Convert /assets/image.png to byte[]

Question

How to convert /assets/image.png to byte[] ?

I've tried like that (based on solution found on SO):

public void printimage(View view) {
    AssetManager assetManager = getAssets();
    InputStream inputStream = null;

    try {
        inputStream = assetManager.open("logo_print.png");
        byte[] bytesLogo = IOUtils.toByteArray(inputStream);

        int ret = printer.printImage(bytesLogo);

        if (ret < 0) {
            Toast(context, "printimage fail");
        }
        Toast(context, "image printed :)");

    }
    catch (IOException e){
        Log.e("message: ", e.getMessage());
        Toast(context, "printimage: convert image to Bytes fail");
    }
}

printImage — is declared in package like this:

public class Cprinter {
    public native int printImage(byte[] bytes);
}

But application crashes on print printimage(), error is "Native method not found: android.pt.Cprinter.printImage:([B)I"

I've converted byte to string (bytesLogo.toString()), every execution of this command returns different results: "[B@40d7c798", "[B@40d848e0", "[B@40d59ff0", & etc.

Purpose: I have an android device with internal printer of receipts. Vendor has provided library (libfile.so) and sample source for developing own software for device. Printing Simple text is OK, but i have a troubles with printing of an Image (logo).

Here is the vendors` tiny documentation.

p.s:I'm newbie in Java.

Answer 1

Try this

   InputStream inputStream = getAssets().open("logo_print.png");

    byte[] buffer = new byte[8192];
    int bytesRead;
    ByteArrayOutputStream output = new ByteArrayOutputStream();
    while ((bytesRead = inputStream.read(buffer)) != -1) {
        output.write(buffer, 0, bytesRead);
    }
    byte file[] = output.toByteArray();

the byte array contains

1B 2A n ml mh converted data 1B 4A 00

1B 2A -- begin the block

n - printing mode
  a) Q110 support 4 kinds of printing modes,as follow：

    n=0x21: 24-point double-density;

    n=0x20: 24-point single-density;

    n=0x01: 8-point double-density;

    n=0x00: 8-point single-density；

  b) NXP only support n=0x21: 24-point double-density;

converted data

1B 4A 00 end the block and execute print (print start)

like wise

byte[0] = 0x1B;
byte[1] = 0x2A;
byte[2] = 0x21; // 24-point double-density;

and so on...

Answer 2

Copy your image into drawable folder. Then follow the steps:

  Drawable drawable= getResources().getDrawable(R.drawable.image);

Type cast into BitmapDrawable,

  Bitmap bitmap = ((BitmapDrawable)drawable).getBitmap();
  ByteArrayOutputStream out = new ByteArrayOutputStream();
  bitmap.compress(Bitmap.CompressFormat.JPEG, 100, out);
  byte[] buffer= stream.toByteArray();

You can also try below code for asset folder image:

  InputStream stream= null;
    try {
        stream = getAssets().open("fileName.extension");
        byte[] fileBytes=new byte[stream.available()];
        stream.read(fileBytes);
        stream.close();
    } catch (IOException e) {
        e.printStackTrace();
    }

Answer 3

This works for any type of file in the asset folder

InputStream is = getAssets().open("image.png");
byte[] fileBytes=new byte[is.available()];
is.read( fileBytes);
is.close();