How can I print an image on a Bluetooth printer in Android?

The question:

I have to print some data on thermal bluetooth printer, I’m doing with this:

String message="abcdef any message 12345";
byte[] send;
send = message.getBytes();

It works well for text, but not for images. I think I need to get the byte[] of the image data. I tried getting the data of the image this way:

Bitmap bitmap=BitmapFactory.decodeResource(getResources(), R.drawable.qrcode);
ByteArrayOutputStream stream=new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.PNG, 90, stream);
byte[] image=stream.toByteArray();

Unfortunately the printer prints a lot of strange characters (approx. 50 cm of paper). I don’t know how to print the image.

I would like to try getting the pixels of the bitmap and next converting it to a byte[] and sending it, but i don’t know how to do it.



After so much time, i’m doing this: I have a method called print_image(String file), the which gets the path of the image that i want to print:

private void print_image(String file) {
    File fl = new File(file);
    if (fl.exists()) {
        Bitmap bmp = BitmapFactory.decodeFile(file);

        int offset = 0;
        while (offset < bmp.getHeight()) {
            for (int x = 0; x < bmp.getWidth(); ++x) {

                for (int k = 0; k < 3; ++k) {

                    byte slice = 0;
                    for (int b = 0; b < 8; ++b) {
                        int y = (((offset / 8) + k) * 8) + b;
                        int i = (y * bmp.getWidth()) + x;
                        boolean v = false;
                        if (i < dots.length()) {
                            v = dots.get(i);
                        slice |= (byte) ((v ? 1 : 0) << (7 - b));
            offset += 24;

    } else {
        Toast.makeText(this, "file doesn't exists", Toast.LENGTH_SHORT)

I did it based on this post

This is the class PrinterCommands:

public class PrinterCommands {
public static final byte[] INIT = {27, 64};
public static byte[] FEED_LINE = {10};

public static byte[] SELECT_FONT_A = {27, 33, 0};

public static byte[] SET_BAR_CODE_HEIGHT = {29, 104, 100};
public static byte[] PRINT_BAR_CODE_1 = {29, 107, 2};
public static byte[] SEND_NULL_BYTE = {0x00};

public static byte[] SELECT_PRINT_SHEET = {0x1B, 0x63, 0x30, 0x02};
public static byte[] FEED_PAPER_AND_CUT = {0x1D, 0x56, 66, 0x00};

public static byte[] SELECT_CYRILLIC_CHARACTER_CODE_TABLE = {0x1B, 0x74, 0x11};

public static byte[] SELECT_BIT_IMAGE_MODE = {0x1B, 0x2A, 33, -128, 0};
public static byte[] SET_LINE_SPACING_24 = {0x1B, 0x33, 24};
public static byte[] SET_LINE_SPACING_30 = {0x1B, 0x33, 30};

public static byte[] TRANSMIT_DLE_PRINTER_STATUS = {0x10, 0x04, 0x01};
public static byte[] TRANSMIT_DLE_OFFLINE_PRINTER_STATUS = {0x10, 0x04, 0x02};
public static byte[] TRANSMIT_DLE_ERROR_STATUS = {0x10, 0x04, 0x03};
public static byte[] TRANSMIT_DLE_ROLL_PAPER_SENSOR_STATUS = {0x10, 0x04, 0x04};

As is seen in the print_image method I’m calling a method, called convertBitmap, and im sending a bitmap, this is the code:

   public String convertBitmap(Bitmap inputBitmap) {

    mWidth = inputBitmap.getWidth();
    mHeight = inputBitmap.getHeight();

    convertArgbToGrayscale(inputBitmap, mWidth, mHeight);
    mStatus = "ok";
    return mStatus;


private void convertArgbToGrayscale(Bitmap bmpOriginal, int width,
        int height) {
    int pixel;
    int k = 0;
    int B = 0, G = 0, R = 0;
    dots = new BitSet();
    try {

        for (int x = 0; x < height; x++) {
            for (int y = 0; y < width; y++) {
                // get one pixel color
                pixel = bmpOriginal.getPixel(y, x);

                // retrieve color of all channels
                R =;
                G =;
                B =;
                // take conversion up to one single value by calculating
                // pixel intensity.
                R = G = B = (int) (0.299 * R + 0.587 * G + 0.114 * B);
                // set bit into bitset, by calculating the pixel's luma
                if (R < 55) {                       
                    dots.set(k);//this is the bitset that i'm printing



    } catch (Exception e) {
        // TODO: handle exception
        Log.e(TAG, e.toString());

This is the printer that i’m using, resolution: 8 dots/mm, 576 dots/line

And this is what I like to do (i did it with the same printer, but with an app downloaded from play store)
Image that I want to print

This is what i’m getting now
My printing trying

A closer part

enter image description here

A little part of the image can be seen, so I think that i’m closer to can print the image…

The image that i’m using is this (576×95):enter image description here

And this is the converted image (i’m converting it with the upper code):
converted image


So, the answer is: what I’m doing wrong?, I think that the error is in this command:

  public static byte[] SELECT_BIT_IMAGE_MODE = {0x1B, 0x2A, 33, -128, 0};

But, how can I calculate the correct values for my image?, thanks

The Solutions:

Below are the methods you can try. The first solution is probably the best. Try others if the first one doesn’t work. Senior developers aren’t just copying/pasting – they read the methods carefully & apply them wisely to each case.

Method 1

I solve it converting Bitmap to Byte array. Remember that your image must be black & white format.

For full source code:

enter image description here

 public void printPhoto() {
        try {
            Bitmap bmp = BitmapFactory.decodeResource(getResources(),
                byte[] command = Utils.decodeBitmap(bmp);
                Log.e("Print Photo error", "the file isn't exists");
        } catch (Exception e) {
            Log.e("PrintTools", "the file isn't exists");

Method 2

I also tried this and I got to my own solution and I think I figured out how the SELECT_BIT_IMAGE_MODE command works.

The command public static byte[] SELECT_BIT_IMAGE_MODE = {0x1B, 0x2A, 33, 255, 3}; in the class PrinterCommands is the POS Command for image printing.

The first two are pretty standard, the next three determine the mode and the dimensions of the image to be printed. For the sake of this solution, let’s just assume that the second element (33, we are indexed zero) is always 33.

The last two elements of that byte[] refers to the Width (in pixels) property of the image that you want to print, element 3 is sometimes referred to as nL and element 4 is sometimes referred to as nH. They are actually both referring to the Width, nL is the Low Byte while nH is the High Byte. This means that we can have at the most an image with a width of 1111 1111 1111 1111b (binary) which is 65535d (decimal), though I haven’t tried it yet. If nL or nH aren’t set to the proper values, then there will be trash characters printed along with the image.

Somehow, Android docs tells us that the limits of the value for a byte in a byte array is -128 and +127, when I tried to put in 255, Eclipse asked me to cast it to Byte.

Anyway, going back to nL and nW, for your case, you have an image with width 576, if we convert 576 to Binary, we get two bytes which would go like:

0000 0010 0100 0000

In this case, the Low Byte is 0100 0000 while the High Byte is 0000 0010. Convert it back to decimal and we get nL = 64 and nH = 2.

In my case, I printed an image that has width of 330px, converting 330 to binary we get:

0000 0001 0100 1010

In this case now, the Low Byte is 0100 1010 and the High Byte is 0000 0001. Converting to decimal, we get nL = 74 and nH = 1.

For more information, look at these documentation/tutorials:

Star Asia Mobile Printer Documentation

ECS-POS programming guide – really extensive

Another Documentation

The expanded version of the code above, with more explanation

Explanation of the code above

Hope these helps.

Method 3

Solved!, I was doing a wrong printer initializing… The corect way is:

 public static byte[] SELECT_BIT_IMAGE_MODE = {0x1B, 0x2A, 33, 255, 3};

So, by this way the image is printed completely fine

Method 4

EDIT: Update based on reading your question:

I will assume that the printer you are printing to is the same as above, i.e. the Rego Thermal Printer. This, as you note, support the ESC/POS Page Description Language.

Printers interpret data streamed to them as either a marked up document (in a similar way to how browser interpret HTML). In some cases, the printer literally runs the document as a program (eg PostScript). Link: Page Description Languages.

Common languages are:

You need to read the specifications for your printer to determine which language to use – if you need to support any printer, then you have a very large job ahead of you 🙁

In ESC/POS, you will need to use the GS v 0 command (documented on p33). You do this by sending the the characters 0x1D7630 across the serial link, followed by a set of arguments:

ASCII:       Gs   v  0 
Decimal:     29 118 48 m xL xH yL yH [d]k 
Hexadecimal: 1D  76 30 m xL xH yL yH [d]k 

Parameter definitions:

  • m:
    • 0,48: normal mode (1:1 scale)
    • 1,49: double-width
    • 2,50: double-height
    • 3,51: double-width + double-height
  • xL, xH specifies (xL + xH × 256) bytes in horizontal direction for the bit image.
  • yL, yH specifies (yL + yH × 256) dots in vertical direction for the bit image.
  • [d]k specifies the bit image data (raster format).
  • k indicates the number of bit image data. k is an explanation parameter; therefore, it does not need to be transmitted.


  • When data [d]k is 1 specifies a bit printed to 1 and not printed to 0.
  • If a raster bit image exceeds one line of print area, the excess data is not printed.
  • This command executes paper feed for amount needed for printing the bit image regardless of the settings by ESC 2 or ESC 3.
  • After printing the bit image, this command sets the print position to the beginning of the line, and clears up the buffer.
  • When this command is executed, the data is transmitted and printed synchronously. So no other printing command is required.

There are several more extensive expositions:

Unfortunately there is no printer API in Android. If you feel strongly about this, do follow these issues:

Method 5

I am new to ESC/POS and am struggling with it. I came across this page which seems to have some useful functions:
It’s in Chinese though, but might be worth going through. If anybody figures it out, I would like to get enlightened too…

Method 6

I know for evolute and AMDL bluetooth printers.First Read the protocol defination document of the printer that tells you what specific bytes you need for the device-

public void connect() throws Exception 

    BluetoothDevice printer = BluetoothAdapter.getDefaultAdapter().getRemoteDevice(connParams);

    Method m = printer.getClass().getMethod("createInsecureRfcommSocket",new Class[] { int.class });
    sock = (BluetoothSocket)m.invoke(printer, Integer.valueOf(1));


After connecting through the above code you get the outputstream of the socket.Then convert your image to the corresponding byte through the tool provided with the printer you get something like

public byte[] Packet1={

where 8A is starting byte C6 is mode byte (different for smart card , swipe and fingerprint) , 94 is font byte and last byte 04 is the end byte telling the hardware that this is end of the packet.Depending on size of the image you get several of these packets of length 256 byte (most printer).Write them to the outputStream.


Method 7

This works for me:

BitmapFactory.Options options = new BitmapFactory.Options();
options.inTargetDensity = 200;
options.inDensity = 200;
Bitmap bmp = BitmapFactory.decodeResource(context.getResources(), img, options);

Before using the BitmapFactory.Options, I was able to print only 60X60 image size, now i can print images of greater size as well.

Method 8

use this code:

public static void print(Context context) {

    String examplePath = "file:///sdcard/dcim/Camera/20111210_181524.jpg";

    Intent sendIntent = new Intent(Intent.ACTION_SEND);
    sendIntent.putExtra(Intent.EXTRA_SUBJECT, "Photo");
    sendIntent.putExtra(Intent.EXTRA_STREAM, Uri.parse(examplePath));
    sendIntent.putExtra(Intent.EXTRA_TEXT, "Enjoy the photo");
    context.startActivity(Intent.createChooser(sendIntent, "Email:"));

All methods was sourced from or, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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