我想要来自 AVCaptureVideoDataOutput 的提要中整个图像的平均像素值,我目前正在捕获图像并循环遍历像素以对它们求和。
我想知道是否有更有效的方法来使用 GPU/openGL 执行此操作,因为这是一项可并行化的图像处理任务。 (也许是严重的高斯模糊,并读取中心像素值?)
一个特定的要求是使用高水平的平均来获得高精度的结果。请注意下面的 CGFloat 结果。
当前swift 2代码:
编辑:添加了 CIAreaAverage 的实现,正如 Simon 在下面所建议的那样。它由 useGPU
bool 值分隔。
func captureOutput(captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, fromConnection connection: AVCaptureConnection!) {
var redmean:CGFloat = 0.0;
var greenmean:CGFloat = 0.0;
var bluemean:CGFloat = 0.0;
if (useGPU) {
let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)
let cameraImage = CIImage(CVPixelBuffer: pixelBuffer!)
let filter = CIFilter(name: "CIAreaAverage")
filter!.setValue(cameraImage, forKey: kCIInputImageKey)
let outputImage = filter!.valueForKey(kCIOutputImageKey) as! CIImage!
let ctx = CIContext(options:nil)
let cgImage = ctx.createCGImage(outputImage, fromRect:outputImage.extent)
let rawData:NSData = CGDataProviderCopyData(CGImageGetDataProvider(cgImage))!
let pixels = UnsafePointer<UInt8>(rawData.bytes)
let bytes = UnsafeBufferPointer<UInt8>(start:pixels, count:rawData.length)
var BGRA_index = 0
for pixel in UnsafeBufferPointer(start: bytes.baseAddress, count: bytes.count) {
switch BGRA_index {
case 0:
bluemean = CGFloat (pixel)
case 1:
greenmean = CGFloat (pixel)
case 2:
redmean = CGFloat (pixel)
case 3:
break
default:
break
}
BGRA_index++
}
} else {
let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)
CVPixelBufferLockBaseAddress(imageBuffer!, 0)
let baseAddress = CVPixelBufferGetBaseAddressOfPlane(imageBuffer!, 0)
let bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer!)
let width = CVPixelBufferGetWidth(imageBuffer!)
let height = CVPixelBufferGetHeight(imageBuffer!)
let colorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedFirst.rawValue).rawValue | CGBitmapInfo.ByteOrder32Little.rawValue
let context = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, bitmapInfo)
let imageRef = CGBitmapContextCreateImage(context)
CVPixelBufferUnlockBaseAddress(imageBuffer!, 0)
let data:NSData = CGDataProviderCopyData(CGImageGetDataProvider(imageRef))!
let pixels = UnsafePointer<UInt8>(data.bytes)
let bytes = UnsafeBufferPointer<UInt8>(start:pixels, count:data.length)
var redsum:CGFloat = 0
var greensum:CGFloat = 0
var bluesum:CGFloat = 0
var BGRA_index = 0
for pixel in UnsafeBufferPointer(start: bytes.baseAddress, count: bytes.count) {
switch BGRA_index {
case 0:
bluesum += CGFloat (pixel)
case 1:
greensum += CGFloat (pixel)
case 2:
redsum += CGFloat (pixel)
case 3:
//alphasum += UInt64(pixel)
break
default:
break
}
BGRA_index += 1
if BGRA_index == 4 { BGRA_index = 0 }
}
redmean = redsum / CGFloat(bytes.count)
greenmean = greensum / CGFloat(bytes.count)
bluemean = bluesum / CGFloat(bytes.count)
}
print("R:\(redmean) G:\(greenmean) B:\(bluemean)")
最佳答案
CIAreaAverage 过滤器性能不佳的问题和原因是缺少输入范围的定义。 因此,过滤器的输出与输入图像具有相同的大小,因此您可以遍历完整的图像而不是 1×1 像素图像。因此,执行所需的时间与您的初始版本相同。
如 CIAreaAverage 的文档中所述您可以指定一个 inputExtent 参数。 可以在 this answer 中找到如何在 swift 中完成此操作。一个类似的问题:
let cameraImage = CIImage(CVPixelBuffer: pixelBuffer!)
let extent = cameraImage.extent
let inputExtent = CIVector(x: extent.origin.x, y: extent.origin.y, z: extent.size.width, w: extent.size.height)
let filter = CIFilter(name: "CIAreaAverage", withInputParameters: [kCIInputImageKey: cameraImage, kCIInputExtentKey: inputExtent])!
let outputImage = filter.outputImage!
如果您想获得更多性能,您可以确保重用 CIContext,而不是为每个捕获的帧重新创建它。
关于ios - 计算 AVCaptureVideoDataOutput 提要的平均 RGB 像素值的最快方法 - CPU/GPU,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32732282/