BGRA to BGR convertion

CIImage_CVPixelBuffer.swift

import Foundation
import UIKit

extension CGImage {
  public var cvPixelBuffer: CVPixelBuffer? {
    let attrs = [
                  kCVPixelBufferCGImageCompatibilityKey: kCFBooleanTrue,
                  kCVPixelBufferCGBitmapContextCompatibilityKey: kCFBooleanTrue,
                  kCVPixelBufferMetalCompatibilityKey: kCFBooleanTrue
                ] as CFDictionary

    var pixelBuffer: CVPixelBuffer?
    let status = CVPixelBufferCreate(kCFAllocatorDefault,
                                     Int(self.width),
                                     Int(self.height),
                                     kCVPixelFormatType_32BGRA,
                                     attrs,
                                     &pixelBuffer)

    guard status == kCVReturnSuccess else {
      return nil
    }

    CVPixelBufferLockBaseAddress(pixelBuffer!, CVPixelBufferLockFlags.init(rawValue: 0))

    let data          = CVPixelBufferGetBaseAddress(pixelBuffer!)
    let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
    let bitmapInfo    = CGBitmapInfo(rawValue: CGBitmapInfo.byteOrder32Little.rawValue | CGImageAlphaInfo.premultipliedFirst.rawValue)
    let context       = CGContext(data: data,
                                  width: Int(self.width),
                                  height: Int(self.height),
                                  bitsPerComponent: 8,
                                  bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer!),
                                  space: rgbColorSpace,
                                  bitmapInfo: bitmapInfo.rawValue)

    context?.draw(self, in: CGRect(x: 0, y: 0, width: self.width, height: self.height))

    CVPixelBufferUnlockBaseAddress(pixelBuffer!, CVPixelBufferLockFlags(rawValue: 0))
    return pixelBuffer
  }
}

convertion.swift

import UIKit
import Accelerate

let image = UIImage(named: "File")!

let cgImage       = image.cgImage!
let cvPixelBuffer = cgImage.cvPixelBuffer!

var bgraSourceFormat = vImage_CGImageFormat(
  bitsPerComponent: 8,
  bitsPerPixel: 32,
  colorSpace: Unmanaged.passRetained(CGColorSpaceCreateDeviceRGB()),
  bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.last.rawValue),
  version: 0,
  decode: nil,
  renderingIntent: .defaultIntent
)

var bgrDestinationFormat = vImage_CGImageFormat(
  bitsPerComponent: 8,
  bitsPerPixel: 24,
  colorSpace: nil,
  bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue),
  version: 0,
  decode: nil,
  renderingIntent: .defaultIntent
)

let bgraToRgbConverter = vImageConverter_CreateWithCGImageFormat(
  &bgraSourceFormat,
  &bgrDestinationFormat,
  nil,
  vImage_Flags(kvImagePrintDiagnosticsToConsole),
  nil
)
let converter          = bgraToRgbConverter!.takeRetainedValue()

var bgraBuffer  = vImage_Buffer()
let imageFormat = vImageCVImageFormat_CreateWithCVPixelBuffer(cvPixelBuffer).takeRetainedValue()
vImageCVImageFormat_SetColorSpace(imageFormat, CGColorSpaceCreateDeviceRGB())
vImageBuffer_InitWithCVPixelBuffer(
  &bgraBuffer,
  &bgraSourceFormat,
  cvPixelBuffer,
  imageFormat,
  nil,
  vImage_Flags(kvImageNoFlags)
)

var bgrBuffer = vImage_Buffer()
vImageBuffer_Init(
  &bgrBuffer,
  bgraBuffer.height,
  bgraBuffer.width,
  bgrDestinationFormat.bitsPerPixel,
  vImage_Flags(kvImageNoFlags)
)

vImageConvert_AnyToAny(
  converter,
  &bgraBuffer,
  &bgrBuffer,
  nil,
  vImage_Flags(kvImagePrintDiagnosticsToConsole))

let bgraData = bgraBuffer.data!.assumingMemoryBound(to: UInt8.self)
let bgrData  = bgrBuffer.data!.assumingMemoryBound(to: UInt8.self)

print(bgraData[0], bgraData[1], bgraData[2], bgraData[3])
print(bgrData[0], bgrData[1], bgrData[2])

print(bgraData[4], bgraData[5], bgraData[6], bgraData[7])
print(bgrData[3], bgrData[4], bgrData[5])
print("")
print(bgrBuffer.width, bgrBuffer.height, bgrBuffer.rowBytes)