300x300像素Png图像到字节数组

Question

我的目标是从 CVImageBuffer（相机流）中提取 300x300 像素帧并将其转换为 UInt 字节数组。从技术上讲，数组大小应该是 90,000。但是，我得到了更大的价值。任何帮助将不胜感激发现错误。

将Image缓冲区转换为UIImage的方法

 func getImageFromSampleBuffer(image_buffer : CVImageBuffer?) -> UIImage?
  {
    if let imageBuffer = image_buffer {
        // Lock the base address of the pixel buffer
        CVPixelBufferLockBaseAddress(imageBuffer, CVPixelBufferLockFlags.readOnly);


        // Get the number of bytes per row for the pixel buffer
        let baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);

        // Get the number of bytes per row for the pixel buffer
        let bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
        // Get the pixel buffer width and height
        let width = CVPixelBufferGetWidth(imageBuffer);
        let height = CVPixelBufferGetHeight(imageBuffer);

        // Create a device-dependent RGB color space
        let colorSpace = CGColorSpaceCreateDeviceRGB();

        // Create a bitmap graphics context with the sample buffer data
        var bitmapInfo: UInt32 = CGBitmapInfo.byteOrder32Little.rawValue
        bitmapInfo |= CGImageAlphaInfo.premultipliedFirst.rawValue & CGBitmapInfo.alphaInfoMask.rawValue
        //let bitmapInfo: UInt32 = CGBitmapInfo.alphaInfoMask.rawValue
        let context = CGContext.init(data: baseAddress, width: width, height: height, bitsPerComponent: 8, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo)
        // Create a Quartz image from the pixel data in the bitmap graphics context
        let quartzImage = context?.makeImage();
        // Unlock the pixel buffer
        CVPixelBufferUnlockBaseAddress(imageBuffer, CVPixelBufferLockFlags.readOnly);

        // Create an image object from the Quartz image
        let image = UIImage.init(cgImage: quartzImage!);

        return (image);
    }
   return nil
  }

}

将图像数据转换为 UInt8 数组的扩展

 extension Data {
   func toByteArray() -> [UInt8]? {
    var byteData = [UInt8](repeating:0, count: self.count)
    self.copyBytes(to: &byteData, count: self.count)
    return byteData
   }
 }

代码的使用

    let image = getImageFromSampleBuffer(image_buffer: imageBuffer)

   //Issue*******
    if let byteArrayOfImage = image.copy(newSize: CGSize(width: 300, height: 300))?.pngData()?.toByteArray(){

       print(byteArrayOfImage.count) // Technically should print 90,000. However it prints a large value
    }

我错过了什么

Answer 1

你的期望Technically the array size should be 90,000可能是错误的。

1. 如果您的 CVPixelBuffer 的格式是 BRGA 或其他 4 通道类型，则数组大小将为 w*h*4=360,000，其中 w*4 或更一般地说，w*channel_count 是 row stride。

2. CVPixelBuffer 通常按 16 个字节对齐： https://developer.apple.com/documentation/corevideo/kcvpixelbufferbytesperrowalignmentkey?language=objc 所以真正的row stride可能比w*channel_count还要多。

您应该检查值bytesPerRow 以了解您的整个问题。