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本案例的目的是理解如何用Metal实现海报画效果滤镜，主要就是改变颜色级别数量从而获取到新的像素颜色；
Demo
实操代码
// 海报画滤镜
let filter = C7Posterize.init(colorLevels: 2.3)
// 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
| colorLevels: 1.03 | colorLevels: 2.3 | colorLevels: 5.03 |
|---|---|---|
实现原理
- 过滤器
这款滤镜采用并行计算编码器设计.compute(kernel: "C7Posterize")，参数因子[colorLevels]；
对外开放参数
colorLevels: 减少图像空间的颜色级别数量；
public struct C7Posterize: C7FilterProtocol {
public static let range: ParameterRange<Float, Self> = .init(min: 1.0, max: 255.0, value: 10.0)
/// The number of color levels to reduce the image space to.
/// This ranges from 1 to 256, with a default of 10
public var colorLevels: Float = range.value
public var modifier: Modifier {
return .compute(kernel: "C7Posterize")
}
public var factors: [Float] {
return [colorLevels]
}
public init(colorLevels: Float = range.value) {
self.colorLevels = colorLevels
}
}
- 着色器
对输入像素x颜色级别数量再加上平均亮度half4(0.5h)取整floor，再除以颜色级别数量得到最终的像素颜色；
kernel void C7Posterize(texture2d<half, access::write> outputTexture [[texture(0)]],
texture2d<half, access::read> inputTexture [[texture(1)]],
constant float *colorLevelsPointer [[buffer(0)]],
uint2 grid [[thread_position_in_grid]]) {
const half4 inColor = inputTexture.read(grid);
const half colorLevels = half(*colorLevelsPointer);
const half4 outColor = floor((inColor * colorLevels) + half4(0.5h)) / colorLevels;
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。
✌️.
