# MPSImageConvolution A filter that convolves an image with a given kernel of odd width and height. ``` class MPSImageConvolution ``` ## Overview Filter width and height can be either 3, 5, 7 or 9. If there are multiple channels in the source image, each channel is processed independently. A *separable* convolution filter may perform better when done in two passes. . A convolution filter is separable if the ratio of filter values between all rows is constant over the whole row. For example, this edge detection filter:  Can instead be separated into the product of two vectors, like so:  And consequently can be done as two, one-dimensional convolution passes back to back on the same image. In this way, the number of multiplies (ignoring the fact that we could skip zeros here) is reduced from `3*3=9` to `3+3=6`. There are similar savings for addition. For large filters, the savings can be profound. ## Topics ### Initializers [`- initWithCoder:device:`](/documentation/MetalPerformanceShaders/MPSImageConvolution/init(coder:device:)) ### Methods [`- initWithDevice:kernelWidth:kernelHeight:weights:`](/documentation/MetalPerformanceShaders/MPSImageConvolution/init(device:kernelWidth:kernelHeight:weights:)) Initializes a convolution filter. ### Properties [`kernelHeight`](/documentation/MetalPerformanceShaders/MPSImageConvolution/kernelHeight) The height of the filter window. Must be an odd number. [`kernelWidth`](/documentation/MetalPerformanceShaders/MPSImageConvolution/kernelWidth) The width of the filter window. Must be an odd number. [`bias`](/documentation/MetalPerformanceShaders/MPSImageConvolution/bias) The value added to a convolved pixel before it is converted back to its intended storage format. ## Relationships ### Conforms To [`NSSecureCoding`](/documentation/Foundation/NSSecureCoding) [`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol) [`Equatable`](/documentation/Swift/Equatable) [`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible) [`NSCoding`](/documentation/Foundation/NSCoding) [`CVarArg`](/documentation/Swift/CVarArg) [`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible) [`Hashable`](/documentation/Swift/Hashable) [`NSCopying`](/documentation/Foundation/NSCopying) ### Inherits From [`MPSUnaryImageKernel`](/documentation/MetalPerformanceShaders/MPSUnaryImageKernel) --- 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)