Does this upload my photos?

No. Re-encoding uses the canvas API in this tab. Close the page to drop the pixels from memory.

Why is the result always JPEG?

JPEG quality is the reliable browser knob for “make this smaller.” PNG stays lossless unless you re-encode; this tool converts to JPEG so quality/target-size controls actually shrink the file.

Target size vs quality slider?

Quality is a 10–95% JPEG factor. An optional target in KB binary-searches quality until the blob is under that size (or the minimum quality is reached). Huge photos may still miss a tiny target.

Will faces and text stay sharp?

Heavy compression adds block artifacts, especially on text and UI screenshots. Prefer PNG/WebP sources at a higher quality, or crop before compressing.

Utill.net

画像圧縮

JPEG品質・目標サイズ

JPEG・PNG・WebPの容量をブラウザで削減します。

この変換はブラウザ内だけで実行され、サーバーへはアップロードされません。

画像をドラッグ＆ドロップ、または下から選択

ファイルを参照

JPEG 品質: 75%

目標サイズ（KB、任意）

このツールについて

A local image compressor. You pick JPEG quality and optionally a maximum size in kilobytes. The browser draws the image on a canvas and exports JPEG. Nothing is uploaded.

It does not convert HEIC (use HEIC to JPG first) and does not produce Base64 strings.

よくある用途

Fit a photo under an email or form upload cap (for example 300–500 KB)
Shrink a PNG screenshot that is mostly photographic content
Batch a few web-hero images without opening desktop software

使い方

Drop a JPEG, PNG, WebP, or GIF (GIF becomes a still JPEG).
Set quality. Optionally enter a target size in KB.
Check the before/after sizes, then Download JPG.

例

Input	Notes
4 MB phone JPEG, quality 75%	Typical web-share size drop with moderate artifacts.
PNG screenshot, target 400 KB	May still look blocky; screenshots compress poorly as JPEG.
Already-tiny 80 KB JPEG, quality 90%	Result can be larger — JPEG re-encode is not always smaller.
15 MB+ image	Rejected; downscale in Photos first.

実務での落とし穴

Screenshots: UI chrome and text suffer as JPEG. This tool is aimed at photos.
Transparency: alpha PNG becomes an opaque JPEG (usually black or white-filled by the canvas).
Target size is best-effort; it cannot invent a 50 KB file from a 12 MP RAW-like JPEG without wrecking it.

参考資料

最終更新: 2026-08-30

よくある質問

Does this upload my photos?: No. Re-encoding uses the canvas API in this tab. Close the page to drop the pixels from memory.
Why is the result always JPEG?: JPEG quality is the reliable browser knob for “make this smaller.” PNG stays lossless unless you re-encode; this tool converts to JPEG so quality/target-size controls actually shrink the file.
Target size vs quality slider?: Quality is a 10–95% JPEG factor. An optional target in KB binary-searches quality until the blob is under that size (or the minimum quality is reached). Huge photos may still miss a tiny target.
Will faces and text stay sharp?: Heavy compression adds block artifacts, especially on text and UI screenshots. Prefer PNG/WebP sources at a higher quality, or crop before compressing.