Print bitmap full page width using ESC/POS

Question

I am currently implementing Android PrintService, that is able to print PDFs via thermal printers. I managed to convert PDF to bitmap using PDFRenderer and I am even able to print the document.

The thing is, the document (bitmap) is not full page width.

I am receiving the document in 297x420 resolution and I am using printer with 58mm paper.

This is how I process the document (written in C#, using Xamarin):

// Create PDF renderer
var pdfRenderer = new PdfRenderer(fileDescriptor);  

// Open page
PdfRenderer.Page page = pdfRenderer.OpenPage(index);

// Create bitmap for page
Bitmap bitmap = Bitmap.CreateBitmap(page.Width, page.Height, Bitmap.Config.Argb8888);

// Now render page into bitmap
page.Render(bitmap, null, null, PdfRenderMode.ForPrint);

And then, converting the bitmap into ESC/POS:

// Initialize result
List<byte> result = new List<byte>();

// Init ESC/POS
result.AddRange(new byte[] { 0x1B, 0x33, 0x21 });

// Init ESC/POS bmp commands (will be reapeated)
byte[] escBmp = new byte[] { 0x1B, 0x2A, 0x01, (byte)(bitmap.Width % 256), (byte)(bitmap.Height / 256) };

// Iterate height
for (int i = 0; i < (bitmap.Height / 24 + 1); i++)
{
    // Add bitmapp commands to result
    result.AddRange(escBmp);

    // Init pixel color
    int pixelColor;

    // Iterate width
    for (int j = 0; j < bitmap.Width; j++)
    {
        // Init data
        byte[] data = new byte[] { 0x00, 0x00, 0x00 };

        for (int k = 0; k < 24; k++)
        {
            if (((i * 24) + k) < bitmap.Height)
            {
                // Get pixel color
                pixelColor = bitmap.GetPixel(j, (i * 24) + k);

                // Check pixel color
                if (pixelColor != 0)
                {
                    data[k / 8] += (byte)(128 >> (k % 8));
                }
            }
        }

        // Add data to result
        result.AddRange(data);
    }

    // Add some... other stuff
    result.AddRange(new byte[] { 0x0D, 0x0A });
}

// Return data
return result.ToArray();

Current result looks like this:

Thank you all in advance.

You want a full page print? – FreakyAli May 30 '18 at 10:03 — FreakyAli, May 30 '18 at 10:03
Yes, sorry. Fixed the title and some text. – Filip Matys May 30 '18 at 10:06 — Filip Matys, May 30 '18 at 10:06

score 2 · Accepted Answer · answered May 30 '18 at 11:54

There is no magic "scale-to-page-width" command in the ESC/POS command-set, you need to know the max width of your printer, available in the manual, and then you can:

Double the width and height for some image output commands -- You are using ESC *, which supports low-density, but height and width change in different ratios.
Render the PDF wider to begin with - match the Bitmap size to the printer page width, and not the PDF page width. The same problem is solved at PDFrenderer setting scale to screen
You can also simply stretch the image before you send it, if you are happy with the low quality. See: How to Resize a Bitmap in Android?

Aside, your ESC * implementation is incorrect. There are two bytes for the width- Check the ESC/POS manual for the correct usage, or read over the correct implementations in PHP or Python that I've linked in another question: ESC POS command ESC* for printing bit image on printer

Scaling did the trick, thank you. Was trying it before, but was getting random characters out of the printer. Found a treshold and it now prints just fine :). — Filip Matys, May 30 '18 at 13:25

Print bitmap full page width using ESC/POS

1 Answers1