When you save an image, audio file, or video, the software makes a choice: store everything with perfect accuracy, or throw away some data to make the file smaller. This is the lossless vs lossy trade-off — and it has permanent consequences for your files.
What lossless compression does
Lossless compression encodes data so it can be reconstructed perfectly. No information is discarded. When you decompress a lossless file, you get exactly the same data that went in — bit for bit.
Think of it like a zip archive. Zipping a folder makes it smaller; unzipping it gives you the exact original files.
Lossless formats: - Images: PNG, BMP, TIFF, WebP (lossless mode) - Audio: WAV, FLAC, AIFF - Archives: ZIP, TAR, 7z (when compressing already-compressed content, gains are small) - Documents: DOCX, XLSX, ODS (internally zip-compressed XML)
What lossy compression does
Lossy compression achieves smaller files by permanently discarding data the human senses are unlikely to notice. The result looks (or sounds) similar to the original, but it is not identical. The discarded data is gone — you cannot recover it.
Lossy formats: - Images: JPEG, HEIC, WebP (lossy mode) - Audio: MP3, AAC, OGG, Opus - Video: MP4 (H.264/H.265), WebM, AVI (with lossy codec)
Why this matters for conversions
This is where the practical consequences kick in. There are four types of conversions:
| Conversion type | Quality result | Example |
|---|---|---|
| Lossless → lossless | No loss | PNG → BMP |
| Lossless → lossy | Quality reduced once | PNG → JPEG |
| Lossy → lossless | Artifacts preserved, larger file | MP3 → WAV |
| Lossy → lossy | Quality reduced again | JPEG → JPEG (re-save) |
The critical one to understand: lossy → lossless does not restore quality.
If you convert an MP3 to WAV, you get a large WAV file — but the audio information lost when the MP3 was encoded is gone permanently. The WAV isn't higher quality than the MP3. It's the same audio in a bigger container.
Similarly, if you open a JPEG in Photoshop and save it as PNG, you get a lossless PNG — but the visual data discarded when the JPEG was first created is not magically restored.
Generation loss: re-saving lossy files
Each time you open and re-save a lossy file, you lose quality again. This is called generation loss or transcoding loss.
A JPEG saved at quality 90% → re-saved at 90% → re-saved at 90% will visibly degrade over generations. You'll see blocking artifacts, smeared edges, and color banding that weren't in the original.
The rule: always keep a master copy in a lossless format. Convert to lossy only as the final delivery step, and only when needed.
How much quality does lossy actually lose?
It depends on the compression setting (often called "quality" or "bitrate"):
Images — JPEG quality: - 90–100%: Nearly indistinguishable from lossless. Large file. - 70–85%: Excellent for web use. Small, looks great on screen. - Below 50%: Visible blocking and smearing. Only useful for thumbnails.
Audio — MP3 bitrate: - 320 kbps: Transparent — most listeners can't distinguish from lossless. - 192 kbps: Very good. Standard for streaming. - 128 kbps: Acceptable. Audible artifacts on some content (cymbals, reverb). - Below 128 kbps: Clearly degraded.
Which conversions are safe on Converthor
| Converter | Type | Notes |
|---|---|---|
| PNG to JPG | Lossless → lossy | Quality reduced once, fine for web |
| JPG to PNG | Lossy → lossless | Larger file, artifacts preserved |
| WAV to MP3 | Lossless → lossy | Quality reduced once, fine for distribution |
| MP3 to WAV | Lossy → lossless | No quality gain, just format change |
| FLAC to MP3 | Lossless → lossy | Recommended path for distribution |
| PNG to WebP | Lossless → lossy | 25% smaller, good visual quality |
The practical workflow
- Record or create in lossless — WAV for audio, PNG for graphics, RAW for photos
- Edit in lossless — keep your master file untouched
- Export as lossy for delivery — MP3 at 192+ kbps, JPEG at 80–85%, WebP for web images
- Never re-export from the lossy file — always go back to the master
Following this workflow, lossy compression is a tool, not a problem. The quality loss is controlled, predictable, and happens exactly once.