Metal每日分享，颜色转换滤镜效果

「这是我参加2022初次更文应战的第4天，活动概况检查：2022初次更文应战」

本案例的意图是了解如何用Metal实现像素色彩转化滤镜，通过对像素色彩的不同读取方式获取到相应像素色彩，灰度图移除场景中除了黑白灰以外一切的色彩，让整个图画灰度化；

Demo

• HarbethDemo地址
• iDay每日共享文档地址

实操代码

// 转成灰度图滤镜
let filter = C7ColorConvert(with: .gray)
// 计划1:
let dest = BoxxIO.init(element: originImage, filter: filter)
ImageView.image = try? dest.output()
dest.filters.forEach {
  NSLog("%@", "\($0.parameterDescription)")
}
// 计划2:
ImageView.image = try? originImage.make(filter: filter)
// 计划3:
ImageView.image = originImage ->> filter

实现原理

• 过滤器

这款滤镜采用并行计算编码器规划.compute(kernel: type.rawValue)

/// 色彩通道`RGB`位置转化
public struct C7ColorConvert: C7FilterProtocol {
    public enum ColorType: String, CaseIterable {
        case invert = "C7ColorInvert"
        case gray = "C7Color2Gray"
        case bgra = "C7Color2BGRA"
        case brga = "C7Color2BRGA"
        case gbra = "C7Color2GBRA"
        case grba = "C7Color2GRBA"
        case rbga = "C7Color2RBGA"
    }
    private let type: ColorType
    public var modifier: Modifier {
        return .compute(kernel: type.rawValue)
    }
    public init(with type: ColorType) {
        self.type = type
    }
}

• 着色器

取出像素rgb值，然后根据对应像素色彩；灰度图则是取一切的色彩重量，将它们加权或均匀；

// 色彩反转，1 - rgb
kernel void C7ColorInvert(texture2d<half, access::write> outputTexture [[texture(0)]],
                          texture2d<half, access::read> inputTexture [[texture(1)]],
                          uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(1.0h - inColor.rgb, inColor.a);
    outputTexture.write(outColor, grid);
}
// 转灰度图
kernel void C7Color2Gray(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half3 kRec709Luma = half3(0.2126, 0.7152, 0.0722);
    const half gray = dot(inColor.rgb, kRec709Luma);
    const half4 outColor = half4(half3(gray), 1.0h);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2BGRA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.bgr, inColor.a);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2BRGA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.brg, inColor.a);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2GBRA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.gbr, inColor.a);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2GRBA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.grb, inColor.a);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2RBGA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.rbg, inColor.a);
    outputTexture.write(outColor, grid);
}

• 权值法

const half3 kRec709Luma = half3(0.2126, 0.7152, 0.0722);
const half gray = dot(inColor.rgb, kRec709Luma);
const half4 outColor = half4(half3(gray), 1.0h);

• 均匀值法

const float color = (inColor.r + inColor.g + inColor.b) / 3.0;
const half4 outColor = half4(color, color, color, 1.0h);

总结：
一般因为人眼对不同色彩的敏感度不一样，所以三种色彩值的权重不一样，一般来说绿色最高，赤色其次，蓝色最低，最合理的取值分别为Wr ＝ 30％，Wg ＝ 59％，Wb ＝ 11％，所以权值法相对作用更好一点。

对照图

invert	bgra	brga
gbra	grba	rbga

Harbeth功用清单

• 支撑ios体系和macOS体系
• 支撑运算符函数式操作
• 支撑多种形式数据源 UIImage, CIImage, CGImage, CMSampleBuffer, CVPixelBuffer.
• 支撑快速规划滤镜
• 支撑合并多种滤镜作用
• 支撑输出源的快速扩展
• 支撑相机采集特效
• 支撑视频增加滤镜特效
• 支撑矩阵卷积
• 支撑运用体系 MetalPerformanceShaders.
• 支撑兼容 CoreImage.
• 滤镜部分大致分为以下几个模块：
  • Blend：图画融合技术
  • Blur：模糊作用
  • Pixel：图画的基本像素色彩处理
  • Effect：作用处理
  • Lookup：查找表过滤器
  • Matrix: 矩阵卷积滤波器
  • Shape：图画形状大小相关
  • Visual: 视觉动态特效
  • MPS: 体系 MetalPerformanceShaders.

最后

• 关于色彩转化滤镜介绍与规划到此为止吧。
• 慢慢再弥补其他相关滤镜，喜欢就给我点个星吧。
• 滤镜Demo地址，现在包含100+种滤镜，同时也支撑CoreImage混合运用。
• 再附上一个开发加速库KJCategoriesDemo地址
• 再附上一个网络根底库RxNetworksDemo地址
• 喜欢的老板们可以点个星，谢谢各位老板！！！

✌️.