Read, write, and convert formats

The input is input.jpg; the output is output.webp. These examples show the shape of each binding. The reference output was produced by govips and passed format and dimension checks.

Gate of the Orient outlined in red lights above a park walkway at night — **Input: JPEG**1938 × 1292, 610,191 bytes

The same night scene converted to WebP without changing its dimensions — **Reference output: WebP**1938 × 1292, 399,106 bytes, quality 82

All four bindings have passed format and dimension checks; encoded bytes from different libvips versions are not expected to be identical.

package main

import (
    "fmt"
    "os"

    "github.com/davidbyttow/govips/v2/vips"
)

func main() {
    if err := vips.Startup(nil); err != nil {
        return err
    }
    defer vips.Shutdown()

    image, err := vips.NewImageFromFile("input.jpg")
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        os.Exit(1)
    }
    defer image.Close()

    params := vips.NewWebpExportParams()
    params.Quality = 82
    data, _, err := image.ExportWebp(params)
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        os.Exit(1)
    }
    if err := os.WriteFile("output.webp", data, 0o644); err != nil {
        fmt.Fprintln(os.Stderr, err)
        os.Exit(1)
    }
}

import sharp from 'sharp';

try {
  await sharp('input.jpg')
    .webp({ quality: 82 })
    .toFile('output.webp');
} catch (error) {
  console.error(error);
  process.exitCode = 1;
}

import sys
import pyvips

try:
    image = pyvips.Image.new_from_file("input.jpg", access="sequential")
    image.write_to_file("output.webp", Q=82)
except pyvips.Error as error:
    print(error, file=sys.stderr)
    raise SystemExit(1) from error

#!/usr/bin/env bash
set -euo pipefail

vips copy input.jpg 'output.webp[Q=82]'

More than a file-extension change

Format conversion decodes and re-encodes pixels. Output quality, metadata, ICC profiles, alpha, animation pages, and codec availability can all change. Quality = 100 or Q=100 does not mean lossless; lossless encoding is a separate choice.

Sources

The topic and govips example shape came from the older Chinese notes; resource cleanup and error handling were added here.
libvips WebP saver options
sharp output options