Core Image 是一个强大的滤镜处理框架。它除了可以直接给图片添加各种内置滤镜，还能精确地修改鲜艳程度, 色泽, 曝光等，下面通过两个样例演示如何给 UIImage 添加滤镜。

1，棕褐色滤镜  - CISepiaTone

import UIKit

//--- UIImageFilterExtension.swift ---
extension UIImage
{
    //棕褐色复古滤镜（老照片效果）
    func sepiaTone() -> UIImage?
    {
        let imageData = UIImagePNGRepresentation(self)
        let inputImage = CoreImage.CIImage(data: imageData!)
        let context = CIContext(options:nil)
        let filter = CIFilter(name:"CISepiaTone")
        filter!.setValue(inputImage, forKey: kCIInputImageKey)
        filter!.setValue(0.8, forKey: "inputIntensity")
        if let outputImage = filter!.outputImage {
            let outImage = context.createCGImage(outputImage, from: outputImage.extent)
            return UIImage(cgImage: outImage!)
        }
        return nil
    }
}

使用样例：

imageView1.image = UIImage(named:"img2.jpg")?.sepiaTone()

2，黑白滤镜 - CIPhotoEffectNoir

import UIKit

//--- UIImageFilterExtension.swift ---
extension UIImage
{
    //黑白效果滤镜
    func noir() -> UIImage?
    {
        let imageData = UIImagePNGRepresentation(self)
        let inputImage = CoreImage.CIImage(data: imageData!)
        let context = CIContext(options:nil)
        let filter = CIFilter(name:"CIPhotoEffectNoir")
        filter!.setValue(inputImage, forKey: kCIInputImageKey)
        if let outputImage = filter!.outputImage {
            let outImage = context.createCGImage(outputImage, from: outputImage.extent)
            return UIImage(cgImage: outImage!)
        }
        return nil
    }
}

使用样例：

imageView1.image = UIImage(named:"img2.jpg")?.noir()