# withBNNSTensor(_:) Calls the given closure with a pointer to a BNNS tensor that shares memory with the pixel buffer. ``` func withBNNSTensor(_ body: (BNNSTensor) throws -> R) rethrows -> R ``` ## Parameters `body` A closure with a `BNNSTensor` parameter ## Discussion Use this function to pass image data to a `BNNSGraph`. For example, the following code creates a graph that calculates the mean value of an image and apply a threshold based on the mean. ``` let context = try BNNSGraph.makeContext { builder in let src = builder.argument(name: "source", dataType: Float16.self, shape: []) let mean = src.mean(axes: [0, 1], keepDimensions: false) let thresholded = src .> mean let result = thresholded.cast(to: Float16.self) return [result] } ``` Use `withBNNSTensor()` to pass source and destination pixel buffers to the context: ``` let source = vImage.PixelBuffer(...) let destination = vImage.PixelBuffer(...) source.withBNNSTensor { src in destination.withBNNSTensor { dst in var args = [dst, src] try! context.executeFunction(arguments: &args) } } ``` On return, `destination` contains the thresholded image data. Note that the tensor that this function creates has the shape `height, width, channels count`. If you appy a slice operation to a pixel buffer back tensor, the first dimension is the height and the second dimension is the width. For example, given the following code: ``` let sourcePixels: [Float] = [ 001, 002, 003, 004, 005, 006, 007, 008, 009, 010, 011, 012, 013, 014, 015, 016, 017, 018, 019, 020, 021, 022, 023, 024, 025, 026, 027, 028, 029, 030, 031, 032, 033, 034, 035, 036, 037, 038, 039, 040, 041, 042, 043, 044, 045, 046, 047, 048, 049, 050, 051, 052, 053, 054, 055, 056, 057, 058, 059, 060 ] let source = vImage.PixelBuffer(pixelValues: sourcePixels, size: .init(width: 3, height: 5), pixelFormat: vImage.InterleavedFx4.self) let destination = vImage.PixelBuffer(size: .init(width: 2, height: 3), pixelFormat: vImage.InterleavedFx4.self) let context = try BNNSGraph.makeContext { builder in let src = builder.argument(name: "source", dataType: Float.self, shape: [ -1, -1, -1]) let result = src[ 0...2, // rows 0, 1, 2 1...2, // cols 1, 2 0...3 ] // channels 0, 1, 2, 3 return [result] } source.withBNNSTensor { src in destination.withBNNSTensor { dst in var args = [dst, src] try! context.executeFunction(arguments: &args) } } ``` The slice selects rows 0, 1, and 2 and columns 1 and 2. On return, `destination` contains the following values: ``` [ 005, 006, 007, 008, 009, 010, 011, 012, 017, 018, 019, 020, 021, 022, 023, 024, 029, 030, 031, 032, 033, 034, 035, 036, ] ``` - Returns The return value, if any, of the body closure parameter. --- 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)