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# vImageCVImageFormat_GetChannelDescription(_:_:)

Returns the channel description for a particular channel type.

```
func vImageCVImageFormat_GetChannelDescription(_ format: vImageConstCVImageFormat, _ type: vImageBufferTypeCode) -> UnsafePointer<vImageChannelDescription>!
```

## Parameters

`format`

The Core Video image format to query.

`type`

The type of the channel that you want information about. For example, [`kvImageBufferTypeCode_Luminance`](/documentation/Accelerate/kvImageBufferTypeCode_Luminance).

## Return Value

A pointer to a [`vImageChannelDescription`](/documentation/Accelerate/vImageChannelDescription) structure that contains the channel description.

## Discussion

The functions that create Core Video image formats, such as [`vImageCVImageFormat_CreateWithCVPixelBuffer(_:)`](/documentation/Accelerate/vImageCVImageFormat_CreateWithCVPixelBuffer(_:)), return a [`vImageCVImageFormat`](/documentation/Accelerate/vImageCVImageFormat). The following code shows how you create a [`vImageConstCVImageFormat`](/documentation/Accelerate/vImageConstCVImageFormat) representation of a [`vImageCVImageFormat`](/documentation/Accelerate/vImageCVImageFormat) instance to pass to [`vImageCVImageFormat_GetChannelDescription(_:_:)`](/documentation/Accelerate/vImageCVImageFormat_GetChannelDescription(_:_:)):

```swift
let channelDescription = withUnsafeBytes(of: cvImageFormat) { bytes in
    let format = bytes.assumingMemoryBound(
        to: vImageConstCVImageFormat.self).first!
    
    return vImageCVImageFormat_GetChannelDescription(format,
                                                     vImageBufferTypeCode(kvImageBufferTypeCode_Luminance))
}
```

## See Also

[`channelDescription(bufferType:)`](/documentation/Accelerate/vImageCVImageFormat/channelDescription(bufferType:))

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


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