How do I transfer RAW file using the bluetooth?

Hi , I'm korean student.
I'm working on my project that tft-LCD display saved-image from SDcard. But, In order to transfer data using the bluetooth
between arduino, I must use "Serial read/write". Is it so? But, "serial read/write" allowed only 1byte and RAW file is 2byte/1pixel.

So, I want to know how to transfer RAW data using the bluetooth and how to save RAW data to SDcard.
Please give me advise.??

void setup()
{

  Serial.begin(9600);
  Serial1.begin(9600); //hardware Serial use. //pin18,19
  // Setup the LCD
  myGLCD.InitLCD();
  myGLCD.setFont(SmallFont);
  myGLCD.fillScr(0, 0, 255);

  

  if(!sd_raw_init())
  {
    Serial.println("MMC/SD initialization failed");      
  }
  pinMode(SD_PIN, OUTPUT);
  if (!SD.begin(SD_PIN)) {
    ShowMessage("SD not ready");
    return;
  }

  delay(10);
  //root = SD.open("/PICTURE");
  //WalkDirectory(root);

  //    ShowMessage("That's the end of the show", "Press RESET to start over");
}

void loop()
{
  datafile= SD.open("log2.txt",FILE_WRITE);

  int i=1;
  if(Serial1.available())
  {
    while(Serial1.available()>0) 
    {
      
           inbyte_char= Serial1.read();
           
            Serial.print(inbyte_char);
            if( (i%50)==0) { //cutting 50 row.

              Serial.println("");
            }
            i++;
           datafile.write(inbyte_char); 
            delay(1);
      }
      
      Serial.println("Read success!");
    }
   datafile.close();
     //Serial.println("Read success!");
  }

between arduino, I must use "Serial read/write". Is it so?

Yes.

But, "serial read/write" allowed only 1byte and RAW file is 2byte/1pixel.

The file contains bytes. It is up to the application that reads the files to know how many bytes to read in any given situation.

Thank you answer.
Then, all data types of RAW file are 'byte'?
For example,
when
char inbyte_char;
inbyte_char = Serial1.read();

Do I need to change the data type 'char' of 'inbyte_char' to the data type 'byte'?
Please help me one more time.

Then, all data types of RAW file are 'byte'?

All files are just bytes.

char inbyte_char;

No. The name needs to be inbyte_char_float_int_double_long_bool.

Do I need to change the data type 'char' of 'inbyte_char' to the data type 'byte'?

Yes.