Lossy vs lossless compression
What is the difference between lossy and lossless compression? Complete guide to choose the right method for your needs.
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Understanding the difference between lossy and lossless compression is fundamental to properly optimizing your images. Each method has its advantages and specific use cases.
Lossy compression reduces size more by permanently deleting certain data, while lossless compression preserves all original information.
This guide will help you choose the appropriate method based on your needs: web, printing, archiving, or later editing.
Table of contents
What is lossy compression?
Lossy compression analyzes the image and removes information deemed non-essential for human perception.
The JPG format uses this method: it eliminates subtle color variations that the human eye doesn't easily distinguish.
This approach allows for spectacular size reductions (70-90%) but the deleted data is unrecoverable.
What is lossless compression?
Lossless compression reduces file size without deleting any data. The decompressed image is bit-for-bit identical to the original.
PNG and TIFF formats support lossless compression. It's also the principle of ZIP archives.
Reductions are more modest (10-50%) but quality is perfectly preserved.
When to use lossy compression?
For the web: photos and visuals intended for screen display where minimal size is priority.
For social media: platforms recompress your images anyway.
For previews and thumbnails: maximum quality isn't necessary for small images.
When the final file won't be edited again: lossy compression shouldn't be applied to working files.
When to use lossless compression?
For archiving: preserve the original quality of your important photos.
For editing: keep working files in lossless format (TIFF, PNG, PSD).
For logos and graphics: lossy compression artifacts are visible on flat color areas.
For professional printing: maximum quality is necessary for large formats.
Technical comparison
File size: Lossy = 10-30% of original / Lossless = 50-90% of original.
Quality: Lossy = slight degradation / Lossless = identical to original.
Reversibility: Lossy = irreversible / Lossless = perfectly reversible.
Ideal for: Lossy = web photos / Lossless = graphics, logos, archiving.
The hybrid approach
Keep an original version (lossless) and create web-optimized versions (lossy).
Use tools that offer a before/after preview to evaluate quality loss.
WebP format offers both modes: choose lossy for photos, lossless for graphics.
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How to do it in 3 steps
Determine the final use of your image: web, printing, archiving, editing.
Choose the appropriate compression type: lossy for web, lossless for archiving and editing.
Apply compression and check the result. Adjust settings if necessary.
Pro tips
- Keep an original version.
- Test several quality settings.
- Use WebP when possible.
- Choose a descriptive file name.
Common mistakes to avoid
- ✗Applying lossy compression on a working file that you'll need to edit again.
- ✗Using lossless for web photos, resulting in files that are too large.
- ✗Compressing the same file with lossy multiple times, accumulating degradation.
- ✗Choosing PNG (lossless) for photos when JPG or WebP would be more appropriate.
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