オンラインでJPEGファイルサイズを縮小

Reduce JPEG File Size Online SELECT FILES CLEAR Drop Your Files Here COMPRESS 0 SAVE ALL 0 Before: 0 KB After: 0 KB (-0%) 100% Quality APPLY JPEG Compression: Complete Guide JPEG compression reduces file sizes by removing image data that the human eye typically doesn't notice. Our tool uses MozJPEG, an advanced encoder developed by Mozilla that achieves better compression ratios than standard JPEG encoders while maintaining excellent visual quality. Key Fact: A typical high-resolution photo can be compressed by 60-80% without visible quality loss. This means faster page loads, easier sharing, and significant storage savings. Why Compress JPEG Images? Large image files create real problems across many use cases: Website Performance Images typically account for 50-70% of a webpage's total size. Unoptimized photos slow down page load times, hurt SEO rankings, and increase bounce rates. Google explicitly uses page speed as a ranking factor. Storage and Bandwidth Whether you're storing photos in the cloud, on your device, or hosting them on a server, smaller files mean lower costs and more capacity. Email services and messaging apps often have strict size limits that uncompressed photos exceed. Faster Sharing Compressed images upload and download faster, making sharing smoother on any connection—especially important for mobile users on limited data plans. Pro Tip: For web use, aim for images under 200KB. Most photos can reach this size at quality 75-85 without visible degradation. How JPEG Compression Works JPEG uses lossy compression, which means some image data is permanently removed to achieve smaller files. The compression process: Converts colors to a format where brightness and color information are separated Divides the image into 8×8 pixel blocks Applies mathematical transforms to identify less important visual information Removes data based on the quality setting you choose MozJPEG improves on standard JPEG encoding by using smarter algorithms to decide what data to remove, achieving 5-15% better compression at the same visual quality. Important: Each time you save a JPEG, it's compressed again. Avoid repeatedly editing and saving the same JPEG—work with the original or use a lossless format for editing. Choosing the Right Quality Level Quality Best For Typical Reduction 90-100 Archiving, professional photography 20-40% 75-89 Web images, social media, email 50-70% 60-74 Thumbnails, previews 70-85% Below 60 Maximum compression when quality is secondary 85%+ How to Use This Tool Add files — Click SELECT FILES or drag up to 20 JPEGs into the drop area Compress — Click COMPRESS to process all files with optimal settings Fine-tune (optional) — Click any thumbnail to manually adjust quality with the slider Save — Save individual files or use SAVE ALL Typical Results Smartphone photo (4MB): Compressed to ~400KB at quality 80 — 90% reduction DSLR image (12MB): Compressed to ~800KB at quality 85 — 93% reduction Screenshot with photos (2MB): Compressed to ~300KB at quality 75 — 85% reduction Privacy and Security Your images never leave your device. All compression happens locally in your browser using WebAssembly technology: No server uploads — processing is 100% client-side No data collection — we cannot see your images No registration — just open and use Original files preserved — only the downloads are compressed Terms and Privacy