PNG vs JPG: Complete Comparison Guide

PNG uses the DEFLATE lossless compression algorithm, which encodes image data in a way that allows exact reconstruction of the original pixel values - every red, green, and blue channel value is preserved byte for byte. This makes PNG the only viable choice for archival purposes, professional design workflows, and any use case where images will be edited and re-saved repeatedly.

JPG uses the Discrete Cosine Transform (DCT) algorithm, which divides the image into 8×8 pixel blocks, converts them to frequency information, and then discards high-frequency components that the human visual system is least sensitive to. The result is dramatically smaller file sizes at the cost of permanent, irreversible data loss - each time a JPG is saved, a new round of lossy compression is applied, progressively degrading quality in a process called generation loss.

For photographs with millions of subtly varying colours and smooth gradients, this lossy process is largely invisible at quality settings of 80-95%, making JPG the dominant format for photographic web delivery. For images with sharp edges, solid blocks of colour, or text overlaid on graphics, JPG compression introduces visible ringing and blocking artefacts that make PNG the clear choice. The quality difference is most visible when zooming in on fine details: PNG preserves every edge pixel perfectly, while JPG smears them into the surrounding colour values. In a professional photo-editing workflow, source images should always be stored as lossless files (PNG, TIFF, or RAW) and exported as JPG only for the final deliverable, never re-opened and re-saved as JPG.

Concrètement, cela signifie que PNG est le seul choix sûr pour tout flux de travail impliquant des cycles répétés d'édition et d'enregistrement, comme l'itération de design, la production d'actifs de marque et le traitement de documents. Les professionnels conservent souvent les fichiers sources en PNG et exportent les livrables finaux en JPG pour bénéficier du meilleur des deux mondes : édition sans perte et diffusion efficace. Pour votre prochain projet, explorez notre PNG vers JPG pour produire des livrables optimisés à partir de sources sans perte.

File size is one of the most significant practical differences between PNG and JPG and is responsible for most real-world format-choice decisions. JPG files are typically 60-90% smaller than equivalent PNG files for photographic content - a full-HD photograph (1920×1080 pixels) might be 4-6 MB as a raw PNG but compress to just 300-600 KB as a JPG at quality 85%, a reduction of more than 90% with minimal perceptible quality loss.

This difference is so dramatic that it essentially dictates JPG for all photographic web content where page load speed and bandwidth costs matter. However, the advantage narrows or reverses for non-photographic content: a 512×512 pixel logo with a white background and sharp text might be 45 KB as a PNG but 90 KB as a JPG because JPG's block-based compression algorithm performs poorly on large uniform regions and creates visible artefacts around sharp colour boundaries.

For web developers, the rule of thumb is straightforward: measure both formats for every asset and choose the smaller one, because the theoretical advantage of one format over the other depends entirely on the specific image content. PNG files can be further reduced by 30-70% using lossless PNG optimisation tools such as our free PNG compressor, which applies more aggressive DEFLATE strategies without any quality loss. JPG files can similarly be re-compressed using our JPG compressor to find the optimal quality setting for a given target file size.

Concrètement, une photographie plein écran (1920×1080 px) peut peser de 4 à 6 Mo en PNG non compressée, mais se compresser à seulement 300-600 Ko en JPG de haute qualité : une réduction supérieure à 90% avec une différence à peine perceptible. Pour une icône d'interface ou un logo en 256×256 px, l'écart se resserre nettement : la compression sans perte de PNG peut produire un fichier plus petit que JPG, car les grandes zones de couleur unie et les bords nets se compressent avec une efficacité extrême en algorithme sans perte. Conclusion : testez toujours les deux formats pour vos ressources spécifiques. Utilisez notre compresseur PNG et notre compresseur JPG côte à côte pour mesurer les économies réelles pour votre contenu.

Loading speed is directly tied to file size - smaller files download faster, which is why JPG typically loads faster than PNG for photographic content. On a typical 4G mobile connection (approximately 20 Mbps download), a 500 KB JPG loads in about 200ms, while a 5 MB PNG of the same image would take roughly 2 seconds - a difference that directly affects Google's Core Web Vitals score (Largest Contentful Paint).

For e-commerce, news, and content-heavy sites where hero images and product photos are the Largest Contentful Paint element, choosing JPG over PNG for photographic assets can be the single highest-impact performance optimisation available. Conversely, for UI elements like navigation icons and logos that are typically small regardless of format, the speed difference is negligible - a 10 KB PNG versus a 12 KB JPG icon adds less than 5ms of load time even on slow connections.

Browser decompression is also a factor, though less significant than download time: JPG decompression is slightly more CPU-intensive because it requires reconstructing the frequency-domain data, while PNG decompression is a straightforward DEFLATE stream. For web projects, the recommended approach is to use JPG (or modern WebP) for all photographic content, PNG for all transparent and graphic assets, and to implement lazy loading so that below-the-fold images do not block the critical rendering path.

Pour les Core Web Vitals de Google, le choix du format d'image affecte directement le Largest Contentful Paint (LCP). Une image hero servie en PNG volumineux peut facilement pousser le LCP au-delà du seuil de 2,5 s sur mobile, tandis que la même image en JPG ou WebP moderne reste généralement sous 1 s en connexion 4G. Si vous optimisez les performances web, pensez à nos outils d'optimisation d'images : compresseurs, convertisseurs de format et outils de redimensionnement qui fonctionnent entièrement dans votre navigateur.

PNG and JPG both enjoy effectively universal browser and operating system support - every browser released in the past 20 years, every mobile operating system, and every image editing application can read and write both formats without any plugins or special configurations. PNG was standardised by the W3C in 1996 and has been part of every major browser's core image rendering stack since the late 1990s; JPG (technically JPEG) dates back to 1992 and has been universally supported for even longer. This universality makes both formats safe choices for any web, mobile, or desktop application without worrying about compatibility matrices.

The practical difference in compatibility appears in how downstream platforms handle each format: social media platforms (Instagram, Facebook, Twitter/X) frequently transcode PNG uploads into JPG automatically to save storage and bandwidth, which means PNG transparency is lost and an additional round of lossy compression is applied - so for social media, starting with JPG avoids double compression. Email clients universally support both formats in HTML emails, though JPG is preferred for large photographs to reduce email load times.

Print workflows and professional design tools (Adobe Photoshop, Illustrator, Affinity Designer, Figma) fully support both formats, with PNG preferred for assets that need to be composed against variable backgrounds. If you are evaluating more modern alternatives, WebP offers better compression than both formats for both photographic and graphic content, and AVIF offers compression ratios up to 50% better than JPG - though both require consideration of older browser support if you need to target Internet Explorer or very old Safari versions.

Les deux formats bénéficient d'un support pratiquement universel sur tous les navigateurs modernes et systèmes d'exploitation. Pour les projets ciblant des navigateurs anciens ou des systèmes embarqués, PNG comme JPG sont des choix sûrs. Si vous évaluez des alternatives modernes plus performantes, pensez à la conversion en WebP (pris en charge par tous les navigateurs publiés après 2020) ou AVIF pour des ratios de compression de nouvelle génération jusqu'à 50% meilleurs que JPG.