MPSImageConvolution(3)
NAME
MPSImageConvolution
SYNOPSIS
#import <MPSImageConvolution.h>
Inherits MPSUnaryImageKernel.
Instance Methods
(nonnull instancetype) -
initWithDevice:kernelWidth:kernelHeight:weights:
(nullable instancetype) - initWithCoder:device:
Properties
NSUInteger kernelHeight
NSUInteger kernelWidth
float bias
Additional Inherited Members
Detailed Description
MPSImageConvolution.h MetalPerformanceShaders
Copyright:
Copyright (c) 2015 Apple Inc. All rights reserved.
MetalPerformanceShaders Convolution Filters
The MPSImageConvolution convolves an image with given filter of odd
width and height. The center of the kernel aligns with the
MPSImageConvolution.offset. That is, the position of the top left
corner of the area covered by the kernel is given by
MPSImageConvolution.offset - {kernel_width>>1, kernel_height>>1, 0}
Optimized cases include 3x3,5x5,7x7,9x9,11x11, 1xN and Nx1. If a
convolution kernel does not fall into one of these cases but is a
rank-1 matrix (a.k.a. separable) then it will fall on an optimzied
separable path. Other convolutions will execute with full MxN
complexity.
If there are multiple channels in the source image, each channel is
processed independently.
Separable convolution filters 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:
-1 0 1
-2 0 2
-1 0 1
can be separated into the product of two vectors:
1
2 x [-1 0 1]
1
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.
Method Documentation
- (nullable instancetype) initWithCoder: (NSCoder *__nonnull)
aDecoder(nonnull id< MTLDevice >) device
NSSecureCoding compatability While the standard
NSSecureCoding/NSCoding method -initWithCoder: should work, since the
file can't know which device your data is allocated on, we have to
guess and may guess incorrectly. To avoid that problem, use
initWithCoder:device instead.
Parameters:
aDecoder The NSCoder subclass with your serialized MPSKernel
device The MTLDevice on which to make the MPSKernel
Returns:
A new MPSKernel object, or nil if failure.
Reimplemented from MPSUnaryImageKernel.
- (nonnull instancetype) initWithDevice: (nonnull id< MTLDevice >)
device(NSUInteger) kernelWidth(NSUInteger) kernelHeight(const float
*__nonnull) kernelWeights
Initialize a convolution filter
Parameters:
device The device the filter will run on
kernelWidth the width of the kernel
kernelHeight the height of the kernel
kernelWeights A pointer to an array of kernelWidth * kernelHeight
values to be used as the kernel. These are in row major order.
Returns:
A valid MPSImageConvolution object or nil, if failure.
Property Documentation
- bias [read], [write], [nonatomic], [assign]
The bias is a value to be added to convolved pixel before it is
converted back to the storage format. It can be used to convert
negative values into a representable range for a unsigned
MTLPixelFormat. For example, many edge detection filters produce
results in the range [-k,k]. By scaling the filter weights by 0.5/k and
adding 0.5, the results will be in range [0,1] suitable for use with
unorm formats. It can be used in combination with renormalization of
the filter weights to do video ranging as part of the convolution
effect. It can also just be used to increase the brightness of the
image.
Default value is 0.0f.
- kernelHeight [read], [nonatomic], [assign]
The height of the filter window. Must be an odd number.
- kernelWidth [read], [nonatomic], [assign]
The width of the filter window. Must be an odd number.
Author
Generated automatically by Doxygen for
MetalPerformanceShaders.framework from the source code.
Version MetalPerformanceShaders-Thu2Jul 13 2017 MPSImageConvolution(3)
Mac OS X 10.13.1 - Generated Tue Nov 7 06:10:59 CST 2017
