init(cgImage:cgImageFormat:pixelFormat:)

Declaration

init(cgImage: CGImage, cgImageFormat: inout vImage_CGImageFormat, pixelFormat: Format.Type = Format.self) throws

Parameters

• cgImage:

  The source image.

• cgImageFormat:

  The format of the image. Pass an empty Vimage_cgimageformat to specify that the function populates cgImageFormat with the properties of the image. Pass a populated Vimage_cgimageformat to specify that the function converts the image data to the format you specify.

• pixelFormat:

  The pixel format of the initialized buffer.

Mentioned in

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

Discussion

For example, the following code creates a single-channel, 8-bit per pixel buffer from a CGImage of unknown bit depth.

When you pass a populated cgImageFormat, the init(cgImage:cgImageFormat:pixelFormat:) initializer performs the conversion from the CGImage instance’s format to the vImage_CGImageFormat that you specify.

Note the bitsPerComponent, bitsPerPixel, colorSpace, and bitmapInfo.

 let cgImage = [ ... ]

 let pixelFormat = vImage.Planar8.self

 var imageFormat = vImage_CGImageFormat(
     bitsPerComponent: pixelFormat.bitsPerComponent, // 8
     bitsPerPixel: pixelFormat.bitsPerPixel,         // 8
     colorSpace: CGColorSpaceCreateDeviceGray(),
     bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue))!

 let buffer = vImage.PixelBuffer(
    cgImage: cgImage,
    cgImageFormat: &imageFormat,
    pixelFormat: pixelFormat)

The following code shows a similar workflow, but it creates a 32-bit per channel RGBA buffer:

 let cgImage = [ ... ]

 let pixelFormat = vImage.InterleavedFx4.self

 var imageFormat = vImage_CGImageFormat(
     bitsPerComponent: pixelFormat.bitsPerComponent, // 32
     bitsPerPixel: pixelFormat.bitsPerPixel,         // 32 * 4
     colorSpace: CGColorSpaceCreateDeviceRGB(),
     bitmapInfo: CGBitmapInfo(rawValue:
                                 kCGBitmapByteOrder32Host.rawValue |
                                 CGBitmapInfo.floatComponents.rawValue |
                                 CGImageAlphaInfo.noneSkipLast.rawValue))

 let buffer = vImage.PixelBuffer(
     cgImage: cgImage,
     cgImageFormat: &imageFormat,
     pixelFormat: pixelFormat)

If you pass an empty cgImageFormat, the init(cgImage:cgImageFormat:pixelFormat:) initializer populates the vImage_CGImageFormat with the properties of the CGImage instance. For example, the following code initializes a pixel buffer from a 8-bit-per-channel, 4-channel RGB image:

let cgImage = [ ... ]

var cgImageFormat = vImage_CGImageFormat()

let buffer = try vImage.PixelBuffer(
    cgImage: cgImage,
    cgImageFormat: &cgImageFormat,
    pixelFormat: vImage.Interleaved8x4.self)

// Prints "8  32  1 (`CGColorSpaceModel.rgb.rawValue`)".
print(cgImageFormat.bitsPerComponent,
      cgImageFormat.bitsPerPixel,
      cgImageFormat.colorSpace.takeRetainedValue().model.rawValue)