本案例的目的是理解如何用Metal实现自然饱和度效果滤镜，简单讲就是调整图像整体的明亮程度，如调节到较高数值，图像会产生色彩过饱和从而引起图像失真；

Demo

  • HarbethDemo地址
  • iDay每日分享文档地址

实操代码

// 自然饱和度滤镜
let filter = C7Vibrance.init(vibrance: -1.2)// 方案1:
ImageView.image = try? BoxxIO(element: originImage, filters: [filter, filter2, filter3]).output()// 方案2:
ImageView.image = originImage.filtering(filter, filter2, filter3)// 方案3:
ImageView.image = originImage ->> filter ->> filter2 ->> filter3

效果对比图

  • 不同参数下效果
vibrance: -1.2 vibrance: -0.5 vibrance: 1.0

实现原理

  • 过滤器

这款滤镜采用并行计算编码器设计.compute(kernel: "C7Vibrance")，参数因子[vibrance]；

对外开放参数

  • vibrance: 将图像的振动从-1.2更改为1.2，默认值为0.0；
/// 自然饱和度
public struct C7Vibrance: C7FilterProtocol {public static let range: ParameterRange<Float, Self> = .init(min: -1.2, max: 1.2, value: 0.0)/// Change the vibrance of an image, from -1.2 to 1.2, with a default of 0.0public var vibrance: Float = range.valuepublic var modifier: Modifier {return .compute(kernel: "C7Vibrance")}public var factors: [Float] {return [vibrance]}public init(vibrance: Float = range.value) {self.vibrance = vibrance}
}
  • 着色器

计算出rgb的平均值，获取单通道颜色的最大值，得到饱和度计算后值amt，混合rgb和最大值和饱和度值得到最终的像素rgb；

kernel void C7Vibrance(texture2d<half, access::write> outputTexture [[texture(0)]],texture2d<half, access::read> inputTexture [[texture(1)]],constant float *vibrance [[buffer(0)]],uint2 grid [[thread_position_in_grid]]) {const half4 inColor = inputTexture.read(grid);const half average = (inColor.r + inColor.g + inColor.b) / 3.0h;const half mx = max(inColor.r, max(inColor.g, inColor.b));const half amt = (mx - average) * (-half(*vibrance) * 3.0h);const half4 outColor = half4(mix(inColor.rgb, half3(mx), amt), inColor.a);outputTexture.write(outColor, grid);
}

Harbeth功能清单

最后