How does compression reduce file size?

In one line

The rule

Compression is the process of encoding information using fewer bits than the original representation, by removing redundancy or unnecessary data.

There is no single formula, but for video: Bitrate = File Size / Duration

Let's understand it simply

Imagine you are packing clothes for a trip. If you just throw them in, your bag fills up quickly. But if you fold them neatly and remove things you don't need, you can fit more in the same bag. Compression works the same way for files. It finds repeated or unneeded parts and packs the important information tightly. This makes the file smaller, just like a neatly packed bag.

How it works

1. The computer looks for repeated patterns or data in the file (like the same colour in many pixels, or the same sound).
2. It replaces these repeats with a shorter code or symbol (like writing '5x blue' instead of 'blue, blue, blue, blue, blue').
3. It removes information that is not needed or that people cannot notice (like tiny colour changes in a video, or very soft sounds in music).
4. It saves the new, shorter version as the compressed file.
5. When you open the file, the computer puts the repeats back, so you see or hear the full thing.

The story behind it

Compression became important as computers and the internet grew. In the 1980s and 1990s, people wanted to send pictures, music, and videos quickly, but internet speeds were slow. Scientists and engineers created smart ways to shrink files, like JPEG for images and MP3 for music. One fun fact: the JPEG image format is named after the group that made it, the Joint Photographic Experts Group.

Where you see it in real life

• Sending photos on WhatsApp → The app compresses your photo so it sends faster and uses less data.
• Watching YouTube videos → Videos are compressed so they load quickly, even with slow internet.
• Listening to songs in MP3 format → MP3 compresses music so you can store thousands of songs on your phone.
• Downloading apps or games → The files are compressed so they take less space and download faster.
• Scanning documents as PDF → The scanner compresses the images inside the PDF so the file is smaller.

Why it matters

• Saves storage space on your phone, computer, or pen drive.
• Makes files faster to send and receive, even on slow networks.
• Reduces data costs, which is important if you have limited internet.
• Lets you store more songs, videos, or photos in the same space.

Common mistakes

• Thinking compression always keeps perfect quality. Some types (like JPEG, MP3) remove small details to save space.
• Believing all files can be compressed a lot. Some files (like already compressed ZIP files) cannot shrink much more.
• Forgetting that too much compression can make pictures blurry or music sound strange.

Remember it

Compression is like folding clothes to fit more in your bag — it packs data tightly by removing repeats and extras.