Metal每日分享,自然饱和度滤镜效果

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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

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: -1.2vibrance: -0.5vibrance: 1.0
WX20221220-090820.pngWX20221220-090653.pngWX20221220-090709.png

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 0.0
    public var vibrance: Float = range.value
    
    public 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);
}

最后

  • 慢慢再补充其他相关滤镜,喜欢就给我点个星🌟吧。

✌️.