# vImageAlphaBlend_PlanarF(_:_:_:_:_:_:_:) Performs nonpremultiplied alpha compositing of two 8-bit planar buffers. ``` func vImageAlphaBlend_PlanarF(_ srcTop: UnsafePointer, _ srcTopAlpha: UnsafePointer, _ srcBottom: UnsafePointer, _ srcBottomAlpha: UnsafePointer, _ alpha: UnsafePointer, _ dest: UnsafePointer, _ flags: vImage_Flags) -> vImage_Error ``` ## Parameters `srcTop` The vImage buffer that provides the source top image. `srcTopAlpha` The vImage buffer that provides the source top alpha. `srcBottom` The vImage buffer that provides the source bottom image. `srcBottomAlpha` The vImage buffer that provides the source bottom alpha. `alpha` The source vImage buffer that provides the precalculated alpha values of the composite image. Precalculate these values by calling the function [`vImagePremultipliedAlphaBlend_PlanarF(_:_:_:_:_:)`](/documentation/Accelerate/vImagePremultipliedAlphaBlend_PlanarF(_:_:_:_:_:)). `dest` A pointer to the destination vImage buffer structure. You’re responsible for filling out the [`height`](/documentation/Accelerate/vImage_Buffer/height), [`width`](/documentation/Accelerate/vImage_Buffer/width), and [`rowBytes`](/documentation/Accelerate/vImage_Buffer/rowBytes) fields of this structure, and for allocating a data buffer of the appropriate size. On return, the data buffer this structure points to contains the destination image data. When you no longer need the data buffer, deallocate the memory to prevent memory leaks. `flags` The options to use when performing the operation. If your code implements its own tiling or its own multithreading, pass [`kvImageDoNotTile`](/documentation/Accelerate/kvImageDoNotTile); otherwise, pass [`kvImageNoFlags`](/documentation/Accelerate/kvImageNoFlags). ## Return Value [`kvImageNoError`](/documentation/Accelerate/kvImageNoError); otherwise, one of the error codes in . ## Discussion In order to provide the best performance, this function doesn’t calculate the alpha channel for the composite image. Use the following code to calculate the alpha channel for the composite image that you pass to this function as the `alpha` parameter: ```swift vImagePremultipliedAlphaBlend_PlanarF(srcTopAlpha, srcTopAlpha, srcBottomAlpha, alpha, vImage_Flags(kvImageNoFlags)) ``` On return of [`vImagePremultipliedAlphaBlend_Planar8(_:_:_:_:_:)`](/documentation/Accelerate/vImagePremultipliedAlphaBlend_Planar8(_:_:_:_:_:)), the value of each pixel in the alpha buffer is: ```objc float alpha = srcTopAlpha + (1.0 - srcTopAlpha) * srcBottomAlpha ``` If you’re performing an alpha blend on multiple-channel data, such as an RGB image, use the same alpha channel buffer for each call to this function. On return of this function, the value of each pixel in the destination buffer is: ```objc float destColor = ( srcTopColor * srcTopAlpha + (1.0 - srcTopAlpha) * srcBottomAlpha * srcBottomColor ) / alpha ``` ## See Also --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)