图文并茂带你走进Core Image

Core Image is an image processing and analysis technology designed to provide near real-time processing for still and video images. It operates on image data types from the Core Graphics, Core Video, and Image I/O frameworks, using either a GPU or CPU rendering path. Core Image hides the details of low-level graphics processing by providing an easy-to-use application programming interface (API). You don’t need to know the details of OpenGL or OpenGL ES to leverage the power of the GPU, nor do you need to know anything about Grand Central Dispatch (GCD) to get the benefit of multicore processing. Core Image handles the details for you.

这一部分会结合代码，开发环境swift5.0。

/*
输出
*/
@available(iOS 5.0, *)
    open var outputImage: CIImage? { get }

    
    /* The name of the filter. On OSX and iOS 10, this property is read-write.
     * This can be useful when using CIFilters with CoreAnimation or SceneKit.
     * For example, to set an attribute of a filter attached to a layer,
     * a unique path such as "filters.myExposureFilter.inputEV" could be used.
     * CALayer animations may also access filter attributes via key-paths. */
/*
滤镜名
*/
    open var name: String

/*
滤镜输入参数
*/ 
    /** Returns an array containing the names of all inputs in the filter. */
    open var inputKeys: [String] { get }

 /*
滤镜输出参数
*/  
    /** Returns an array containing the names of all outputs in the filter. */
    open var outputKeys: [String] { get }

 /*
*/  
    /** Sets all inputs to their default values (where default values are defined, other inputs are left as-is). */
    open func setDefaults()

/*
滤镜支持的关键字
*/   
    /** Returns a dictionary containing key/value pairs describing the filter. (see description of keys below) */
    open var attributes: [String : Any] { get }

/* Categories */
/*失真效果，改变几何形状创建3D效果
比如bump、旋转、hole
*/
public let kCICategoryDistortionEffect: String
/*
扭曲图片和纠正源图像问题，例如仿射变换来校正相对于地平线旋转的图像
比如仿射变换、平切、透视转换
*/
public let kCICategoryGeometryAdjustment: String
/*
合成滤镜，操作两个图像源
比如源覆盖（source over）、最小化、源在顶（source atop）、色彩混合模式
*/
public let kCICategoryCompositeOperation: String
/*
半色调效果
比如screen、line screen、hatched
*/
public let kCICategoryHalftoneEffect: String
/*
色彩调整，用于消除色彩偏移、校正亮度和对比度
比如伽马调整、白点调整、曝光
*/
public let kCICategoryColorAdjustment: String
/*
色彩效果，我们一般用的比较多，类似美图工具的滤镜效果
比如色调调整、posterize
*/
public let kCICategoryColorEffect: String
/*
图像间转换
比如dissolve、disintegrate with mask、swipe
*/
public let kCICategoryTransition: String
/*
瓦片效果 平铺图片
比如parallelogram、triangle
*/
public let kCICategoryTileEffect: String
/*
图案的过滤器，如纯色、棋盘或星星的光泽。生成的输出通常用作对另一个过滤器的输入。
比如stripes、constant color、checkerboard
*/
public let kCICategoryGenerator: String
@available(iOS 5.0, *)
/*
减少图像数据 解决图像分析问题
*/
public let kCICategoryReduction: String
/*
渐变效果
比如轴向渐变、仿射渐变、高斯渐变
*/
public let kCICategoryGradient: String
/*
风格化
比如像素化、水晶化
*/
public let kCICategoryStylize: String
/*
锐化图像 锐化掩模和提高亮度
*/
public let kCICategorySharpen: String
/*
柔滑图像，主要用于模糊图像
比如高斯模糊、焦点模糊、运动模糊
*/
public let kCICategoryBlur: String
/*
处理视频图像
*/
public let kCICategoryVideo: String
/*
处理静态图像
*/
public let kCICategoryStillImage: String
/*
处理交错图像
*/
public let kCICategoryInterlaced: String
/*
处理非方形图像
*/
public let kCICategoryNonSquarePixels: String
/*
处理高动态图像
*/
public let kCICategoryHighDynamicRange: String
/*
用于区分built-in filters  plug-in filters.
*/
public let kCICategoryBuiltIn: String
@available(iOS 9.0, *)
/*
链接几个过滤器
*/
public let kCICategoryFilterGenerator: String

//获取kCICategoryDistortionEffect类型所有滤镜的名字和属性设置
        let filterArr = CIFilter.filterNames(inCategory: kCICategoryDistortionEffect)
        filterArr.forEach { (filterName) in
            let filter = CIFilter(name: filterName)
            let attributes = filter?.attributes
            
            print("------\nfilter name is:\n\(filterName) \nfilter attributes is :\n\(String(describing: attributes))\n\n")
        }

------
filter name is:
CIBumpDistortion 
filter attributes is :
Optional(["CIAttributeFilterAvailable_iOS": 6, "CIAttributeFilterCategories": <__NSArrayI 0x1c44457f0>(
CICategoryDistortionEffect,
CICategoryVideo,
CICategoryStillImage,
CICategoryBuiltIn
)
, "CIAttributeFilterDisplayName": Bump Distortion, "inputImage": {
    CIAttributeClass = CIImage;
    CIAttributeDescription = "The image to use as an input image. For filters that also use a background image, this is the foreground image.";
    CIAttributeDisplayName = Image;
    CIAttributeType = CIAttributeTypeImage;
}, "inputScale": {
    CIAttributeClass = NSNumber;
    CIAttributeDefault = "0.5";
    CIAttributeDescription = "The scale of the effect determines the curvature of the bump. A value of 0.0 has no effect. Positive values create an outward bump; negative values create an inward bump.";
    CIAttributeDisplayName = Scale;
    CIAttributeIdentity = 0;
    CIAttributeSliderMax = 1;
    CIAttributeSliderMin = "-1";
    CIAttributeType = CIAttributeTypeScalar;
}, "CIAttributeFilterName": CIBumpDistortion, "CIAttributeFilterAvailable_Mac": 10.4, "inputRadius": {
    CIAttributeClass = NSNumber;
    CIAttributeDefault = 300;
    CIAttributeDescription = "The radius determines how many pixels are used to create the distortion. The larger the radius, the wider the extent of the distortion.";
    CIAttributeDisplayName = Radius;
    CIAttributeMin = 0;
    CIAttributeSliderMax = 600;
    CIAttributeSliderMin = 0;
    CIAttributeType = CIAttributeTypeDistance;
}, "CIAttributeReferenceDocumentation": http://developer.apple.com/library/ios/documentation/GraphicsImaging/Reference/CoreImageFilterReference/index.html#//apple_ref/doc/filter/ci/CIBumpDistortion, "inputCenter": {
    CIAttributeClass = CIVector;
    CIAttributeDefault = "[150 150]";
    CIAttributeDescription = "The center of the effect as x and y coordinates.";
    CIAttributeDisplayName = Center;
    CIAttributeType = CIAttributeTypePosition;
}])

------------------------
太多，没有完全列举，请自行打印
------------------------

@available(iOS 5.0, *)
public let kCIOutputImageKey: String
@available(iOS 5.0, *)
public let kCIInputBackgroundImageKey: String
@available(iOS 5.0, *)
public let kCIInputImageKey: String
@available(iOS 11.0, *)
public let kCIInputDepthImageKey: String
@available(iOS 11.0, *)
public let kCIInputDisparityImageKey: String
@available(iOS 12.0, *)
public let kCIInputAmountKey: String
@available(iOS 7.0, *)
public let kCIInputTimeKey: String
@available(iOS 7.0, *)
public let kCIInputTransformKey: String
@available(iOS 7.0, *)
public let kCIInputScaleKey: String
@available(iOS 7.0, *)
public let kCIInputAspectRatioKey: String
@available(iOS 7.0, *)
public let kCIInputCenterKey: String
@available(iOS 7.0, *)
public let kCIInputRadiusKey: String
@available(iOS 7.0, *)
public let kCIInputAngleKey: String
@available(iOS 9.0, *)
public let kCIInputRefractionKey: String
@available(iOS 7.0, *)
public let kCIInputWidthKey: String
@available(iOS 7.0, *)
public let kCIInputSharpnessKey: String
@available(iOS 7.0, *)
public let kCIInputIntensityKey: String
@available(iOS 7.0, *)
public let kCIInputEVKey: String
@available(iOS 7.0, *)
public let kCIInputSaturationKey: String
@available(iOS 7.0, *)
public let kCIInputColorKey: String
@available(iOS 7.0, *)
public let kCIInputBrightnessKey: String
@available(iOS 7.0, *)
public let kCIInputContrastKey: String
@available(iOS 9.0, *)
public let kCIInputBiasKey: String
@available(iOS 9.0, *)
public let kCIInputWeightsKey: String
@available(iOS 9.0, *)
public let kCIInputGradientImageKey: String
@available(iOS 7.0, *)
public let kCIInputMaskImageKey: String
@available(iOS 12.0, *)
public let kCIInputMatteImageKey: String
@available(iOS 9.0, *)
public let kCIInputShadingImageKey: String
@available(iOS 7.0, *)
public let kCIInputTargetImageKey: String
@available(iOS 7.0, *)
public let kCIInputExtentKey: String
@available(iOS 6.0, *)
public let kCIInputVersionKey: String

func imageFilter(with image: UIImage, filterName: String, inputValue: [String: Any]) -> UIImage? {
    //将UIImage转换成CIImage,处理前的图片
    guard let input = CIImage(image:image) else {
        return nil
    }
    
    //通过名字创建CIFilter滤镜
    let filter = CIFilter(name: filterName, parameters: [kCIInputImageKey: input])
    
    // 用KVC给CIFilter设置滤镜参数，可直接在上面的初始化方法中加到parameters
    filter?.setValue(input, forKey: kCIInputImageKey)
    
    //渲染并输出CIImage，处理后的图片
    guard let output = filter?.outputImage else {
        return nil
    }
    
    //创建CIContext上下文
    let context = CIContext(options: nil)
    
    //初始化CGImageRef对象，创建输出CGImage，赋给UIImage对象
    //注意，我们使用输入图像大小的原因是，输出图像通常和输入图像具有不同的尺寸比。例如，一个模糊图像由于采样超出了输入图像的边缘，围绕在其边界外还会有一些额外的像素。
    guard let cgImage = context.createCGImage(output, from: input.extent) else {
        return nil
    }

    let uiImage = UIImage(cgImage: cgImage)
    
    
    return uiImage
}

if let image = UIImage(named: "girl") {
        let inputValue = ["inputRadius": 10.0]
        let output = imageFilter(with: image, filterName: "CIColorMonochrome", inputValue: inputValue)
}

// 创建基于 CPU 的 CIContext 对象 (默认是基于 GPU，CPU 需要额外设置参数)
context = [CIContext contextWithOptions: [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:kCIContextUseSoftwareRenderer]];

// 创建基于 GPU 的 CIContext 对象
context = [CIContext contextWithOptions: nil];

// 创建基于 GPU 的 CIContext 对象
EAGLContext *eaglctx = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
context = [CIContext contextWithEAGLContext:eaglctx];