Image output formats Last updated: 07. Jul 2026

Docly can deliver modern image formats (WebP / AVIF) with better compression via scaleImage and the site-wide default format.

Docly can deliver modern image formats with better compression. This applies to scaleImage, attachFile64 and the site-wide default (Images.DefaultFormat in site.json).

Available formats

Format	Value	Encoding	Use
JPEG	`jpeg`	GDI+ (fastest)	Standard, universal.
PNG	`png`	GDI+	Lossless / transparency.
WebP	`webp`	Magick.NET	Better compression than JPEG; universal browser support today.
AVIF	`avif`	Magick.NET	Best compression; modern browsers. Recommended for the highest performance score (Google's recommendation).
Auto	`auto` (default)	—	Preserve the source format (PNG → PNG), otherwise JPEG. Falls back to `Images.DefaultFormat` if set.

How to choose a format

Per call: docly.scaleImage(bytes, 1200, 800, 0, 80, "webp") — an explicit format always wins. quality (here 80) applies to WebP/AVIF too.
Site default: set Images.DefaultFormat: "webp" in site.json → every scaleImage call without an explicit format uses WebP.

// explicit AVIF, quality 60
var out = docly.scaleImage(bytes, 800, 600, 0, 60, "avif");

// or a site-wide default in site.json:
{ "Images": { "DefaultFormat": "webp" } }

Important limitation (document precisely): WebP/AVIF apply to scaleImage / attachFile64 (and the site default). The URL-based scaling (/photo.jpg/WxHxM/…) delivers JPEG. If you need WebP/AVIF on a link, generate the image with scaleImage and serve/store it yourself. See Image scaling & allowed sizes.