.TH "<MPSNNPadding >" 3 "Mon Jul 9 2018" "Version MetalPerformanceShaders-119.3" "MetalPerformanceShaders.framework" \" -*- nroff -*-
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.SH NAME
<MPSNNPadding >
.SH SYNOPSIS
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\fC#import <MPSNeuralNetworkTypes\&.h>\fP
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Inherits <NSObject>, and <NSSecureCoding>\&.
.SS "Instance Methods"

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.RI "(\fBMPSNNPaddingMethod\fP) \- \fBpaddingMethod\fP"
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.RI "(NSString *__nonnull) \- \fBlabel\fP"
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.RI "(\fBMPSImageDescriptor\fP *__nonnull) \- \fBdestinationImageDescriptorForSourceImages:sourceStates:forKernel:suggestedDescriptor:\fP"
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.RI "(instancetype __nullable) \- \fBinverse\fP"
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.SH "Method Documentation"
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.SS "\- (\fBMPSImageDescriptor\fP * __nonnull \fBMPSNNPadding\fP) destinationImageDescriptorForSourceImages: (NSArray< \fBMPSImage\fP * > *__nonnull) sourceImages(NSArray< \fBMPSState\fP * > *__nullable) sourceStates(\fBMPSKernel\fP *__nonnull) kernel(\fBMPSImageDescriptor\fP *__nonnull) inDescriptor\fC [optional]\fP"
Determine padding and sizing of result images  \fBA\fP MPSNNPaddingMethod must both return a valid \fBMPSImageDescriptor\fP and set the MPSKernel\&.offset to the correct value\&. This is a required feature if the MPSNNPaddingMethodCustom bit is set in the paddingMethod\&.
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Some code that may prove helpful:
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.nf
const int centeringPolicy = 0;  // When kernelSize is even: 0 pad bottom right\&. 1 pad top left\&.    Centers the kernel for even sized kernels\&.

typedef enum Style{
    StyleValidOnly = -1,
    StyleSame = 0,
    StyleFull = 1
}Style;

// Typical destination size in one dimension for forward filters (most filters)
static int DestSize( int sourceSize, int stride, int filterWindowSize, Style style ){
    sourceSize += style * (filterWindowSize - 1);       // adjust how many pixels we are allowed to read
    return (sourceSize + stride - 1) / stride;          // sourceSize / stride, round up
}

// Typical destination size in one dimension for reverse filters (e\&.g\&. convolution transpose)
static int DestSizeReverse( int sourceSize, int stride, int filterWindowSize, Style style ){
    return (sourceSize-1) * stride +        // center tap for the last N-1 results\&. Take stride into account
            1 +                             // center tap for the first result
            style * (filterWindowSize-1);   // add or subtract (or ignore) the filter extent
}

// Find the MPSOffset in one dimension
static int Offset( int sourceSize, int stride, int filterWindowSize, Style style ){
    // The correction needed to adjust from position of left edge to center per MPSOffset definition
    int correction = filterWindowSize / 2;

    // exit if all we want is to start consuming pixels at the left edge of the image\&.
    if( 0 )
        return correction;

    // Center the area consumed in the source image:
    // Calculate the size of the destination image
    int destSize = DestSize( sourceSize, stride, filterWindowSize, style ); // use DestSizeReverse here instead as appropriate

    // calculate extent of pixels we need to read in source to populate the destination
    int readSize = (destSize-1) * stride + filterWindowSize;

    // calculate number of missing pixels in source
    int extraSize = readSize - sourceSize;

    // number of missing pixels on left side
    int leftExtraPixels = (extraSize + centeringPolicy) / 2;

    // account for the fact that the offset is based on the center pixel, not the left edge
    return correction - leftExtraPixels;
}
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\fBParameters:\fP
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\fIsourceImages\fP The list of source images to be used 
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\fIsourceStates\fP The list of source states to be used 
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\fIkernel\fP The \fBMPSKernel\fP the padding method will be applied to\&. Set the kernel\&.offset 
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\fIinDescriptor\fP MPS will prepare a starting guess based on the padding policy (exclusive of MPSNNPaddingMethodCustom) set for the object\&. You should adjust the offset and image size accordingly\&. It is on an autoreleasepool\&.
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\fBReturns:\fP
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The \fBMPSImageDescriptor\fP to use to make a \fBMPSImage\fP to capture the results from the filter\&. The \fBMPSImageDescriptor\fP is assumed to be on an autoreleasepool\&. Your method must also set the kernel\&.offset property\&. 
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.SS "\- (instancetype __nullable \fBMPSNNPadding\fP) inverse \fC [optional]\fP"
Make a 'inverted' padding policy suitable for a training gradient pass\&. 
.SS "\- (NSString*__nonnull \fBMPSNNPadding\fP) label \fC [optional]\fP"
\fBA\fP human readable string that describes the padding policy\&. Useful for verbose debugging support\&. 
.SS "\- (\fBMPSNNPaddingMethod\fP \fBMPSNNPadding\fP) paddingMethod \fC [required]\fP"
Get the preferred padding method for the node 

.SH "Author"
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Generated automatically by Doxygen for MetalPerformanceShaders\&.framework from the source code\&.