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Tom Marien

Passionate .NET/Node Developer, Team Leader, living in Belgium

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Our current project, has the ability to generate and combine EPL labels from different sources. One of the scenarios required to embed an image (png) into a generated label.


GW - Direct Graphic Write command

Description Use this command to load binary graphic data directly into the Image Buffer memory for immediate printing. The printer does not store graphic data sent directly to the image buffer.

The graphic data is lost when the image has finished printing, power is removed or the printer is reset. Commands that size (Q and q) or clear (N and M) the image buffer will also remove graphic image data.

Syntax GWp1,p2,p3,p4,DATA

  • p1 Horizontal start position (X) in dots.
  • p2 Vertical start position (Y) in dots.
  • p3 Width of graphic in bytes. Eight (8) dots = one (1) byte of data.
  • p4 Length of graphic in dots (or print lines)
  • DATA Raw binary data without graphic file formatting. Data must be in bytes. Multiply the width in bytes (p3) by the number of print lines (p4) for the total amount of graphic data. The printer automatically calculates the exact size of the data block based upon this formula.

The challenge

The challenge here was to figure out what they exactly mean by Raw binary data without graphic file formatting!

So after some googling a colleague of mine found the following working solution on CodeProject and adapted it to our needs.

using System;
using System.Drawing;
using System.IO;
using System.Text;

private static string SendImageToPrinter(int top, int left, Bitmap bitmap)
    using (MemoryStream ms = new MemoryStream())
    using (BinaryWriter bw = new BinaryWriter(ms, Encoding.ASCII))
        //we set p3 parameter, remember it is Width of Graphic in bytes,
        //so we divive the width of image and round up of it
        int P3 = (int)Math.Ceiling((double)bitmap.Width / 8);
        ("GW{0},{1},{2},{3},", top, left, P3, bitmap.Height)));
        //the width of matrix is rounded up multi of 8
        int canvasWidth = P3 * 8;
        //Now we convert image into 2 dimension binary matrix by 2 for loops below,
        //in the range of image, we get colour of pixel of image,
        //calculate the luminance in order to set value of 1 or 0
        //otherwise we set value to 1
        //Because P3 is set to byte (8 bits), so we gather 8 dots of this matrix,
        //convert into a byte then write it to memory by using shift left operator <<
        //e,g 1 << 7  ---> 10000000
        //    1 << 6  ---> 01000000
        //    1 << 3  ---> 00001000
        for (int y = 0; y < bitmap.Height; ++y)     //loop from top to bottom
            for (int x = 0; x < canvasWidth; )       //from left to right
                byte abyte = 0;
                for (int b = 0; b < 8; ++b, ++x)     //get 8 bits together and write to memory
                    int dot = 1;                     //set 1 for white,0 for black
                    //pixel still in width of bitmap,
                    //check luminance for white or black, out of bitmap set to white
                    if (x < bitmap.Width)
                        Color color = bitmap.GetPixel(x, y);
                        int luminance = (int)((color.R * 0.3) + (color.G * 0.59) + (color.B * 0.11));
                        dot = luminance > 127 ? 1 : 0;
                    abyte |= (byte)(dot << (7 - b)); //shift left,
                    //then OR together to get 8 bits into a byte
        //reset memory
        ms.Position = 0;
        //get encoding, I have no idea why encode page of 1252 works and fails for others
        return Encoding.GetEncoding(1252).GetString(ms.ToArray());

The problem

After analyzing the performance of our code under high load, we came to the conclusion that this extraction was actually really slowing the entire process down. It took around 1.5 seconds on average for a 10KB image (caused by usage of GetPixel).

What does it do?

  • Extracts raw binary data
  • Transforms the image into black and white
  • Adds a white overlay over parts that actually are out of bounds

What we needed?

  • Extract the raw binary data

As we already had an image within bounds which was already black and white (greyscale) in format1bppindexed format.

Extract raw binary fast (avg 84ms on 10KB file)

using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;

private static byte[] GetRawPixelData(Image image)
    using (var bitmap = (Bitmap) image)
        var bitmapData = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, PixelFormat.Format1bppIndexed);
            var length = bitmapData.Stride*bitmapData.Height;
            byte[] bytes = new byte[length];

            // Copy bitmap to byte[]
            Marshal.Copy(bitmapData.Scan0, bytes, 0, length);

            return bytes;
            // Make sure we unlock no matter what

Conversion to black and white (greyscale)

using System.Drawing;
using System.Drawing.Imaging;

public void ConvertToGrayscale(Image image)
    using (Bitmap bitmap = new Bitmap(image.Width, image.Height))
        using (var g = Graphics.FromImage(bitmap))
            //create the grayscale ColorMatrix
            var colorMatrix = new ColorMatrix(
                    new[] {.3f, .3f, .3f, 0, 0},
                    new[] {.59f, .59f, .59f, 0, 0},
                    new[] {.11f, .11f, .11f, 0, 0},
                    new float[] {0, 0, 0, 1, 0},
                    new float[] {0, 0, 0, 0, 1}

            //create some image attributes
            ImageAttributes attributes = new ImageAttributes();

            //set the color matrix attribute

            //draw the original image on the new image
            //using the grayscale color matrix
            g.DrawImage(image, new Rectangle(0, 0, image.Width, image.Height),
                0, 0, image.Width, image.Height, GraphicsUnit.Pixel, attributes);