Convertisseur d'Images

PNG (Portable Network Graphics) uses lossless DEFLATE compression, preserving every pixel exactly. It supports transparency (alpha channel) and is ideal for graphics with sharp edges: logos, icons, screenshots, and UI elements. PNG files are typically larger than JPEG for photographs because lossless compression can't exploit the smooth gradients in photos. PNG supports 8-bit (256 colors) and 24-bit (16.7 million colors) modes, plus 32-bit (24-bit + alpha).

JPEG (Joint Photographic Experts Group) uses lossy discrete cosine transform (DCT) compression, achieving 10:1 to 20:1 compression with minimal visible quality loss. It's designed for photographs and natural images with smooth gradients. JPEG doesn't support transparency and introduces compression artifacts (blocky patterns) at high compression ratios. The quality parameter (typically 70-95) controls the trade-off between file size and visual quality. JPEG is the most widely supported image format on the web.

WebP is Google's modern format that combines the best of PNG and JPEG: it supports both lossy and lossless compression, transparency, and animation. WebP files are typically 25-35% smaller than equivalent JPEGs and PNGs. It's supported by all modern browsers (Chrome, Firefox, Safari, Edge). Converting from PNG/JPEG to WebP can significantly reduce page load times. However, some older image editing software doesn't support WebP, so keeping the original is recommended.

Browser-based image conversion uses the Canvas API as an intermediary. The source image is loaded into an Image object, drawn onto a canvas element, then exported in the target format using canvas.toBlob() or canvas.toDataURL() with the desired MIME type and quality. This works for any format the browser can decode (PNG, JPEG, WebP, GIF, BMP, ICO) and any format it can encode (PNG, JPEG, WebP).

A limitation of canvas-based conversion is that it decodes the image into raw pixels (RGBA) and re-encodes it. This means converting from one lossy format to another (e.g., JPEG to WebP) applies compression twice, potentially degrading quality. For best results, convert from a lossless source (PNG) or use the highest quality setting. Also, EXIF metadata (camera settings, GPS location, timestamp) is typically lost during canvas conversion because the canvas only stores pixel data. Use the exif-editor tool if you need to preserve or modify EXIF data.