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

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(); mService.write(send); 

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.

Thanks

UPDATE:

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);         convertBitmap(bmp);         mService.write(PrinterCommands.SET_LINE_SPACING_24);          int offset = 0;         while (offset < bmp.getHeight()) {             mService.write(PrinterCommands.SELECT_BIT_IMAGE_MODE);             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));                     }                     mService.write(slice);                 }             }             offset += 24;             mService.write(PrinterCommands.FEED_LINE);             mService.write(PrinterCommands.FEED_LINE);                       mService.write(PrinterCommands.FEED_LINE);             mService.write(PrinterCommands.FEED_LINE);             mService.write(PrinterCommands.FEED_LINE);             mService.write(PrinterCommands.FEED_LINE);         }         mService.write(PrinterCommands.SET_LINE_SPACING_30);       } else {         Toast.makeText(this, "file doesn't exists", Toast.LENGTH_SHORT)                 .show();     } } 

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                 }                 k++;              }           }       } 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)

This is what i'm getting now

Closer:

Closer2:

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):

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

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 1

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

For full source code: https://github.com/imrankst1221/Thermal-Printer-in-Android

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

Answer 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.