Glossary · Image compression
What is image compression? Lossy vs lossless explained
Short answer
Image compression is any method that makes a picture file smaller. Lossless compression packs the same pixels more efficiently and can be undone exactly; lossy compression throws away detail people are unlikely to notice. Phone photos are lossy-compressed when the camera saves them, and often again when chat apps, social networks or cloud backups re-process them.
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What is the difference between lossy and lossless?
| Lossless | Lossy | |
|---|---|---|
| What is removed | Only redundancy | Fine detail and some colour |
| Reversible | Yes, pixel for pixel | No |
| Typical formats | PNG, lossless WebP, DNG | JPEG, HEIC, AVIF, lossy WebP |
| Typical use | Screenshots, graphics, editing masters | Camera photos, web images, chat |
Lossless methods look for patterns, such as long runs of the same colour, and store them compactly. That works well for screenshots with flat areas and text, which is why Android saves screenshots as PNG on many phones. Lossy methods transform the image into frequencies and drop the finest ones, which is how a 36 MB worth of raw pixel data becomes a 3 MB JPEG.
Newer lossy formats squeeze harder. HEIC and AVIF use video-codec techniques that predict each block from its neighbours, so they reach similar quality to JPEG at a smaller size. WebP sits between the two and is common on websites and in chat stickers.
Where does your photo get compressed?
- In the camera. The phone encodes the image as JPEG or HEIC at a high quality setting.
- In chat apps. WhatsApp and similar apps resize and re-encode photos to send them quickly, unless you choose an HD or document option.
- On social networks. Uploads are resized and re-encoded again for the web.
- In cloud backup, if you choose it. Google Photos' Storage saver re-compresses photos and resizes those above 16 MP.
Each lossy step compounds the one before it. A picture that has travelled through two groups and a social site can be a fraction of the original's size and visibly softer.
Does compressing your photos free space?
A little, at a cost. Re-saving a 4 MB JPEG at lower quality might bring it to 2 MB, but the lost detail never returns, and you end up judging quality photo by photo. Converting JPEG to HEIC with a good encoder saves more with less visible loss, though compatibility suffers.
Deleting is usually the better lever. A gallery with 5,000 near-copies, received forwards and expired screenshots loses more weight by removing those than by squeezing every keeper. GalleryJury, an AI photo cleaner for Android coming soon to Google Play, takes that route: it picks what to clear and leaves your kept photos untouched, at full quality.
If you do compress, keep a quality setting of 80 or above and test a few photos at full screen before converting a whole folder.
Frequently asked questions
Is PNG better than JPEG for photos?
Not usually. PNG is lossless, so a camera photo saved as PNG is several times larger with no visible gain. PNG suits screenshots and graphics.
Why are screenshots sometimes larger than photos?
Lossless PNG keeps every pixel exactly. A screenshot full of detailed images can be larger than a JPEG photo of a simple scene.
Sources
- Google Photos Help: Choose the upload size of your photos and videos (checked 31 October 2026)
- Android Developers: Supported media formats (checked 31 October 2026)
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