pdf2jpeg.swift

import Foundation
import CoreGraphics
import ImageIO
import UniformTypeIdentifiers

// Usage: swift pdf2jpeg.swift <input.pdf> <outdir> <dpi> <quality>
let args = CommandLine.arguments
guard args.count >= 3 else {
    FileHandle.standardError.write("usage: pdf2jpeg <input.pdf> <outdir> [dpi] [quality]\n".data(using: .utf8)!)
    exit(1)
}
let inputPath = args[1]
let outDir = args[2]
let dpi: CGFloat = args.count > 3 ? CGFloat(Double(args[3]) ?? 150) : 150
let quality: CGFloat = args.count > 4 ? CGFloat(Double(args[4]) ?? 0.9) : 0.9
let scale = dpi / 72.0

let url = URL(fileURLWithPath: inputPath)
guard let doc = CGPDFDocument(url as CFURL) else {
    FileHandle.standardError.write("error: could not open PDF\n".data(using: .utf8)!)
    exit(1)
}

try? FileManager.default.createDirectory(atPath: outDir, withIntermediateDirectories: true)

let pageCount = doc.numberOfPages
let pad = String(pageCount).count

for i in 1...pageCount {
    guard let page = doc.page(at: i) else { continue }
    let box = page.getBoxRect(.cropBox)
    let w = Int((box.width * scale).rounded())
    let h = Int((box.height * scale).rounded())

    let cs = CGColorSpaceCreateDeviceRGB()
    guard let ctx = CGContext(data: nil, width: w, height: h, bitsPerComponent: 8,
                              bytesPerRow: 0, space: cs,
                              bitmapInfo: CGImageAlphaInfo.noneSkipLast.rawValue) else { continue }
    // white background
    ctx.setFillColor(red: 1, green: 1, blue: 1, alpha: 1)
    ctx.fill(CGRect(x: 0, y: 0, width: w, height: h))
    ctx.scaleBy(x: scale, y: scale)
    ctx.translateBy(x: -box.origin.x, y: -box.origin.y)
    ctx.drawPDFPage(page)

    guard let image = ctx.makeImage() else { continue }
    let num = String(format: "%0\(pad)d", i)
    let outURL = URL(fileURLWithPath: outDir).appendingPathComponent("page-\(num).jpg")
    guard let dest = CGImageDestinationCreateWithURL(outURL as CFURL, UTType.jpeg.identifier as CFString, 1, nil) else { continue }
    let opts: [CFString: Any] = [kCGImageDestinationLossyCompressionQuality: quality]
    CGImageDestinationAddImage(dest, image, opts as CFDictionary)
    if CGImageDestinationFinalize(dest) {
        print("wrote \(outURL.path) (\(w)x\(h))")
    } else {
        FileHandle.standardError.write("failed to write page \(i)\n".data(using: .utf8)!)
    }
}