Create variants for an image (based on https://github.com/tmcw/bespoke)

pl-convert.js

#!/usr/bin/env node

const fs = require('fs')
const sharp = require('sharp')
const prettyBytes = require('pretty-bytes')

// -------------------------------------------------------------
// Script.
//
// Note: for optimal file sizes, export at highest quality
// and resolution in Lightroom.
//
// I don't know why, but from all the tests I made, this is what
// gives the smallest file sizes for the images generated here.
// -------------------------------------------------------------

if (process.argv.length !== 3) {
  console.error('usage: pl-convert file.jpg')
  process.exit(0)
}

const RESOLUTIONS = [500, 1000, 1500, 2400]

const name = process.argv[2] // Get arg.
const shortname = name.replace(/\.[^/.]+$/, '') // Remove extension.
const image = fs.readFileSync(name) // Read file buffer.

// Export an image in 4 sizes and in 2 formats.
// Remove the metadata.
// Do not enlarge.
// Use largest edge for resize (if portrait, height, if landscape, width).
!(async () => {
  const {width, height} = await sharp(image).metadata()

  for (let res of RESOLUTIONS) {
    const jpg = `${shortname}_${res}.jpg`
    const webp = `${shortname}_${res}.webp`

    const options = {withoutEnlargement: true}
    if (width >= height) options.width = res
    else options.height = res

    await sharp(image).resize(options).jpeg({quality: 75}).toFile(jpg)
    await sharp(image).resize(options).webp({quality: 75}).toFile(webp)

    log(jpg)
    log(webp)
  }
})()

function log(filename) {
  const size = prettyBytes(fs.readFileSync(filename).byteLength)
  console.log(`${filename}: ${size}`)
}