Lossy vs Lossless Compression
Also known as: lossy vs lossless, compression types
Lossy compression permanently discards image or video data the eye is least likely to notice, shrinking files dramatically. Lossless compression repacks data so the original is perfectly reconstructable, saving far less space. Camera-roll formats like JPEG, HEIC, and H.264 are lossy, which is why deleting them, not re-compressing them, frees the most storage.
- Lossy formats (JPEG, HEIC, H.264) discard data permanently to achieve much smaller files than lossless formats.
- Lossless compression rebuilds the original exactly but typically saves far less space.
- Re-compressing already-lossy camera-roll files frees little space and can cause cumulative quality loss.
How each type works
Lossy compression throws away information the human visual system is poor at detecting, such as subtle color shifts and high-frequency detail. The result cannot be turned back into the exact original, but the file becomes a fraction of its uncompressed size. JPEG, HEIC, and video codecs like H.264 and HEVC are all lossy, which is what makes photos and videos small enough to store thousands on a phone.
Lossless compression works more like a ZIP file: it finds and removes statistical redundancy so the original bytes can be rebuilt bit-for-bit. Formats such as PNG, FLAC, and most RAW files are lossless or near-lossless. Because nothing is discarded, the space saved is modest compared to lossy methods.
Why it matters for your camera roll
Almost every photo and video on a phone is already lossy and already compressed near its practical limit. Trying to re-compress them again yields little extra space and can visibly degrade quality with each pass, a problem known as generation loss.
Because the files are already small for what they contain, the biggest storage wins come from removing whole files: duplicates, near-identical burst frames, screenshots, and large videos. A cleaner like Cleanor targets those redundant files rather than re-compressing data that is already efficiently packed.