43 lines
1.3 KiB
Swift
43 lines
1.3 KiB
Swift
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//
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// CGImage.swift
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// Mastodon
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//
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// Created by MainasuK Cirno on 2021-3-31.
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//
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import CoreImage
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extension CGImage {
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// Reference
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// https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.709-6-201506-I!!PDF-E.pdf
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// Luma Y = 0.2126R + 0.7152G + 0.0722B
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public var brightness: CGFloat? {
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let context = CIContext() // default with metal accelerate
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let ciImage = CIImage(cgImage: self)
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let rec709Image = context.createCGImage(
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ciImage,
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from: ciImage.extent,
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format: .RGBA8,
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colorSpace: CGColorSpace(name: CGColorSpace.itur_709) // BT.709 a.k.a Rec.709
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)
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guard let image = rec709Image,
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image.bitsPerPixel == 32,
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let data = rec709Image?.dataProvider?.data,
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let pointer = CFDataGetBytePtr(data) else { return nil }
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let length = CFDataGetLength(data)
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guard length > 0 else { return nil }
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var luma: CGFloat = 0.0
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for i in stride(from: 0, to: length, by: 4) {
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let r = pointer[i]
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let g = pointer[i + 1]
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let b = pointer[i + 2]
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let Y = 0.2126 * CGFloat(r) + 0.7152 * CGFloat(g) + 0.0722 * CGFloat(b)
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luma += Y
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}
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luma /= CGFloat(width * height)
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return luma
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}
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}
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