Leonardo Sapuy Leonardo Sapuy - 1 year ago 810
Java Question

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

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
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
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 = Color.red(pixel);
G = Color.green(pixel);
B = Color.blue(pixel);
// 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 (576x95):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

Answer Source

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

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