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無料PNG画像サイズ変更

PNGファイルのサイズが大きすぎてお困りですか？ソフトをインストールせずにオンラインでPNGをリサイズしたい場合も、無料でサイズ変更したい場合も、Image Resizer AIなら数秒で完了します。ファイルをアップロードし、希望の寸法を入力してダウンロードするだけ。簡単です。

ウェブサイト、プレゼンテーション、またはアプリのアイコン用にPNGファイルを調整する必要がありますか？問題ありません。ImageResizerAIは、ブラウザから直接PNGをリサイズできる最適なツールです。会員登録なし、ウォーターマークなし。あなたの画像を指定のサイズに変更します。

Fact: PNG uses lossless compression, which preserves every pixel of the original image. That makes it ideal for graphics, logos, screenshots, and images that require transparent backgrounds.

When Should You Resize a PNG Image?

Resizing a PNG is useful in many situations. Developers often need smaller PNG icons for mobile apps, designers resize transparent logos for websites, ecommerce sellers adjust product badges, and students optimize screenshots before uploading assignments. Smaller PNG files also load faster on websites, improving page speed and creating a better experience for visitors.

PNG vs JPG vs WebP – Which Format Should You Choose?

Feature PNG JPG WebP
Transparency Support ✅ Yes ❌ No ✅ Yes
Best For Logos, screenshots, graphics Photos Modern websites
Compression Type Lossless Lossy Lossy & Lossless
Typical File Size Larger Smaller Usually the smallest
Best Choice When Image quality matters most Sharing photographs Improving website performance

Need More Than Just PNG Resizing?

If you are working with multiple image formats, Image Resizer AI offers dedicated tools for every common workflow. You can resize JPG images online without losing quality, change JPEG image dimensions online, or resize WebP images for websites and blogs. Have dozens of photos to resize at once? Try our bulk image resizer for multiple images. If your goal is meeting a specific upload requirement instead of changing dimensions, our resize image to exact KB size tool is often the better option. You can also explore every browser-based editing tool from the Image Resizer AI homepage.

Frequently Asked Questions

はい、必要な寸法を自由に入力できます。アプリ用の512×512や、Instagram用の1080×1080、その他カスタムの寸法など、数値を入力するだけで完了します。
はい、100%無料でご利用いただけます。アカウント作成やメールアドレス登録、支払いは不要です。PNGをアップロードし、サイズを指定してダウンロードするだけです。
画像を縮小する場合は、画質は鮮明なまま保たれます。元サイズより大きく拡大する場合は、画像がぼやける可能性があります。目安として元の2倍以上の拡大は避けてください。
透過状態は完全に維持されます。透過対応はPNG形式の最大の利点の一つであり、サイズ変更によって透過背景が損なわれることはありません。
完全に安全です。画像はご使用のブラウザ内でローカルに処理され、サーバーに送信されることはありません。第三者に見られることも、保存されることもありません。
Yes. PNG supports an alpha channel, which stores transparency information separately from the visible image. As long as you save the resized image in PNG format, transparent backgrounds, soft shadows, and smooth edges remain intact. Transparency is only lost if you convert the image to a format such as JPG, which does not support transparent backgrounds.
The best dimensions depend on where the image will be used. Website graphics should usually match the actual display size instead of being much larger. App icons often have fixed size requirements, while email signatures and blog graphics typically need relatively small dimensions. A practical rule is to resize the image as close as possible to its final display size. Using oversized images increases page load times and wastes storage without improving visual quality.
Yes. If you have many PNG files that require the same dimensions, using a batch resizing tool is much faster than processing them individually. This approach is particularly useful for ecommerce product images, website assets, presentations, and documentation because every image can be resized consistently in a single workflow.
Screenshots usually contain sharp text, interface elements, icons, and solid colours. JPG compression is designed for photographs and often introduces visible compression artifacts around text and straight lines. PNG stores these details without quality loss, which is why screenshots, diagrams, and software interfaces remain much clearer when saved as PNG. If file size is a concern, resizing the PNG is generally a better solution than converting it to JPG.
It depends on the upload requirements. If the platform specifies exact image dimensions, resize the PNG to those dimensions first. If the platform only limits the maximum file size—for example, under 200 KB—using a tool that reduces an image to a specific KB size is usually the better option. In many situations, resizing the image first significantly lowers the file size, and any additional optimization needed to reach the required KB limit becomes much easier.