Converting PNG image to ZPL code

Question

I need to print a PNG image onto a label with a ZPL printer. The idea is to convert the PNG image to a monochrome one and then generate the necessary ZPL code with the image data to print the image.

After some googling and coding, I have a piece of code that does just that. The generated ZPL code seems fine on labelary (http://labelary.com).

The code for generating the ZPL code was mostly taken from here --> How to optimize ASCII HEX for BMP to ZPL as using in Labelary

Unfortunately, when trying to print a label with the generated ZPL code, it comes out like this: Not supposed to look like this

Image should look like this: ImageToConvert

The code that i use is this:

static void Main(string[] args)
    {

        // 1. Convert Image to monochrome bmp
        string bitmapFilePath = @"somepath.bmp";
        Bitmap imageToConvert = new Bitmap(bitmapFilePath);
        var rectangle = new Rectangle(0, 0, imageToConvert.Width, imageToConvert.Height);
        Bitmap monochromeImage = imageToConvert.Clone(rectangle, PixelFormat.Format1bppIndexed);

        // Mirror image
        monochromeImage.RotateFlip(RotateFlipType.Rotate180FlipX);

        // Save mono image            
        monochromeImage.Save("somePathMono.bmp", ImageFormat.Bmp);

        // 2. Convert to ZPL
        ConvertImage();   

    }

    public static void ConvertImage()
    {
        string bitmapFilePath = "somePathMono.bmp";
        int w, h;
        Bitmap b = new Bitmap(bitmapFilePath);
        w = b.Width; h = b.Height;
        byte[] bitmapFileData = System.IO.File.ReadAllBytes(bitmapFilePath);
        int fileSize = bitmapFileData.Length;

        int bitmapDataOffset = int.Parse(bitmapFileData[10].ToString()); ;
        int width = w; // int.Parse(bitmapFileData[18].ToString()); ;
        int height = h; // int.Parse(bitmapFileData[22].ToString()); ;
        int bitsPerPixel = int.Parse(bitmapFileData[28].ToString()); 
        int bitmapDataLength = bitmapFileData.Length - bitmapDataOffset;
        double widthInBytes = Math.Ceiling(width / 8.0);

        while (widthInBytes % 4 != 0)
        {
            widthInBytes++;
        }

        // Copy over the actual bitmap data without header data            
        byte[] bitmap = new byte[bitmapDataLength];

        Buffer.BlockCopy(bitmapFileData, bitmapDataOffset, bitmap, 0, bitmapDataLength);           

        // Invert bitmap colors
        for (int i = 0; i < bitmapDataLength; i++)
        {
            bitmap[i] ^= 0xFF;
        }             

        // Create ASCII ZPL string of hexadecimal bitmap data
        string ZPLImageDataString = BitConverter.ToString(bitmap);            
        ZPLImageDataString = ZPLImageDataString.Replace("-", string.Empty);

        // Add new line every 1023 chars characters
        string ZPLImageDataStringWithNewLine = SpliceText(ZPLImageDataString, 1023);            

        // Create ZPL command to print image
        string ZPLCommand = string.Empty;

        ZPLCommand += "^XA";
        ZPLCommand += "^FO20,20";
        ZPLCommand +=
        "^GFA," +
        bitmapDataLength.ToString() + "," +
        bitmapDataLength.ToString() + "," +
        widthInBytes.ToString() + "," +
        System.Environment.NewLine +
        ZPLImageDataStringWithNewLine;

        ZPLCommand += "^XZ";

        System.IO.StreamWriter sr = new System.IO.StreamWriter("zplCodePath", false, System.Text.Encoding.Default);

        sr.Write(ZPLCommand);
        sr.Close();       
    }

    public static string SpliceText(string text, int lineLength)
    {
        return Regex.Replace(text, "(.{" + lineLength + "})", "$1" + Environment.NewLine);
    }

We use the Zebra ZT 410 printer

Can someone help me figure out what the problem could be? I'm out of ideas at this point.

Thanks!

UPDATE: Seems like the problem is the newline that I put after every x characters in the image data. I don't understand why. My code works perfectly for smaller image (where I don't have to put new lines), but for big images with long imagedata strings it does not print if I don't put the new lines.

Any help would be appreciated!

Answer 1

Because I had such issue with the ZPL guide and various references providing different solutions (that never seemed to fully work with my use-case) I created a simple .net core application which takes a label image and converts it to ZPL, either to a file (if output is provided) or directly to the console so it's pipeable in bash scripts.

Answer 2

I was facing same issue, use online tool to convert your png/jpeg to ZPL monochrome format for print and verify your ZPL code on viewer