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Beginner Topic 5 of 49 Graphics, Vision & Media

Image Compression

Reducing image size with lossless or lossy methods.

How it works

Image compression reduces file size. Lossless methods, such as PNG's DEFLATE and lossless WebP, remove redundancy so that the original can be reconstructed exactly. Lossy methods, such as JPEG, discard information the eye is less sensitive to: JPEG converts to a luminance-chrominance space, subsamples chroma, applies a discrete cosine transform to 8 by 8 blocks, quantizes the coefficients and entropy codes them with Huffman coding. Newer codecs use larger transforms, prediction and better entropy coding, as in AVIF and JPEG XL.

Where it is used

Websites, cameras, messaging apps, medical archives and mapping services rely on compression to save storage and bandwidth.

Common pitfall

High compression causes visible artifacts: blockiness, ringing around edges and color banding. Repeated lossy re-encoding accumulates damage. Quality settings are not comparable between codecs. Medical and scientific images may require lossless storage. Choose quality by viewing results, compress once from the original and use responsive images and modern formats for the web.

Where it fits in the course

Image Compression is topic 5 of 49 in Graphics, Vision & Media, rated Beginner. It follows Image Formats. The next topic is Audio Basics.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Graphics, Vision & Media quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Image Compression?
Reducing image size with lossless or lossy methods. It belongs to Graphics, Vision & Media and is a beginner-level topic.
Where do people use Image Compression?
Websites, cameras, messaging apps, medical archives and mapping services rely on compression to save storage and bandwidth.
What is the most common mistake with Image Compression?
High compression causes visible artifacts: blockiness, ringing around edges and color banding.
What should I learn before this topic?
Start with Image Formats, the topic just before it in Graphics, Vision & Media.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Graphics, Vision & Media quiz.
Is Image Compression hard to learn?
It is a Beginner topic, so it works as an entry point. If the terms are new, read the explanation twice and try the visualizer before the quiz.
How long does it take to learn Image Compression?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Image Compression?
Image Formats, Audio Basics, Raster vs Vector Graphics are closely connected. The full list is in the related topics section of this page.
What should I study after Image Compression?
Continue with Audio Basics, the next topic in Graphics, Vision & Media.

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