Format behavior

imgsqz doesn’t just pass your file to a generic encoder — it applies tuned sharp settings per format. This page documents exactly what happens for each -f value.

JPG (-f jpg / -f jpeg)

sharp(...).jpeg({ quality, mozjpeg: true, progressive: true })

• mozjpeg encoder — meaningfully smaller files than the standard JPEG encoder at the same quality.
• Progressive — renders top-to-bottom in increasing detail; usually a touch smaller and nicer on slow connections.
• No alpha channel (JPG has no transparency).
• quality from -q (default 80).

Tip

mozjpeg means imgsqz can often re-compress an existing JPG smaller with little visible change — handy for trimming oversized photos.

PNG (-f png)

sharp(...).png({ quality, compressionLevel: 9, palette: !lossless })

• compressionLevel: 9 — maximum zlib compression (slower, smallest).
• Palette quantization is on by default (palette: true), which uses quality to reduce the color palette — big savings for graphics, logos, and flat-color images.
• Passing --lossless sets palette: false, preserving full color depth (no quantization) for a truly lossless PNG.
• Alpha channel (transparency) preserved.

# Quantized PNG (smaller, palette-based)
imgsqz logo.png -f png -q 70

# Full-depth lossless PNG
imgsqz art.png -f png --lossless

WebP (-f webp)

sharp(...).webp({ quality, lossless, effort: 5 })

• effort: 5 — a balanced CPU/size setting (range is 0–6; higher is slower and slightly smaller).
• --lossless switches to lossless WebP (exact pixels, alpha preserved).
• Alpha channel preserved in both modes.
• Excellent default choice for the web.

imgsqz photo.png -f webp -q 75            # lossy
imgsqz screenshot.png -f webp --lossless  # lossless

AVIF (-f avif)

sharp(...).avif({ quality, lossless, effort: 5 })

• effort: 5 — balanced encode speed vs. size (range 0–9 in libvips; imgsqz uses 5).
• --lossless for exact reconstruction.
• Best-in-class compression for photos — typically smaller than WebP at similar perceived quality.
• Encoding is more CPU-intensive than WebP/JPG; expect longer runs on large batches.

imgsqz photo.jpg -f avif -q 50    # great size for the web

TIFF (-f tiff)

sharp(...).tiff({ quality, compression: "lzw" })

• LZW compression — lossless container compression suited to archival and print workflows.
• quality is accepted for completeness; LZW is lossless, so the practical output is a losslessly compressed TIFF.
• --lossless has no additional effect here (TIFF/LZW is already lossless).

imgsqz scan.png -f tiff

How flags map to formats

Flag	jpg	png	webp	avif	tiff
--quality	✅	✅ (palette)	✅	✅	⚪️ (LZW lossless)
--lossless	⚪️	✅ (disables palette)	✅	✅	⚪️ (already lossless)
Transparency	❌	✅	✅	✅	✅
--grayscale	✅	✅	✅	✅	✅
--width/--height	✅	✅	✅	✅	✅
--no-strip-metadata	✅	✅	✅	✅	✅

✅ applies · ⚪️ accepted but no effect · ❌ not supported by the format

Always-on processing

Regardless of format, every pipeline:

1. Opens the source with failOn: "none" — tolerant of minor corruption so slightly malformed images still process.
2. Auto-rotates using EXIF orientation (.rotate()), baking the upright orientation into the pixels.
3. Applies resize → grayscale → metadata → encode, in that order (see Core concepts).