PDF generated with iTextSharp adding image gets bad quality

Question

I have an image file that I need to pass to PDF and for this I am using the iTextSharp.

So I’m trying this way:

private static void Main(string[] args)
{
    using (var stream = new FileStream("document.pdf", FileMode.Create))
    {
        using (var document = new Document(PageSize.A4))
        {
            PdfWriter.GetInstance(document, stream);

            document.SetMargins(20, 20, 20, 20);
            document.AddCreationDate();
            document.Open();

            using (var picture = new Bitmap("model256.bmp"))
            {
                double percentage;
                if (picture.Height > picture.Width)
                    percentage = document.PageSize.Height / picture.Height;
                else
                    percentage = document.PageSize.Width / picture.Width;

                using (var newPicture = Util.ResizeImage(picture, 
                    Convert.ToInt32(picture.Width * percentage), 
                    Convert.ToInt32(picture.Height * percentage)))
                {
                    var image = iTextSharp.text.Image.GetInstance(newPicture, 
                        BaseColor.WHITE);
                    image.Alignment = Element.ALIGN_CENTER;

                    document.Add(image);
                    document.Close();
                }
            }
        }
    }
}

With this help to resize:

public static class Util
{
    public static Bitmap ResizeImage(Bitmap bitmap, int newWidth, int newHeight)
    {
        var width = bitmap.Width;
        var heigth = bitmap.Height;

        if (width > newWidth || heigth > newHeight)
        {
            if (width > heigth)
            {
                heigth = (heigth * newWidth) / width;
                width = 500;
            }
            else
            {
                width = (width * newHeight) / heigth;
                heigth = 500;
            }
        }

        var image = bitmap.GetThumbnailImage(width, heigth, null, new System.IntPtr(0));
        return new Bitmap(image);
    }
}

The format of the images is bmp.

Here are the images placed side by side for comparison

The stackoverflow editor resizes the images and so here it looks bad. But by clicking on both images it appears in full size and with the correct quality.

How to generate PDF with good image quality?

EDITION

---

Making use of Graphics

Using Graphics to try to improve the output image also had no improvements.

private static void Main(string[] args)
{
    using (var stream = new FileStream("document.pdf", FileMode.Create))
    {
        using (var document = new Document(PageSize.A4))
        {
            PdfWriter.GetInstance(document, stream);

            document.SetMargins(20, 20, 20, 20);
            document.AddCreationDate();
            document.Open();

            using (var picture = new Bitmap("original.bmp"))
            {
                var width = Convert.ToInt32(Math.Round(
                    document.PageSize.Width - 40));
                var height = Convert.ToInt32(Math.Round(
                    ((float)picture.Height / (float)picture.Width) * (width)));

                using (var newPicture = Util.RedimensionarImagem(
                    picture, width, height, PixelFormat.Format48bppRgb))
                {
                    var image = Image.GetInstance(newPicture, BaseColor.WHITE);
                    image.Alignment = Element.ALIGN_CENTER;

                    document.Add(image);
                    document.Close();
                }
            }
        }
    }
}

And the resize routine:

public static Image RedimensionarImagem(Image image, int width, int height, PixelFormat pf)
{
    if (image != null)
    {
        var newImage = new Bitmap(width, height, pf);
        using (var gr = Graphics.FromImage(newImage))
        {
            //gr.SmoothingMode = SmoothingMode.HighQuality;
            gr.InterpolationMode = InterpolationMode.HighQualityBicubic;
            //gr.PixelOffsetMode = PixelOffsetMode.HighQuality;
            gr.DrawImage(image, 0, 0, width, height);
            gr.Dispose();
            return newImage;
        }
    }
    return null;
}

Sample image:

Resizing by the object iTextSharp.text.Image

When using the original image, without resizing it, and resizing the object Image of iTextSharp I managed to get a little improvement.

In various attempts of resizing the image seeking the best conversion I found that still there was loss while passing the image to the Image of iTextSharp and then to the Document

But still presents a low-quality image!

Code:

using (var document = new Document(PageSize.A4))
{
    document.SetMargins(20, 20, 20, 20);
    document.AddCreationDate();
    document.Open();

    using (var picture = new Bitmap("original.bmp"))
    {
        var width = Convert.ToInt32(Math.Round(document.PageSize.Width - 40));
        var height = Convert.ToInt32(Math.Round(((float)picture.Height / (float)picture.Width) * (width)));

        using (var writer = PdfWriter.GetInstance(document, stream))
        {
            writer.SetPdfVersion(PdfWriter.PDF_VERSION_1_7);
            writer.CompressionLevel = PdfStream.NO_COMPRESSION;

            document.Open();

            var image = iTextSharp.text.Image.GetInstance(bitmap, BaseColor.WHITE);
            image.Alignment = Element.ALIGN_CENTER;

            image.SetDpi(600, 600);
            image.ScaleToFit(width, heigth);

            document.Add(image);
            document.Close();
        }
    }
}

Upshot

Answer 1

In your image resize method, you are using

var image = bitmap.GetThumbnailImage(width, heigth, null, new System.IntPtr(0));
return new Bitmap(image);

This method returns a thumbnail of the image passed. You should not use this.

Follows a function I use to resize image:

public static System.Drawing.Image RedimensionarImagem(System.Drawing.Image srcImage, int newWidth, int newHeight, PixelFormat pf)
{
    if (srcImage != null)
    {
        Bitmap newImage = new Bitmap(newWidth, newHeight, pf);
        using (Graphics gr = Graphics.FromImage((Image)newImage))
        {
            //gr.SmoothingMode = SmoothingMode.HighQuality;
            gr.InterpolationMode = InterpolationMode.HighQualityBicubic;
            //gr.PixelOffsetMode = PixelOffsetMode.HighQuality;
            gr.DrawImage(srcImage, 0, 0, newWidth, newHeight);// new Rectangle(0, 0, newWidth, newHeight));
            gr.Dispose();
            return (Image)newImage;
        }
    }
    else
        return null;

}

To execute the call:

var image = RedimensionarImagem(bitmap, width, height, PixelFormat.Format24bppRgb);

Getthumbnailimage method documentation: https://msdn.microsoft.com/pt-br/library/system.drawing.image.getthumbnailimage(v=vs.110). aspx