vImageBuffer_InitWithCGImage(_:_:_:_:_:)

Declaration

func vImageBuffer_InitWithCGImage(_ buf: UnsafeMutablePointer<vImage_Buffer>, _ format: UnsafeMutablePointer<vImage_CGImageFormat>, _ backgroundColor: UnsafePointer<CGFloat>!, _ image: CGImage, _ flags: vImage_Flags) -> vImage_Error

Parameters

• buf:

  The destination vImage buffer. On output, an initialized buffer with all fields populated.

• format:

  A Vimage_cgimageformat structure. Pass an empty structure to specify that the function populates the format with the properties of the Core Graphics image. Pass a populated structure to specify that the function converts the Core Graphics image to the format.

• backgroundColor:

  If the source image contains alpha information and the format doesn’t contain alpha information, this function flattens the source image against this parameter.

• image:

  The source Core Graphics image.

• flags:

  The options to use when performing the operation. Pass Kvimagenoallocate if the destination buffer references existing data; otherwise, pass Kvimagenoflags.

Mentioned in

• Converting bitmap data between Core Graphics images and vImage buffers
• Optimizing image-processing performance

Return Value

kvImageNoError; otherwise, one of the error codes in Data Types and Constants.

Discussion

The following code shows a passthrough function that accepts a CGImage image, populates a vImage buffer from the image, and generates a CGImage image from the buffer.

In this example, the call to vImageBuffer_InitWithCGImage(_:_:_:_:_:) populates the vImage_CGImageFormat and the vImage_Buffer variables with the properties of the source image:

static func passThrough(sourceImage: CGImage) -> CGImage? {

    var format = vImage_CGImageFormat()
    var buffer = vImage_Buffer()
    
    defer {
        buffer.free()
    }

    vImageBuffer_InitWithCGImage(
        &buffer,
        &format,
        nil,
        sourceImage,
        vImage_Flags(kvImageNoFlags))
   
    // Perform image-processing operations on `buffer`.

    let destinationCGImage = vImageCreateCGImageFromBuffer(
        &buffer,
        &format,
        nil,
        nil,
        vImage_Flags(kvImageNoFlags),
        nil)
    
    return destinationCGImage?.takeRetainedValue()
}

Pass a fully initialized vImage_CGImageFormat to specify that vImageBuffer_InitWithCGImage(_:_:_:_:_:) converts the source CGImage image to the format that format describes. The following example converts the source image to a three-channel, 8-bit-per-channel RGB image:

static func passThrough(sourceImage: CGImage) -> CGImage? {
    
    var format = vImage_CGImageFormat(
        bitsPerComponent: 8,
        bitsPerPixel: 8 * 3,
        colorSpace: CGColorSpaceCreateDeviceRGB(),
        bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue),
        renderingIntent: .defaultIntent)!

    var buffer = vImage_Buffer()

    defer {
        buffer.free()
    }
    
    vImageBuffer_InitWithCGImage(
        &buffer,
        &format,
        nil,
        sourceImage,
        vImage_Flags(kvImageNoFlags))
    
    // Perform image-processing operations on RGB888 `buffer`.

    let destinationCGImage = vImageCreateCGImageFromBuffer(
        &buffer,
        &format,
        nil,
        nil,
        vImage_Flags(kvImageNoFlags),
        nil)
    
    return destinationCGImage?.takeRetainedValue()
}