picture scale with out quality loss

Question

I am not a C# developer (embedded developer with C) but I have been forced to do a project which requires me to add a barcode to a PNG and print it,

if the resolution of the picture is high, the picture will be printed huge, covering a couple of labels (the printer works in 2 labels per row and 7 columns for each print command, a total of 14 labels)

now when I resize it, the picture will fit, however, the Quality will drop dramatically, and it's unreadable

this is the code I am using (The code is from Stackoverflow somewhere)

static Bitmap ScaleImage(Bitmap bmp, int maxWidth, int maxHeight)
{
    var ratioX = (double)maxWidth / bmp.Width;
    var ratioY = (double)maxHeight / bmp.Height;
    var ratio = Math.Min(ratioX, ratioY);

    var newWidth = (int)(bmp.Width * ratio);
    var newHeight = (int)(bmp.Height * ratio);

    var newImage = new Bitmap(newWidth, newHeight);

    using (var graphics = Graphics.FromImage(newImage))
        graphics.DrawImage(bmp, 0, 0, newWidth, newHeight);

    return newImage;
}

private void button1_Click(object sender, EventArgs e)
{
    var image = new Bitmap("C:\\Users\\gilani\\Desktop\\BarCodeCreator\\sad2.bmp");
    pictureBox1.Image = ScaleImage(image, 100, 80); 
}
private void button2_Click(object sender, EventArgs e)
{
    PrintDialog print = new PrintDialog();
    PrintDocument doc = new PrintDocument();
    doc.PrintPage += Doc_PrintPage;
    print.Document = doc;

    if (print.ShowDialog(this) == DialogResult.OK)
    {
        doc.Print();
    }
}

private void Doc_PrintPage(object sender, PrintPageEventArgs e)
{
    int start_right = 32;
    int start_Top = 0;
    Bitmap bitmp = new Bitmap(pictureBox1.Image), pictureBox1.Image.Height));
    e.Graphics.DrawImage(bitmp, start_right, start_Top);
    bitmp.Dispose();
}

I need a way to preserve the Resolution/ Quality but print in much smaller size (probably its caled scale) I might even be going the whole road wrong, please inform me if I need to take another way

Answer 1

The easiest thing to try is to use a more sophisticated interpolation mode. HighQualityBicubic should yield best results.

Change your code to:

using (var graphics = Graphics.FromImage(newImage)) 
{
    graphics.SetInterpolationMode(InterpolationMode.HighQualityBicubic);
    graphics.DrawImage(bmp, 0, 0, newWidth, newHeight);
}

You can find more information here.

Answer 2

I would try using .SetResolution to set the dpi to a higher value.

When displaying an image on the screen we normally want to map image pixels to screen pixels 1:1. But printers does not really have "pixles" at all, so you can configure how large a image pixel should be on the paper by setting the dpi. Images often have 96dpi since that should result in 1:1 mapping on a screen, but printers often have dpi of 200-300.

You might also need to adjust things like PageSettings.PrinterResolution on your printer document to get the best possible resolution from your printer.