ToolBox Image — 画像を正確に100KB（または任意のターゲットサイズ）に圧縮する方法
フォームアップロード、データベース制限、プラットフォーム要件のために100KB未満の画像が必要ですか？ToolBox Imageで任意の正確なサイズを実現する方法をご紹介します。
Need to squeeze an image under 100 KB for a form upload? Hit exactly 250 KB for a job application system? Exact file size compression is one of the most requested features in any image tool.
Why exact file size matters
Most platforms don't just recommend staying under a limit — they hard-reject files that exceed it. A 101 KB file gets blocked by a 100 KB limit just as firmly as a 10 MB file.
How target-size mode works
The compressor takes a different approach than most tools. Instead of asking you to pick a quality number and hoping the file size is acceptable, it works backwards:
- You enter the maximum file size in KB
- The compressor starts at the highest quality setting and compresses the image
- If the result is still above the target, it lowers quality and tries again
- Once the result fits under the target, it runs a fine-tuning pass to maximise quality while staying under the limit
Real example: compressing to 100 KB
Take a 12 MB photo from a modern smartphone. To fit under 100 KB, the compressor needs to reduce the file by a factor of 120 — a 99.2% reduction. The compressor automatically switches to AVIF or WebP based on what produces the best result.
Batch compressing to a fixed size
Target-size mode works with batch processing too. Drop 50 images into the compressor, set the target to 500 KB, and every file comes out under that limit.