Read-only dry run: runs the full optimisation in memory and reports, per image, the format Optiq would choose, bytes before and after, and the measured quality (SSIM, or pixel-exact). Writes nothing. Use it first to show the user the expected savings, then call optimize_images with the same arguments. Main parameters: paths (files or folders), mode (how strict the quality check is), keepFormat/formats (whether and to what the format may change), maxSize (downscale), stripMetadata (drop EXIF/GPS). Cost: it does the same work as optimize_images, several encodes per image, typically 0.3-3 s per image on a modern laptop (fast mode is quicker; very large screenshots in visually-lossless can take tens of seconds). For hundreds of images, try one subfolder first. Progress is reported per file and the call can be cancelled.

Optimises images and writes the results. If the user only wants to know how much could be saved, or has not agreed to changes yet, use analyze_images instead: it takes the same arguments and writes nothing. write: "in-place" overwrites each file and keeps its format and name, so references in code stay valid (atomic rename). write: "out-dir" writes to outDir, mirroring the folder structure, and may change formats; extensions change accordingly, so update references. A file is only replaced when the result passes the quality check and is smaller. Files Optiq already compressed lossily are skipped (unless reoptimize is true), so calling this twice is safe. Choosing parameters: mode visually-lossless for hero images, artwork and product photos, lossless for logos and UI assets that must stay exact, balanced otherwise; stripMetadata before publishing personal photos (GPS); formats without avif if old browsers matter. Takes the same time as analyze_images (typically 0.3-3 s per image).