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Options reference

Every option below is a field of CompressOptions. The same field names, values and defaults apply in Rust, JavaScript, Python, Go, PHP, Kotlin and Swift — only the spelling of the surrounding code changes (see the quickstarts).

Quality and format

Section titled “Quality and format”
Field Type Default Notes
quality u8, 1–100 80 JPEG/WebP quality. Outside 1–100 → INVALID_QUALITY. PNG ignores this and uses png_compression_level + palette.
format ImageFormat or null keep input format Explicit output format overrides the input format. Values: jpeg, png, webp, avif, gif, bmp.
lossless bool false WebP/PNG only. Ignored (not an error) for other formats.
effort u8 6 WebP 0–6; AVIF speed 0–10. Higher = smaller file, slower encode.
progressive bool false JPEG progressive / PNG interlaced.
subsampling S444 | S422 | S420 S420 for JPEG quality < 90, S444 otherwise Chroma subsampling (JPEG). S420 halves colour resolution and is the classic size saver; S444 keeps full colour.

PNG

Section titled “PNG”
Field Type Default Notes
png_compression_level u8, 0–9 6 PNG compression level. 9 is smallest and slowest.
palette bool false Quantise PNG to a 256-colour palette. Helps photographic PNGs; can make an already-tiny flat PNG larger (see the guide).

Presets and target size

Section titled “Presets and target size”
Field Type Default Notes
preset Web | Social | Print | Archive or null none Sets quality/effort/subsampling defaults; explicit fields override it. Exact values: Presets.
target_bytes u64 or null none Target-size search via the one-call path (same search as compress_to_size).

Resize

Section titled “Resize”
Field Type Default Notes
max_width u32 or null none Downscale-only, never upscale; aspect preserved.
max_height u32 or null none Downscale-only, never upscale; aspect preserved.

Set one or both. If the image is already within both limits, dimensions are unchanged and the report’s resized field is false.

Metadata, orientation, DPI

Section titled “Metadata, orientation, DPI”
Field Type Default Notes
strip_metadata All | KeepExif | KeepIcc | KeepAll All Which metadata survives compression.
auto_orient bool true Apply EXIF orientation on load, so the output is upright.
dpi (u32, u32) or null none Set DPI on JPEG/PNG output where supported.

Safety limits

Section titled “Safety limits”
Field Type Default Notes
max_pixels u64 120_000_000 Images with more pixels are refused with IMAGE_TOO_LARGE.
max_dimension u32 16000 Images wider or taller than this are refused with IMAGE_TOO_LARGE.

These exist because the whole image lives in memory — they stop a gigapixel input from exhausting RAM. Lower them if you run in a memory-constrained environment.

Enums

Section titled “Enums”
  • ImageFormat: jpeg, png, webp, avif, gif, bmp
  • Subsampling: S444, S422, S420
  • Preset: Web, Social, Print, Archive
  • StripMetadata: All, KeepExif, KeepIcc, KeepAll

Report fields

Section titled “Report fields”

compress_with_report (and bulk_compress per item) returns:

Field Type Meaning
output bytes The compressed image bytes.
original_size u64 Input size in bytes.
output_size u64 Output size in bytes.
saved_bytes u64 original_size - output_size.
saved_percent f32 100 * saved_bytes / original_size.
format ImageFormat Output format.
width, height u32 Output dimensions.
quality_used u8 Quality the encoder actually used.
resized bool True only if the dimensions changed.

Info fields

Section titled “Info fields”

get_image_info returns format, width, height, has_alpha, colour_type and file_size — without decoding the full pixel data.