Dynamically assign watermark text size based on image size c#

Question

I have a scenario where the Watermark text size should be assigned automatically as per the Image size. I am new to C# drawing features. Please help me get some workaround for this.

Current Logic to apply watermark text with fixed size on the image

protected byte[] WatermarkImage(string PhysicalPath, string Watermarktext)
{

        byte[] imageBytes = null;
        if (File.Exists(PhysicalPath))
        {
            // This is the Name which will appear as a watermark on image.
            string watermark = Watermarktext;

            Image image = Image.FromFile(PhysicalPath);

            Graphics graphic;
            if (image.PixelFormat != PixelFormat.Indexed && image.PixelFormat != PixelFormat.Format8bppIndexed && image.PixelFormat != PixelFormat.Format4bppIndexed && image.PixelFormat != PixelFormat.Format1bppIndexed)
            {

                graphic = Graphics.FromImage(image);
            }
            else
            {

                Bitmap indexedImage = new Bitmap(image);
                graphic = Graphics.FromImage(indexedImage);

                // Draw the contents of the original bitmap onto the new bitmap.
                graphic.DrawImage(image, 0, 0, image.Width, image.Height);
                image = indexedImage;
            }
            graphic.SmoothingMode = SmoothingMode.AntiAlias & SmoothingMode.HighQuality;
            //This is the font for your watermark
            int size = 30; int opacity = 100;
            Font myFont = new Font("Arial", size, FontStyle.Bold, GraphicsUnit.Pixel);
            SolidBrush brush = new SolidBrush(Color.FromArgb(opacity, Color.Beige));

            //This gets the size of the graphic

            SizeF textSize = graphic.MeasureString(watermark, myFont);
            graphic.TranslateTransform(image.Width / 2, image.Height / 2);
            var angle = -45f;
            graphic.RotateTransform(angle);
            var x = -(textSize.Width / 2);
            var y = -(textSize.Height / 2);
            // Code for writing text on the image and showing its postion on images.
            //graphic.RotateTransform(45);
            PointF pointF = new PointF(x, y);

            graphic.DrawString(watermark, myFont, brush, pointF);

            using (MemoryStream memoryStream = new MemoryStream())
            {
                image.Save(memoryStream, GetImageFormat(PhysicalPath));
                imageBytes = memoryStream.ToArray();
            }
        }
        return imageBytes;
}

I don't know how to calculate what font size you need ahead of time (you might want to pre-calculate a bunch of scenarios and reference them) but you can measure the string to see if it will fit. — Crowcoder
– Crowcoder, Commented Oct 5, 2018 at 12:48
@Siavash Ghanbari: I have no problem with my code but just the watermark text appears very tiny when the image size is bigger. say like ("3840*2160). For that I need some way to define the watermark text based on the image size. So, the watermark text can be visible irrespective of the image size. — DonMax
– DonMax, Commented Oct 5, 2018 at 12:53

Siavash · Accepted Answer · 2018-10-05 13:24:51Z

6

you just need to change your size value, 30 is a fixed and change it to below code:

int countOfChar = Watermarktext.Length;
int size = (image.Width + image.Height / 2) / countOfChar;

I tested your code with a little changes, and that worked for all image sizes and dimensions.

answered Oct 5, 2018 at 13:24

Siavash

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2 Comments

DonMax Over a year ago

I have done little changes to your code and it works fine for all size images. int size = ((image.Width + image.Height) / 2) / countOfChar;

Mohiyo Deen Over a year ago

Don't know your but my watermark text on my images is still not dynamic... it goes out of the image.

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