pdfcraft/crates/optimize

pdfcraft-optimize

Layer L4: the PDF Optimizer (execution plan M11.1; Acrobat's Reduce File Size and Optimize PDF ▸ Advanced optimization).

let report = optimize(&mut doc, &Settings::default())?;   // Reduce File Size's choices

• Images: the effective resolution of each image is measured where pages draw it (the CTM through form XObjects; the smallest over all uses). Colour and grayscale images above a threshold are resampled with a bicubic (Catmull-Rom) filter to a target resolution and stored as JPEG (Acrobat's quality steps) or ZIP; soft masks are resampled with their image. An image is replaced only if the result is smaller. Left alone: CMYK and other colour spaces, image masks, decode arrays, more than 8 bits, JPEG 2000, JBIG2 and CCITT.
• Discard objects: thumbnails, alternate images, document tags, print settings.
• Clean up: Flate for streams with no filter.

The engine runs Remove Hidden Information (pdfcraft-redact) for the user-data categories, then this, then merges identical objects and writes a full, compressed save. JPEG decoding and encoding and resampling come from the image crate.