46 lines
1.6 KiB
Swift
46 lines
1.6 KiB
Swift
import Foundation
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/// ASC CDL primary correction: out = clamp0(in * slope + offset)^power, then saturation.
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/// Saturation uses Rec709 luma weights per ASC CDL 1.2.
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public struct CDL: Equatable, Sendable {
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public var slope: SIMD3<Float>
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public var offset: SIMD3<Float>
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public var power: SIMD3<Float>
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public var saturation: Float
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public init(slope: SIMD3<Float>, offset: SIMD3<Float>, power: SIMD3<Float>, saturation: Float) {
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self.slope = slope
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self.offset = offset
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self.power = power
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self.saturation = saturation
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}
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public static let identity = CDL(slope: .one, offset: .zero, power: .one, saturation: 1)
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public var isIdentity: Bool { self == .identity }
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/// Rec709 luma weights (ASC CDL saturation spec).
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public static let lumaWeights = SIMD3<Float>(0.2126, 0.7152, 0.0722)
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public func apply(_ rgb: SIMD3<Float>) -> SIMD3<Float> {
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// SOP, clamped to >=0 before power for determinism (ASC pre-power clamp).
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let sop = rgb * slope + offset
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let zero = SIMD3<Float>.zero
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let clamped = sop.replacing(with: zero, where: sop .< zero)
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var out = SIMD3<Float>(
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pow(clamped.x, power.x),
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pow(clamped.y, power.y),
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pow(clamped.z, power.z))
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// Saturation about Rec709 luma.
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if saturation != 1 {
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let luma = (out * Self.lumaWeights).sum()
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out = SIMD3(repeating: luma) + (out - SIMD3(repeating: luma)) * saturation
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}
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return out
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}
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}
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extension SIMD3 where Scalar == Float {
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public static var one: SIMD3<Float> { SIMD3(1, 1, 1) }
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}
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