graphics.DrawImage(img, new Rectangle(0, 0, outputWidth, outputHeight),
         new Rectangle(0, 0, img.Width, img.Height), GraphicsUnit.Pixel);

         return outputImage;
     }
     catch (Exception ex)
     {
           return img;
     }
}

Below function will return the new size to display the image.This may not be helpful here.But it will return resized Display Rectangle size.

 public static  class ResizeImage
{
    /// <summary>
    /// Return new resized size to display the image
    /// </summary>
    /// <param name="srcrectanle">source rectangle of image or you can pass the bitmap and set the size accrodingly</param>
    /// <param name="initSize">initial size of the page to draw image</param>
    /// <returns></returns>
    public static SizeF getResizedRectangle(RectangleF srcrectanle, SizeF initSize)
    {
        float sw = srcrectanle.Width;
        float sh = srcrectanle.Height;
        float dw = initSize.Width;
        float dh = initSize.Height;
        float finalHeight, finalWidth;
        float Sourceratio = sw / sh;

        if (Sourceratio >= 1)
        {
            finalWidth = (int)dw;
            float ratio = sw / dw;
            finalHeight = (sh / ratio);
        }
        else
        {
            finalHeight = (int)dh;
            float ratio = sh / dh;
            finalWidth = (sw / ratio);
        }
        return new SizeF(finalHeight, finalHeight);


    }
}