# premultiply(alpha:) Transforms an 8-bit planar pixel buffer in-place from nonpremultiplied alpha format to premultiplied alpha format. ``` func premultiply(alpha: vImage.PixelBuffer) ``` ## Parameters `alpha` An 8-bit planar pixel buffer that contains the alpha. ## Discussion This function multiplies the color values in `self` by the corresponding alpha values. The function treats the values `0 ... 255` in both pixel buffers as the values `0 ... 1`. For example, the following code premultiplies a 4 x 1 planar pixel buffer with the corresponding pixels in a separate planar alpha buffer: ```swift let src = vImage.PixelBuffer( pixelValues: [32, 64, 128, 255], size: vImage.Size(width: 4, height: 1)) let alpha = vImage.PixelBuffer( pixelValues: [0, 128, 128, 255], size: vImage.Size(width: 4, height: 1)) src.premultiply(alpha: alpha) // Prints "[0, 32, 64, 255]". print(src.array) ``` --- 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)