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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: -1.2 | 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 0.0
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。
✌️.
