Compress Images
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How OnlyFiles compresses images
OnlyFiles uses Sharp, a high-speed image processing library built on industry-standard encoding tools, to compress your images intelligently. For JPG files, Sharp adjusts the JPEG quality setting and re-encodes the image — you get the same visual appearance at a smaller file size. For PNG images, the tool applies both lossless compression (optimizing color palettes and metadata) and optional lossy optimization (reducing color depth) depending on your chosen level. WebP, GIF, and BMP formats each have their own optimization paths. The key difference from simple "export at lower quality" is that Sharp analyzes your image and applies format-specific compression techniques that preserve visual quality while aggressively reducing bytes.
The three compression levels explained
Light compression reduces file size by 10–25% with virtually no visible quality loss — best for images where detail matters, like product photos, artwork, or photos you'll print or display on high-resolution screens. The original image dimensions and color depth stay the same. Balanced compression cuts file size by 30–50% while maintaining good visual quality — ideal for web graphics, email images, and general-purpose use where a slight quality reduction is acceptable. Strong compression prioritizes file size reduction (often 50–70% smaller) with more noticeable quality reduction — perfect for thumbnail images, social media posts, or when bandwidth or storage is severely limited.
What's preserved and what changes
Your image's dimensions, aspect ratio, and color space stay exactly the same — a 1200×800 PNG stays 1200×800. What changes is how efficiently the image data is encoded. For lossy formats like JPG, compression reduces subtle color gradations and fine details. For lossless formats like PNG, compression optimizes the internal color palette and removes redundant pixel data without changing what you see. EXIF metadata (camera settings, GPS location, timestamps) can optionally be stripped during compression to further reduce file size — useful for privacy. The image remains in its original format: PNG stays PNG, JPG stays JPG, and so on.
Choosing the right compression level for your needs
Use Light compression for images destined for print, design portfolios, or high-end web displays where image quality is critical. Light also works well when you're only slightly over a size limit and don't want any visible degradation. Balanced is the go-to choice for most users — it shrinks files significantly without obvious quality loss, making it ideal for website backgrounds, email attachments, and cloud uploads. Choose Strong compression when file size is the priority: sending dozens of images via email, filling up a shared drive with thumbnails, or optimizing for users on slow mobile connections. Strong compression can sometimes produce artifacts or banding in photos with smooth gradients, so preview the result if quality is a concern.
When to use this
- Shrink photos for faster website loading
- Reduce image size for email or messaging without changing format
- Optimize product photos for an online store
Frequently asked questions
Does image compression change the file format?
No. OnlyFiles compression is format-preserving. A PNG stays PNG, a JPG stays JPG, a WebP stays WebP. Only the file size changes — the format and dimensions remain the same.
What image formats can I compress?
OnlyFiles supports compressing JPG, PNG, WebP, GIF, BMP, and HEIC images. Each format is compressed using the optimal algorithm for that format.
How much can I reduce the file size?
It depends on the image and compression level. Photos typically compress 30-70%. Already-optimized images may not compress much further — in that case, OnlyFiles returns your original file instead of a larger one.