/// <summary>
/// Allows for image resizing. if AllowLargerImageCreation = true 
/// you want to increase the size of the image
/// </summary>
/// <param name="bytes"></param>
/// <param name="NewWidth"></param>
/// <param name="MaxHeight"></param>
/// <param name="AllowLargerImageCreation"></param>
/// <returns></returns>
/// <remarks></remarks>
public static byte[] ResizeImage(byte[] bytes, int NewWidth, int MaxHeight, bool AllowLargerImageCreation)
{

	Image FullsizeImage = null;
	Image ResizedImage = null;
	//Cast bytes to an image
	FullsizeImage = byteArrayToImage(bytes);

	// Prevent using images internal thumbnail
	FullsizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone);
	FullsizeImage.RotateFlip(System.Drawing.RotateFlipType.Rotate180FlipNone);

	// If we are re sizing upwards to a bigger size
	if (AllowLargerImageCreation) {
		if (FullsizeImage.Width <= NewWidth) {
			NewWidth = FullsizeImage.Width;
		}
	}

	//Keep aspect ratio
	int NewHeight = FullsizeImage.Height * NewWidth / FullsizeImage.Width;
	if (NewHeight > MaxHeight) {
		// Resize with height instead
		NewWidth = FullsizeImage.Width * MaxHeight / FullsizeImage.Height;
		NewHeight = MaxHeight;
	}

	ResizedImage = FullsizeImage.GetThumbnailImage(NewWidth, NewHeight, null, IntPtr.Zero);

	// Clear handle to original file so that we can overwrite it if necessary
	FullsizeImage.Dispose();

	return imageToByteArray(ResizedImage);
}


/// <summary>
/// convert image to byte array
/// </summary>
/// <param name="imageIn"></param>
/// <returns></returns>
private static byte[] imageToByteArray(System.Drawing.Image imageIn)
{
	MemoryStream ms = new MemoryStream();
	imageIn.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
	return ms.ToArray();
}


/// <summary>
/// Convert a byte array to an image
/// </summary>
/// <remarks></remarks>
public static Image byteArrayToImage(byte[] byteArrayIn)
{
	MemoryStream ms = new MemoryStream(byteArrayIn);
	Image returnImage = Image.FromStream(ms);
	return returnImage;
}

Resize Images Keeping Aspect Ratio

resize, image, c

C#