画像のフォーマットを変換する方法
画像を PNG、JPEG、WebP、GIF、BMP などの形式の間で変換します。
问题
ある形式の画像を、特定の用途やプラットフォームのために別の形式にする必要があります。
前提条件
- 画像形式の理解
- 形式の制限に関する知識
ステップ
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1. Understand format capabilities
PNG supports transparency and lossless compression. JPEG does not support transparency and uses lossy compression. WebP supports both transparency and lossy/lossless. GIF supports animation but limited colors (256). Choose the target format based on your needs.
入力need: transparency + small size输出target: WebP -
2. Convert the image
Load the source image and encode it in the target format. For JPEG, set quality (typically 80-90). For PNG, choose compression level. For WebP, choose lossy or lossless. The conversion happens entirely in the browser using the Canvas API or WebAssembly.
入力PNG → WebP (quality 85)输出WebP image -
3. Verify quality and size
Compare the converted image with the original. Check that transparency is preserved if the target supports it. Compare file sizes. If the target format does not support a feature (e.g., JPEG does not support transparency), decide how to handle it (e.g., composite onto white).
入力converted image输出quality verified, size reduced
期待される結果
適切な品質と機能設定で、目的の形式に変換された画像。
よくあるエラー
- Transparency lost converting to JPEG
- JPEG does not support transparency. Use PNG or WebP instead, or composite the image onto a background color before converting.
- Colors changed converting to GIF
- GIF supports only 256 colors. For photos, use PNG or WebP. For simple graphics, GIF may be acceptable.
トラブルシューティング指引
- If quality is poor, increase the quality setting for lossy formats.
- If the file is larger, the target format may be less efficient for this image type.
セキュリティ上の制限
- Image conversion is a local operation. No image data leaves your browser.