When you save an image, you often have to choose between "Quality" and "File Size". This trade-off is governed by the two fundamental types of digital compression: Lossy and Lossless.
Lossy Compression: The Art of Forgetting
Formats: JPG, HEIC, WebP (Lossy mode)
Lossy compression works on the principle that the human eye is imperfect. It looks for minor color changes or subtle details that you probably won't notice and simply deletes them forever.
Think of it like summarizing a book. You might skip a few descriptions of the scenery, but the main plot remains intact. However, if you "summarize the summary" deeply enough (re-saving a JPG multiple times), the story eventually stops making sense. This is called "generation loss".
When to use it:
- Photographs
- Website banners
- Social media posts
Lossless Compression: The Art of Packing
Formats: PNG, GIF, BMP, WebP (Lossless mode)
Lossless compression is more like zipping a folder. It looks for patterns—like a large patch of blue sky—and writes "100 blue pixels here" instead of "blue pixel, blue pixel, blue pixel...".
When you open the file, it unpacks exactly to its original state. Not a single bit of data is lost. The downside? The file sizes are significantly larger because it can't "cheat" by deleting complex details.
When to use it:
- Logos and Icons
- Screenshots with text
- Professional archival
- Images that need transparency
Which one should you choose?
For most users, Lossy is the right choice for sharing photos. The space savings (often 90%!) are worth the imperceptible drop in quality. But for designers or business owners, keeping a Lossless master copy is essential.