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# channelDescription(bufferType:)

Returns the range and clamp limits for a specified channel in a Core Video image format.

```
func channelDescription(bufferType: vImage.BufferType) -> vImageChannelDescription?
```

## Parameters

`bufferType`

The source buffer type.

## Return Value

A [`vImageChannelDescription`](/documentation/Accelerate/vImageChannelDescription) structure that describes the range and clamp limits for the specified channel.

## Discussion

Use this function to return the [`vImageChannelDescription`](/documentation/Accelerate/vImageChannelDescription) description for a specified channel in a Core Video format.

For example, the following code prints the description of each channel in a <doc://com.apple.documentation/documentation/CoreVideo/kCVPixelFormatType_420YpCbCr8Planar> Core Video image format:

```swift
let cvImageFormat = vImageCVImageFormat.make(
    format: .format420YpCbCr8Planar,
    matrix: kvImage_ARGBToYpCbCrMatrix_ITU_R_709_2.pointee,
    chromaSiting: .center,
    colorSpace: CGColorSpace(name: CGColorSpace.sRGB)!,
    alphaIsOpaqueHint: true)!

// Prints:
//    luminance   vImageChannelDescription(min: 0.0, zero: 16.0, full: 235.0, max: 255.0)
//    Cb          vImageChannelDescription(min: 0.0, zero: 128.0, full: 240.0, max: 255.0)
//    Cr          vImageChannelDescription(min: 0.0, zero: 128.0, full: 240.0, max: 255.0)
for channel in cvImageFormat.channels {
    let desc = cvImageFormat.channelDescription(bufferType: channel)!
    print("\(channel) \t\t \(desc)")
}
```

## See Also

[`func vImageCVImageFormat_CopyChannelDescription(vImageCVImageFormat, UnsafePointer<vImageChannelDescription>, vImageBufferTypeCode) -> vImage_Error`](/documentation/Accelerate/vImageCVImageFormat_CopyChannelDescription(_:_:_:))

Copies the channel description for a particular channel type to an image format.


---

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