How to add image to pdf with using bitmap, itext, and chart and rendering more detail (pixels or dpi)?

Question

Goal

I need to increase the quality of the bitmap that is being added to a pdf. I have a 300dpi image, but looks really bad when itextsharp adds it to pdf.

Description

I am working on a project which takes a bitmap and writes it to a pdf using itextSharp. The problem is that the project makes a graph, saves it as a bitmap, writes it to the pdf, and the graph appears to be low quality. I am unable to attach the picture here of what is being graphed, but will do my best to describe what is going on. Here is the code below:

//Declare chart object 
private static System.Windows.Forms.DataVisualization.Charting.Chart chart_runs;

//Start the PDF Document
Document pdfDocument = new Document(PageSize.LETTER);

private static System.Drawing.Bitmap GetChartBitmap()
{

        chart_runs.Width = 2269;
        chart_runs.Height = 1406;

        System.Drawing.Bitmap bitmap1 = new System.Drawing.Bitmap(2269, 1406);
        bitmap1.SetResolution(300, 300);
        chart_runs.DrawToBitmap(bitmap1, new System.Drawing.Rectangle(0, 0, 2269, 1406));

        string path = System.IO.Path.GetTempPath();

        bitmap1.Save(path + @"\Image.png");
        return bitmap1;

            }

Here is how the bitmap and image is added to the pdf.

        System.Drawing.Bitmap img = GetChartBitmap();
        img.Dispose();
        string path = System.IO.Path.GetTempPath();
        iTextSharp.text.Image imag
            = iTextSharp.text.Image.GetInstance(path + @"\Image.bmp");

        //imag.ScaleAbsolute(chart_runs.Width, chart_runs.Height);
        //imag.ScaleToFit(550, 330);
          imag.ScaleAbsolute(550, 350);
        //imag.ScaleAbsolute(650, 450);
        //imag.ScaleAbsolute(100f, 100f);

        pdfDocument.Add(imag);

        pdfDocument.Close();
        pdfDocument.Dispose();

Attempts

I have spent considerable time trying to fix this, here are some of the highlights.

• At first, it was believed this was a DPI issue. However, when I made the bitmap (and itext image) 300DPI, no quality difference was noticed.
• I then added more pixels by enlarging the targetBounds object above. This had the weird effect of shrinking my graph on my PDF? Why?
• I have attempted many manipulations with itext.scale functions as I found here.
• Another justification why I am trying to make my bitmap larger is on here.

As I said above, I seem to be making my image even smaller with the current approach. I am just trying to increase the quality of the bitmap so when people print it off or zoom in on the pdf it doesn't look terrible. I appreciate any help.

Answer 1

Not an answer yet

Here's a very simple image generating function just for testing purposes, it should be fairly self-explanatory:

private static byte[] CreateImage(string text, int fontSize, int width, int height) {
    using (var b = new Bitmap(width, height)) {
        using (var g = Graphics.FromImage(b)) {
            using(var br = new SolidBrush(System.Drawing.Color.Red)){
                using (var f = new System.Drawing.Font("Arial Unicode MS", fontSize)) {
                    g.DrawString(text, f, br, 10, 10);
                    using (var ms = new System.IO.MemoryStream()) {
                        b.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp);
                        return ms.ToArray();
                    }
                }
            }
        }
    }
}

If you examine the PDF generated from the below code that uses the function above you'll see each image in the PDF gets progressively "better" and you can zoom in further before seeing jagged lines. Ultimately you're working with raster/bitmap files, however, so some pixelation will almost always eventually occur. The DPI listed is the "effective DPI" which is based on the assumption that the PDF will map 72 units into 1 inch of space (which is the PDF standard's default) and that it is printed at 100% resolution.

var testFile = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "test.pdf");

using (var fs = new FileStream(testFile, FileMode.Create, FileAccess.Write, FileShare.None)) {
    using (var doc = new Document()) {
        using (var writer = PdfWriter.GetInstance(doc, fs)) {
            doc.SetMargins(0, 0, 0, 0);
            doc.Open();


            var img1 = iTextSharp.text.Image.GetInstance(CreateImage("Hello", 24, 600, 50));
            doc.Add(img1); //72 DPI

            var img2 = iTextSharp.text.Image.GetInstance(CreateImage("Hello", 48, 1200, 100));
            img2.ScaleAbsolute(600, 50);
            doc.Add(img2); //144 DPI

            var img3 = iTextSharp.text.Image.GetInstance(CreateImage("Hello", 96, 2400, 200));
            img3.ScaleAbsolute(600, 50);
            doc.Add(img3); //288 DPI

            var img4 = iTextSharp.text.Image.GetInstance(CreateImage("Hello", 192, 4800, 400));
            img4.ScaleAbsolute(600, 50);
            doc.Add(img4); //576 DPI


            doc.Close();
        }
    }
}