How do you write code to unpack 12-bit data from a file?

In one line

The rule

12-bit data means each value is 12 bits (not 8 or 16).

You must group every 3 bytes (24 bits) and split them into two 12-bit numbers.

Let's understand it simply

Imagine you have a bag of ladoos, but each ladoo is cut into 12 pieces. The shopkeeper puts the pieces in a box, but the box can only hold 8 pieces in one row (like 8 bits in a byte). So, to get one ladoo, you have to take some pieces from one row and some from the next. Computers store data in bytes (8 bits), but 12-bit data means each number is 12 bits long. So, you have to "unpack" or separate the 12-bit numbers from the 8-bit bytes.

How it works

1. Read the file as bytes (8 bits each).
2. Take 3 bytes at a time (24 bits in total).
3. Join the 3 bytes into one big 24-bit number.
4. Split the 24 bits into two 12-bit numbers.
5. Repeat for the whole file.

Where you see it in real life

• Digital cameras: Some store pixel values as 12-bit numbers for more colours.
• Medical machines: X-ray or ECG machines may use 12-bit sensors.
• Audio files: Some old audio formats use 12-bit samples.
• Microcontrollers: Sensors may send 12-bit values for temperature or pressure.

Why it matters

• You can read special data files from cameras or machines.
• Useful for engineering, electronics, and data science jobs.
• Needed for competitive programming or coding interviews.
• Helps you understand how computers store and read data.

Worked example

Suppose you have a file with these 3 bytes: 0x12, 0x34, 0x56 (hexadecimal numbers).

Given: bytes = [0x12, 0x34, 0x56]
Step 1: Join bytes to 24 bits: 0x12 = 00010010, 0x34 = 00110100, 0x56 = 01010110
Step 2: Combine: 00010010 00110100 01010110
Step 3: First 12 bits: 000100100011 (0x123)
Step 4: Next 12 bits: 010001010110 (0x456)
Step 5: So, unpacked numbers are 0x123 and 0x456

Common mistakes

• Thinking each value is 2 bytes (16 bits) — but 12 bits is 1.5 bytes.
• Not handling the last few bytes if the file size isn't a multiple of 3.
• Forgetting to use bitwise operations (&, |, <<, >>) to split and join bits.

Remember it

Every 3 bytes = 2 numbers (12 bits each). Read, join, split, repeat!