How to convert image to zpl code for printing using zebra printer?

I solved the problem and I am posting the answer so that other people can take benefit from the solution. The bitmap image can be converted to zpl code using following converter class.

public class ZPLConverter {
    private int blackLimit = 380;
    private int total;
    private int widthBytes;
    private boolean compressHex = false;
    private static Map<Integer, String> mapCode = new HashMap<Integer, String>();

    {
        mapCode.put(1, "G");
        mapCode.put(2, "H");
        mapCode.put(3, "I");
        mapCode.put(4, "J");
        mapCode.put(5, "K");
        mapCode.put(6, "L");
        mapCode.put(7, "M");
        mapCode.put(8, "N");
        mapCode.put(9, "O");
        mapCode.put(10, "P");
        mapCode.put(11, "Q");
        mapCode.put(12, "R");
        mapCode.put(13, "S");
        mapCode.put(14, "T");
        mapCode.put(15, "U");
        mapCode.put(16, "V");
        mapCode.put(17, "W");
        mapCode.put(18, "X");
        mapCode.put(19, "Y");
        mapCode.put(20, "g");
        mapCode.put(40, "h");
        mapCode.put(60, "i");
        mapCode.put(80, "j");
        mapCode.put(100, "k");
        mapCode.put(120, "l");
        mapCode.put(140, "m");
        mapCode.put(160, "n");
        mapCode.put(180, "o");
        mapCode.put(200, "p");
        mapCode.put(220, "q");
        mapCode.put(240, "r");
        mapCode.put(260, "s");
        mapCode.put(280, "t");
        mapCode.put(300, "u");
        mapCode.put(320, "v");
        mapCode.put(340, "w");
        mapCode.put(360, "x");
        mapCode.put(380, "y");
        mapCode.put(400, "z");
    }

    public String convertFromImage(Bitmap image, Boolean addHeaderFooter) {
        String hexAscii = createBody(image);
        if (compressHex) {
            hexAscii = encodeHexAscii(hexAscii);
        }

        String zplCode = "^GFA," + total + "," + total + "," + widthBytes + ", " + hexAscii;

        if (addHeaderFooter) {
            String header = "^XA " + "^FO0,0^GFA," + total + "," + total + "," + widthBytes + ", ";
            String footer = "^FS" + "^XZ";
            zplCode = header + zplCode + footer;
        }
        return zplCode;
    }

    private String createBody(Bitmap bitmapImage) {
        StringBuilder sb = new StringBuilder();
        int height = bitmapImage.getHeight();
        int width = bitmapImage.getWidth();
        int rgb, red, green, blue, index = 0;
        char auxBinaryChar[] = {'0', '0', '0', '0', '0', '0', '0', '0'};
        widthBytes = width / 8;
        if (width % 8 > 0) {
            widthBytes = (((int) (width / 8)) + 1);
        } else {
            widthBytes = width / 8;
        }
        this.total = widthBytes * height;
        for (int h = 0; h < height; h++) {
            for (int w = 0; w < width; w++) {
                rgb = bitmapImage.getPixel(w, h);
                red = (rgb >> 16) & 0x000000FF;
                green = (rgb >> 8) & 0x000000FF;
                blue = (rgb) & 0x000000FF;
                char auxChar = '1';
                int totalColor = red + green + blue;
                if (totalColor > blackLimit) {
                    auxChar = '0';
                }
                auxBinaryChar[index] = auxChar;
                index++;
                if (index == 8 || w == (width - 1)) {
                    sb.append(fourByteBinary(new String(auxBinaryChar)));
                    auxBinaryChar = new char[]{'0', '0', '0', '0', '0', '0', '0', '0'};
                    index = 0;
                }
            }
            sb.append("\n");
        }
        return sb.toString();
    }

    private String fourByteBinary(String binaryStr) {
        int decimal = Integer.parseInt(binaryStr, 2);
        if (decimal > 15) {
            return Integer.toString(decimal, 16).toUpperCase();
        } else {
            return "0" + Integer.toString(decimal, 16).toUpperCase();
        }
    }

    private String encodeHexAscii(String code) {
        int maxlinea = widthBytes * 2;
        StringBuilder sbCode = new StringBuilder();
        StringBuilder sbLinea = new StringBuilder();
        String previousLine = null;
        int counter = 1;
        char aux = code.charAt(0);
        boolean firstChar = false;
        for (int i = 1; i < code.length(); i++) {
            if (firstChar) {
                aux = code.charAt(i);
                firstChar = false;
                continue;
            }
            if (code.charAt(i) == '\n') {
                if (counter >= maxlinea && aux == '0') {
                    sbLinea.append(",");
                } else if (counter >= maxlinea && aux == 'F') {
                    sbLinea.append("!");
                } else if (counter > 20) {
                    int multi20 = (counter / 20) * 20;
                    int resto20 = (counter % 20);
                    sbLinea.append(mapCode.get(multi20));
                    if (resto20 != 0) {
                        sbLinea.append(mapCode.get(resto20)).append(aux);
                    } else {
                        sbLinea.append(aux);
                    }
                } else {
                    sbLinea.append(mapCode.get(counter)).append(aux);
                }
                counter = 1;
                firstChar = true;
                if (sbLinea.toString().equals(previousLine)) {
                    sbCode.append(":");
                } else {
                    sbCode.append(sbLinea.toString());
                }
                previousLine = sbLinea.toString();
                sbLinea.setLength(0);
                continue;
            }
            if (aux == code.charAt(i)) {
                counter++;
            } else {
                if (counter > 20) {
                    int multi20 = (counter / 20) * 20;
                    int resto20 = (counter % 20);
                    sbLinea.append(mapCode.get(multi20));
                    if (resto20 != 0) {
                        sbLinea.append(mapCode.get(resto20)).append(aux);
                    } else {
                        sbLinea.append(aux);
                    }
                } else {
                    sbLinea.append(mapCode.get(counter)).append(aux);
                }
                counter = 1;
                aux = code.charAt(i);
            }
        }
        return sbCode.toString();
    }

    public void setCompressHex(boolean compressHex) {
        this.compressHex = compressHex;
    }

    public void setBlacknessLimitPercentage(int percentage) {
        blackLimit = (percentage * 768 / 100);
    }

   }

Example usage: You need to convert the your image to bitmap, convert to monochrome image and do hex acii conversion. The generated zpl code can be checked at labelary viewer.

public class Utils {

    public static String getZplCode(Bitmap bitmap, Boolean addHeaderFooter) {
        ZPLConverter zp = new ZPLConverter();
        zp.setCompressHex(true);
        zp.setBlacknessLimitPercentage(50);
        Bitmap grayBitmap = toGrayScale(bitmap);
        return zp.convertFromImage(grayBitmap, addHeaderFooter);
    }

    public static Bitmap toGrayScale(Bitmap bmpOriginal) {
        int width, height;
        height = bmpOriginal.getHeight();
        width = bmpOriginal.getWidth();

        Bitmap grayScale = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        Canvas c = new Canvas(grayScale);
        Paint paint = new Paint();
        ColorMatrix cm = new ColorMatrix();
        cm.setSaturation(0);
        ColorMatrixColorFilter f = new ColorMatrixColorFilter(cm);
        paint.setColorFilter(f);
        c.drawBitmap(bmpOriginal, 0, 0, paint);
        return grayScale;
    }
}

The converter code has been referenced from here and added support for android use.