---
title: kVTCompressionPropertyKey_LogTransferFunction
framework: Video Toolbox
role: symbol
role_heading: Global Variable
platforms: [iOS 27.0+, iPadOS 27.0+, Mac Catalyst 27.0+, macOS 27.0+, tvOS 27.0+, visionOS 27.0+]
path: videotoolbox/kvtcompressionpropertykey_logtransferfunction
---

# kVTCompressionPropertyKey_LogTransferFunction

Indicates that the transfer function or gamma of the content is a log format and identifies the specific log curve. Log curve identifiers include kCVImageBufferLogTransferFunction_AppleLog (“com.apple.rec2020.apple-log”) and kCVImageBufferLogTransferFunction_AppleLog2 (“com.apple.apple-wide-gamut.apple-log”). When the LogTransferFunction is specified for a VTCompressionSession, if source image buffers do not have exactly that LogTransferFunction, encoding will fail.

## Declaration

```swift
let kVTCompressionPropertyKey_LogTransferFunction: CFString
```