如何获取YpCbCr8BiPlanar CVPixelBuffer的亮度数据

Question

我尝试获取 CVPixelBuffer 的平均亮度，但该函数在处理几行后崩溃并显示 EXC_BAD_ACCESS 消息。

我想我不明白如何使用Apple的YpCbCr8BiPlanar格式。

这是我的功能。知道我做错了什么吗？

        func averageLuminance(pixelBuffer: CVPixelBuffer) -> Float? {
            guard CVPixelBufferGetPixelFormatType(pixelBuffer) == kCVPixelFormatType_Lossy_420YpCbCr8BiPlanarFullRange else {
                print("Pixel buffer format mismatch.")
                return nil
            }
            
            CVPixelBufferLockBaseAddress(pixelBuffer, .readOnly)
            defer { CVPixelBufferUnlockBaseAddress(pixelBuffer, .readOnly) }
            
            guard let baseAddress = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 0) else {
                print("Unable to get base address.")
                return nil
            }
            
            let lumaWidth = CVPixelBufferGetWidthOfPlane(pixelBuffer, 0)
            let lumaHeight = CVPixelBufferGetHeightOfPlane(pixelBuffer, 0)
            let lumaRowBytes = CVPixelBufferGetBytesPerRowOfPlane(pixelBuffer, 0)
            
            var totalLuminance: Float = 0.0
            
            for row in 0..<lumaHeight {
                let rowBaseAddress = baseAddress.advanced(by: row * lumaRowBytes)
                let rowPointer = rowBaseAddress.assumingMemoryBound(to: UInt8.self)
                
                var rowSum: Float = 0.0
                for col in 0..<lumaWidth {
                    rowSum += Float(rowPointer[col])
                }
                
                let rowAverageLuminance = rowSum / Float(lumaWidth)
                totalLuminance += rowAverageLuminance
            }
            
            let averageLuminance = totalLuminance / Float(lumaHeight)
            
            return averageLuminance
        }

Answer 1

有损类型使用小于8bit来描述一个像素，所以我使用非压缩类型来避免这个问题