Converting PNG image to ZPL code

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 (

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

(This is just a sample image.)

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

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

// 2. Convert to ZPL


public static void ConvertImage()
string bitmapFilePath = "somePathMono.bmp";
int w, h;
Bitmap b = new Bitmap(bitmapFilePath);
= 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)

// 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++)
[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," +
.ToString() + "," +
.ToString() + "," +
.ToString() + "," +
System.Environment.NewLine +

ZPLCommand += "^XZ";

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


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. Maybe I'm doing it completely wrong, and there is an easier ways. any help would be appreciated