コマンドラインから画像リサイズ（swift1.2） ref: http://qiita.com/MTattin/items/93a8fdf7bb6ad58e8011

swift

#!/usr/bin/swift


import Cocoa


class fileMG {

    var dir:  String
    var file: String
    var path: String
    var extn: String

    init(p: String) {
        path = p
        file = p.lastPathComponent
        dir  = p.stringByReplacingOccurrencesOfString(file, withString: "", options: nil, range: nil)
        extn = p.pathExtension
    }
}


class imgMG: fileMG {

    func resizeImg(#w: Int, h: Int) -> String {

        if let img: NSImage = NSImage(contentsOfFile: path) {

            let orgBmpRep: NSBitmapImageRep = NSBitmapImageRep(data:img.TIFFRepresentation!)!
            let orgRef:    CGImage          = orgBmpRep.CGImage!
            let orgW:      Int              = Int(CGImageGetWidth(orgRef))
            let orgH:      Int              = Int(CGImageGetHeight(orgRef))

            var resizeW: Int = 0, resizeH: Int = 0
            if (orgW < orgH) {
                resizeW  = w
                resizeH = orgH * resizeW / orgW
            } else {
                resizeH = h
                resizeW = orgW * resizeH / orgH
            }
            let resizeSize: NSSize = NSMakeSize(CGFloat(resizeW), CGFloat(resizeH))

            let bitsPerComponent: Int          = 8
            let bytesPerRow:      Int          = 4 * resizeW
            let colorSpace:       CGColorSpace = CGColorSpaceCreateDeviceRGB()
            let bitmapInfo:       CGBitmapInfo = CGBitmapInfo(
                                                     CGImageAlphaInfo.PremultipliedLast.rawValue)

            let bitmapContext: CGContextRef = CGBitmapContextCreate(
                                                  nil,
                                                  resizeW,
                                                  resizeH,
                                                  bitsPerComponent,
                                                  bytesPerRow,
                                                  colorSpace,
                                                  bitmapInfo)

            // 元画像 (image) をビットマップに書き出します。
            let bitmapRect: CGRect = NSMakeRect(0.0, 0.0, resizeSize.width, resizeSize.height)
            CGContextDrawImage(bitmapContext, bitmapRect, orgRef)

            // ビットマップを NSImage に変換します。
            let newImageRef: CGImageRef = CGBitmapContextCreateImage(bitmapContext)!
            let newImage:    NSImage    = NSImage(CGImage: newImageRef, size: resizeSize)

            // p保存
            let newBmpRep:  NSBitmapImageRep = NSBitmapImageRep(data:newImage.TIFFRepresentation!)!
            let imageProps: NSDictionary     = NSDictionary(
                                                   objects: [1.0] as [AnyObject],
                                                   forKeys: [NSImageCompressionFactor] as [AnyObject])
            let newData:    NSData           = newBmpRep.representationUsingType(
                                                  NSBitmapImageFileType.NSPNGFileType,
                                                  properties: imageProps as [NSObject : AnyObject])!
            let wk:         [String]         = file.componentsSeparatedByString(".")
            let newFile:    String           = wk[0] + "_" + String(w) + "." + extn
            let newPath:    String           = dir.stringByAppendingPathComponent(newFile)

            newData.writeToFile(newPath, atomically: true)
            return newPath

        } else {
            return "not file : " + path

        }
    }
}

if (Process.arguments.count <= 1) {
    println("画像ファイルを指定してください")
    exit(0)
}
var imgResize = imgMG(p: String(Process.arguments[1]))

println(imgResize.resizeImg(w:  50, h:  50))
println(imgResize.resizeImg(w: 100, h: 100))
println(imgResize.resizeImg(w: 300, h: 300))