Lossless vs Lossy Compression — What Is the Difference?
When you compress an image, you are choosing between two fundamentally different approaches. Lossless compression keeps every pixel intact — the decompressed image is identical to the original. Lossy compression achieves much smaller files by permanently discarding data that is imperceptible to human vision. Knowing which to use saves storage, load time, and unnecessary quality loss.
Format Reference
| Format | Type | Transparency | Best for |
|---|---|---|---|
| PNG | Lossless | Yes | Logos, icons, screenshots |
| GIF | Lossless (8-bit) | Yes (1-bit) | Simple animations, flat graphics |
| WebP lossless | Lossless | Yes | Logos on web (26% smaller than PNG) |
| JPEG / JPG | Lossy | No | Photographs, complex images |
| WebP lossy | Lossy | Yes | Web photos (30% smaller than JPEG) |
| AVIF | Lossy | Yes | Modern web photos (50% smaller than JPEG) |
| HEIC | Lossy | No | iPhone photos (2× smaller than JPEG) |
What Is Lossless Compression?
Lossless compression reduces file size using mathematical patterns in the data — run-length encoding, Huffman coding, and LZ77/LZ78 algorithms. These find repetition in the pixel data and represent it more efficiently, like a shorthand. When the file is decompressed, the original data is reconstructed exactly.
The key property: you can open and re-save a PNG file a thousand times and the pixel data never changes. This makes lossless essential for source files, design assets, and any image that will be edited further.
The trade-off is file size. A photograph saved as PNG is typically 3–10× larger than the same photo as a JPEG at quality 80 — because photos contain complex pixel variations that lossless algorithms cannot compress efficiently.
What Is Lossy Compression?
Lossy compression permanently removes data from the image. The compression algorithm exploits limits of human vision — the eye is less sensitive to color variation than to brightness variation, and less sensitive to high-frequency detail in uniform areas. JPEG divides images into 8×8px blocks and discards imperceptible detail in each block.
The amount of data removed is controlled by a quality setting (1–100 in most tools). At quality 80, JPEG compression is perceptually lossless for photographic content — the difference is not visible at normal viewing distances. At quality 60, artifacts begin to appear in fine detail and gradients.
The trade-off: each save removes data permanently. Re-saving a JPEG adds another generation of loss. If you need to edit an image repeatedly, keep the source as PNG or a raw camera format and export to JPEG only at the final step.
File Size Comparison
The same 1920×1080 photograph saved in different formats at visually similar quality:
| Format | File size (photo) | vs JPEG |
|---|---|---|
| PNG (lossless) | 3.2 MB | 10× larger |
| JPEG quality 90 | 680 KB | Baseline |
| JPEG quality 80 | 320 KB | 2× smaller |
| WebP lossy (quality 80) | 230 KB | 3× smaller |
| AVIF (quality 80) | 160 KB | 4× smaller |
All lossy entries above are visually indistinguishable from the JPEG quality 90 baseline at normal screen viewing distance. The PNG is identical — and 10× larger.
When to Use Lossless
- Logos and brand assets. Sharp edges, flat colors, and text need lossless — JPEG creates visible blocking artifacts around hard edges. Use PNG.
- UI screenshots and diagrams. Screen captures contain fine text and pixel-perfect lines that look blurry in JPEG. PNG is always better.
- Source files you will edit later. Keep your working files as PNG or in a raw format. Export to JPEG only at the final step.
- Images with transparency. PNG supports alpha channel transparency. JPEG does not — it fills transparent areas with white or black.
- Medical, legal, or archival images. Any context where exact pixel fidelity is required by policy or regulation needs lossless.
When to Use Lossy
- Photographs for web and social media. A photo at JPEG quality 80 is visually identical to the lossless PNG and 10× smaller. Use JPEG or WebP lossy for every photograph displayed on a website.
- Email attachments. Most email providers limit attachments to 20–25 MB. Compressing photos to JPEG quality 80 reduces a typical smartphone photo from 8 MB to under 300 KB.
- Presentation slides. PowerPoint and Google Slides embed images at full resolution. Pre-compressing to JPEG quality 80 can reduce a 50 MB deck to under 5 MB with no visible quality difference on a projector.
- Social media uploads. Platforms like Instagram, LinkedIn, and WhatsApp re-compress images after upload anyway. Uploading JPEG quality 85 as the source gives the platform a clean starting point.
WebP — The Best of Both
WebP supports both lossless and lossy compression in a single format. WebP lossy produces files 25–35% smaller than JPEG at the same visual quality. WebP lossless is 26% smaller than PNG on average. All modern browsers support WebP — Chrome, Firefox, Safari 14+, and Edge.
For new web projects in 2026, WebP lossy is the recommended default for photographs and WebP lossless for logos and graphics. Convert existing images using compressimg.pro/jpg-to-webp or compressimg.pro/png-to-webp.
Related Tools
- Compress image — lossy compression with quality control
- PNG to JPG — convert lossless to lossy for smaller file size
- JPG to PNG — convert lossy to lossless for editing
- JPG to WebP — smaller lossy format for modern browsers
- PNG to WebP — smaller lossless format for modern browsers
Frequently Asked Questions
What is the difference between lossless and lossy compression?
Lossless compression reduces file size without removing any image data — the decompressed file is pixel-for-pixel identical to the original. Lossy compression achieves much smaller files by permanently removing data that is imperceptible to human vision.
Is PNG lossless or lossy?
PNG is always lossless. Every pixel is preserved exactly when a PNG is saved and re-opened, no matter how many times. This makes PNG the correct format for logos, icons, screenshots, and any image where sharp edges or exact colors must be preserved.
Is JPEG lossless or lossy?
JPEG is lossy. Each time a JPEG is saved, the compression algorithm discards some image data permanently. The quality setting (1–100) controls how much data is removed — quality 80–85 is typically indistinguishable from the original at normal viewing distances.
Which is better for photos — lossless or lossy?
For web and social media, lossy (JPEG or WebP lossy) is better for photos. A 2 MB photograph compressed to JPEG quality 80 is typically 150–300 KB with no visible quality difference. Lossless PNG of the same photo would still be 3–5 MB — too large for web performance.
When should I use lossless compression?
Use lossless for: logos and brand assets, UI screenshots and diagrams, medical or legal images, source files you will edit again later, and images with transparent backgrounds.
What is WebP and is it lossless or lossy?
WebP supports both modes. WebP lossy achieves 25–35% smaller files than JPEG at the same visual quality. WebP lossless is 26% smaller than PNG on average. All modern browsers support WebP, making it the best choice for web images in 2026.