如何将分离出的RGB单通道生成为对应颜色的CGImage？

要实现类似图像编辑软件里的分离通道显示效果（红/绿/蓝通道分别以对应色彩显示），必须补全缺失的颜色通道——因为单通道数据默认对应灰度颜色空间，CGImage无法直接将灰度图指定为某一个RGB通道来显示色彩。以下是两种高效实现方案：

方案一：补全通道后构建RGB格式CGImage #

这是最直接的方式，通过填充其他通道为0，将单通道数据扩展为RGB格式图像：

• 红色通道：保留你的R通道数据，将G、B通道全部填充为0，合并为RGB格式后生成CGImage
• 绿色通道：保留G通道数据，R、B通道填充为0
• 蓝色通道：保留B通道数据，R、G通道填充为0

利用vImage可以高效完成通道合并，示例代码（Swift）：

import Accelerate
import CoreGraphics

func createColoredChannelImage(from channelBuffer: vImage_Buffer, channel: RGBChannel, size: CGSize) -> CGImage? {
    // 创建全0的辅助通道Buffer
    guard let zeroBuffer = try? vImage_Buffer(width: Int(size.width), height: Int(size.height), bitsPerPixel: 8) else {
        return nil
    }
    defer { zeroBuffer.free() }
    memset(zeroBuffer.data, 0, zeroBuffer.rowBytes * zeroBuffer.height)
    
    // 按目标通道排序源Buffer
    let sourceBuffers: [vImage_Buffer]
    switch channel {
    case .red:
        sourceBuffers = [channelBuffer, zeroBuffer, zeroBuffer]
    case .green:
        sourceBuffers = [zeroBuffer, channelBuffer, zeroBuffer]
    case .blue:
        sourceBuffers = [zeroBuffer, zeroBuffer, channelBuffer]
    }
    
    // 创建交错式RGB Buffer
    guard let interleavedBuffer = try? vImage_Buffer(width: Int(size.width), height: Int(size.height), bitsPerPixel: 24) else {
        return nil
    }
    defer { interleavedBuffer.free() }
    
    // 平面转交错格式
    let error = vImageConvert_PlanarToInterleaved_ARGB8888(&sourceBuffers, &interleavedBuffer, 0, UInt32(size.height), 0, 0)
    guard error == kvImageNoError else { return nil }
    
    // 生成CGImage
    let dataProvider = CGDataProvider(data: Data(bytesNoCopy: interleavedBuffer.data,
                                                 count: interleavedBuffer.rowBytes * interleavedBuffer.height,
                                                 deallocator: .free))!
    return CGImage(width: Int(size.width),
                   height: Int(size.height),
                   bitsPerComponent: 8,
                   bitsPerPixel: 24,
                   bytesPerRow: interleavedBuffer.rowBytes,
                   space: CGColorSpaceCreateDeviceRGB(),
                   bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue),
                   provider: dataProvider,
                   decode: nil,
                   shouldInterpolate: false,
                   intent: .defaultIntent)
}

enum RGBChannel {
    case red, green, blue
}

方案二：Core Image滤镜实时着色（内存更高效） #

如果不想额外占用内存存储全0通道数据，可以直接用Core Image滤镜给生成的单通道灰度图着色，无需修改原始通道数据：

• 用CIColorMonochrome滤镜，将灰度图的亮度映射到目标颜色的亮度，直接生成带色彩的通道图

示例代码（Swift）：

import CoreImage
import UIKit

func tintChannelGrayscaleImage(_ grayscaleCGImage: CGImage, targetColor: UIColor) -> CGImage? {
    let ciImage = CIImage(cgImage: grayscaleCGImage)
    guard let colorFilter = CIFilter(name: "CIColorMonochrome") else {
        return nil
    }
    
    colorFilter.setValue(ciImage, forKey: kCIInputImageKey)
    colorFilter.setValue(CIColor(color: targetColor), forKey: kCIInputColorKey)
    colorFilter.setValue(1.0, forKey: kCIInputIntensityKey)
    
    guard let outputCI = colorFilter.outputImage else { return nil }
    let ciContext = CIContext(options: [.useSoftwareRenderer: false])
    return ciContext.createCGImage(outputCI, from: outputCI.extent)
}

// 使用示例：将红色通道的灰度图转为红色调图像
// if let redGrayscaleImg = yourRedChannelGrayscaleCGImage {
//     let redColoredImg = tintChannelGrayscaleImage(redGrayscaleImg, targetColor: .red)
// }

内容的提问来源于stack exchange，提问作者God of Biscuits