如何应用自定义过滤器

Question

我正在使用 AlamofireImage 从我的 CDN 下载图像，但是我想对下载的某些图像应用自定义过滤器（灰度）。目前我正在使用 scrollView 来显示所有可用图像，如果图像具有特定属性，则应用过滤器。

我是 AlamofireImage 的新手，所以我不知道如何应用自定义过滤器。

我已经申请

let imageFilter = BlurFilter(blurRadius: 10)

到过滤器参数，所以我知道实际的过滤器过程正在工作，但有人可以帮助创建自定义过滤器以将灰度应用于下载的图像吗？

Answer 1

方法#1

使用 Alamofireimage 的“imageWithAppliedCoreImageFilter” UIImage 扩展。但出于某种原因，他们没有提供对这个过滤器选项的简单协议访问，所以让我们创建一个......

public struct CoreImageFilter: ImageFilter {

    let filterName: String
    let parameters: [String: AnyObject]

    public init(filterName : String, parameters : [String : AnyObject]?) {
        self.filterName = filterName
        self.parameters = parameters ?? [:]
    }

    public var filter: UIImage -> UIImage {
        return { image in
            return image.af_imageWithAppliedCoreImageFilter(self.filterName, parameters: self.parameters) ?? image
    }
}

Alamofireimage 用户应该熟悉用法：

let imageView = UIImageView(frame: frame)
let URL = NSURL(string: "https://httpbin.org/image/png")!
let placeholderImage = UIImage(named: "placeholder")!
let color = CIColor(color: UIColor.grayColor())  // or whatever color desired
let intensity = 1.0  // 1.0 is the default, but setting it manually here to allow adjustment
let filter = CoreImageFilter(filterName: "CIColorMonochrome", parameters: ["inputColor": color, "inputIntensity" : intensity])

imageView.af_setImageWithURL(
    URL,
    placeholderImage: placeholderImage,
    filter: filter
)

如果您对 CIColorMonochrome 过滤器不满意（我不满意），这里有一些其他选择...

let filter = CoreImageFilter(filterName: "CIPhotoEffectTonal", parameters: nil)

或者

let filter = CoreImageFilter(filterName: "CIPhotoEffectNoir", parameters: nil)

这是Apple 开发站点上可用过滤器完整列表的链接。

方法#2

查找自定义滤镜，例如最受好评的答案是什么是产生黑白效果的最佳核心图像滤镜？.

然后创建一个扩展。信用Shmidt和DerGote为下面的代码的身体。

extension UIImage {
    public func ff_imageFilteredToGrayScale() -> UIImage? {
        let context = CIContext(options: nil)
        let ciImage = CoreImage.CIImage(image: self)!

        // Set image color to b/w
        let bwFilter = CIFilter(name: "CIColorControls")!
        bwFilter.setValuesForKeysWithDictionary([kCIInputImageKey:ciImage, kCIInputBrightnessKey:NSNumber(float: 0.0), kCIInputContrastKey:NSNumber(float: 1.1), kCIInputSaturationKey:NSNumber(float: 0.0)])
        let bwFilterOutput = (bwFilter.outputImage)!

        // Adjust exposure
        let exposureFilter = CIFilter(name: "CIExposureAdjust")!
        exposureFilter.setValuesForKeysWithDictionary([kCIInputImageKey:bwFilterOutput, kCIInputEVKey:NSNumber(float: 0.7)])
        let exposureFilterOutput = (exposureFilter.outputImage)!

        // Create UIImage from context
        let bwCGIImage = context.createCGImage(exposureFilterOutput, fromRect: ciImage.extent)
        let resultImage = UIImage(CGImage: bwCGIImage, scale: 1.0, orientation: self.imageOrientation)

        return resultImage
    }
}

和结构...

public struct GrayScaleFilter: ImageFilter {

    public init() {
    }

    public var filter: UIImage -> UIImage {
        return { image in
            return image.ff_imageFilteredToGrayScale() ?? image
        }
    }
}

最后，用法...

let imageView = UIImageView(frame: frame)
let URL = NSURL(string: "https://httpbin.org/image/png")!
let placeholderImage = UIImage(named: "placeholder")!

let filter = GrayScaleFilter()

imageView.af_setImageWithURL(
    URL,
    placeholderImage: placeholderImage,
    filter: filter
)