How to convert 2 byte data to integer?

I have a two byte data (unsigned) as array.

e.g. x=[255 67]

I read the data from a sensor giving a stream of byte data (unsigned 0 to 255). From them I select corresponding two-byte of data set for necessary parameter calculation.

I want to convert this into an Integer value or a double value to do real mathematic calculations.

I tried with.

x=uint8([1 0]) y=typecast(x,'uint32') % but this gives an error.

if I use: x=uint16([255 67]) y=typecast(x,'uint32')

% answer is

4391167

I don't how to check the answer is correct or not. Or the conversion syntax is correct?

Can anyone give me the code for correct 2-byte data conversion to integer..!

Answer 1

[Guillaume]

You were nearly there. combining two bytes (uint8) does not make a 32-bit number (uint32), but a 16-bit numbers (uint16), so:

x = [255 67];
y = typecast(uint8(x), 'uint16');

You haven't specified the endianness of your data, nor that of your machine. If the two don't match, you'll have to swapbytes afterward:

truey = swapbytes(y); %if one is big-endian and the other litte-endian

[Tharindu Weerakoon]

Hi Guillaume,

Actually I have the byte array in my C# program like: (simply, not the real commands) byte[] x; x={20, 0, 1, 255, 178, 0, 35, 255, 138}

Y1: convert the byte value 20 (lower byte from right side) to integer (int in C#) and answer should equal to 20.

Y2: two byte array [0 1] (1: lower byte) should be converted to int16 and then the answer should be equal to 1

Y3: for the two byte array [255 178] (lower byte is 178)should be converted to the int16 and then the answer divided by 32767.0f/360.0f in C# should give the answer looks like -0.93387.

Y4: for the two byte array [0 35] (lower byte is 35) should be converted to the int16 and then dividing by 32767.0f/360.0f should give the answer looks like 0.56032

Y5: for the two byte array [255 138] (lower byte is 138) should be converted to int16 and then it is divided by 32767.0f/3.0f should give the answer looks like -0.01053.

For your reference I have put my C# code here to get more clear understanding about my problem.

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="X"></param>
      public DataConversion(byte[] X)
        {

            //Decoding
            int index = 0;
            Y1= (int)X[index++];            
            Y2 = (Decode2byte(X[index++], X[index++]) == 1);

            double bias = 0;         

            bias = 32767.0f / 360.0f;
            Y3 = Decode2byte(X[index++], X[index++]) / bias;
            Y4 = Decode2byte(X[index++], X[index++]) / bias; 

            bias = 32767.0f / 3.0f;
            Y5= Decode2byte(X[index++], X[index++]) / bias;

        }

        /// <summary>
        /// Two byte data conversion to int16
        /// </summary>
        /// <param name="data1"></param>
        /// <param name="data2"></param>
        /// <returns></returns>
        private Int16 Decode2byte(byte data1, byte data2)
        {
            return (Int16)(data1 << 8 | data2);
        }

Could you please tell me how can I do this in matlab

Answer 2

[Image Analyst]

I don't know which element of x is the upper or lower byte, so I did it both ways. Try this:

x=[255 67]
% Display bytes in binary.
dec2bin(x(1))
dec2bin(x(2))
% If x(1) is the most significant byte:
x_uint16 = uint16(256*x(1) + x(2))
dec2bin(x_uint16)
% If x(1) is the least significant byte:
x_uint16 = uint16(256*x(2) + x(1))
dec2bin(x_uint16)

Note that x must be a double or a uint16 variable, not a char or uint8 variable or else you can't multiply by 256.

In the command window, you'll see:

x =
 255    67
ans =
11111111
ans =
1000011
x_uint16 =
65347
ans =
1111111101000011
x_uint16 =
17407
ans =
100001111111111

You can replace uint16 by double if you want the data type to be double instead of uint16.

[Tharindu Weerakoon]

Hi,

Actually I get the data as unsigned byte data (uint8) (0 to 255 ) and I want then to convert into signed int16 (-2^15 to 2^15-1)data.

I have the byte array in my C# program like: (simply, not the real commands) byte[] x; x={20, 0, 1, 255, 178, 0, 35, 255, 138}

Y1: convert the byte value 20 (lower byte from right side) to integer (int in C#) and answer should equal to 20.

Y2: two byte array [0 1] (1: lower byte) should be converted to int16 and then the answer should be equal to 1

Y3: for the two byte array [255 178] (lower byte is 178)should be converted to the int16 and then the answer divided by 32767.0f/360.0f in C# should give the answer looks like -0.93387.

Y4: for the two byte array [0 35] (lower byte is 35) should be converted to the int16 and then dividing by 32767.0f/360.0f should give the answer looks like 0.56032

Y5: for the two byte array [255 138] (lower byte is 138) should be converted to int16 and then it is divided by 32767.0f/3.0f should give the answer looks like -0.01053.

For your reference I have put my C# code here to get more clear understanding about my problem.

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="X"></param>
      public DataConversion(byte[] X)
        {

            //Decoding
            int index = 0;
            Y1= (int)X[index++];            
            Y2 = (Decode2byte(X[index++], X[index++]) == 1);

            double bias = 0;         

            bias = 32767.0f / 360.0f;
            Y3 = Decode2byte(X[index++], X[index++]) / bias;
            Y4 = Decode2byte(X[index++], X[index++]) / bias; 

            bias = 32767.0f / 3.0f;
            Y5= Decode2byte(X[index++], X[index++]) / bias;

        }

        /// <summary>
        /// Two byte data conversion to int16
        /// </summary>
        /// <param name="data1"></param>
        /// <param name="data2"></param>
        /// <returns></returns>
        private Int16 Decode2byte(byte data1, byte data2)
        {
            return (Int16)(data1 << 8 | data2);
        }

Could you please tell me how can I do this in matlab

Answer 3

[Tharindu Weerakoon]

Hello everyone,

Thanks a lot for the help. Finally I could do it.

% Two byte array [lower bit , higher bit] x=uint8[178 255]

% convert to signed int16 y=typecast(x,'int16')

% if want to use this for other mathematical calculations, it should be converted to the double. z=double(y)

% simple math operation. int16 range value is -32768 ~32767 Out=(z/32767)*250

Result will be x = 178 255

y = -78

z = -78

out = -0.595110934781945

Thanks again all

[mohd akmal masud]

hi all,

i have image dicom 16 bit. Like below my image:

>>P=dicomread('PET_I1001_PT135.dcm');

>> whos P

Name        Size              Bytes  Class    Attributes

P         256x256            131072  int16

My problem is, 16 bit image can stored pixel value till 32767 only. Now i want change it to 32 bit or 64 bit so that the pixel value can stored more than that, and corresponding how much activity radionuclides i used to diagnosed patient.

can you help to convert that using matlab? or anyway to solve it?