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convolution_helpers.go
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/
convolution_helpers.go
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package rimage
import (
"errors"
"image"
"image/color"
"gonum.org/v1/gonum/mat"
)
// BorderPad is an enum type for supported padding types.
type BorderPad int
const (
//nolint:dupword
// BorderConstant - X X X A B C D E X X X - where X is a black ( color.Gray{0} ) pixel.
BorderConstant BorderPad = iota
//nolint:dupword
// BorderReplicate - A A A A B C D E E E E - copies the nearest border pixel into padding.
BorderReplicate
// BorderReflect - D C B A B C D E D C B - reflects the nearest pixel group around border pixel.
BorderReflect
)
// Paddings struct holds the padding sizes for each padding.
type Paddings struct {
// PaddingLeft is the size of the left padding
PaddingLeft int
// PaddingRight is the size of the right padding
PaddingRight int
// PaddingTop is the size of the top padding
PaddingTop int
// PaddingBottom is the size of the bottom padding
PaddingBottom int
}
func topPaddingReplicate(img image.Image, p Paddings, setPixel func(int, int, color.Color)) {
originalSize := img.Bounds().Size()
for x := p.PaddingLeft; x < originalSize.X+p.PaddingLeft; x++ {
firstPixel := img.At(x-p.PaddingLeft, p.PaddingTop)
for y := 0; y < p.PaddingTop; y++ {
setPixel(x, y, firstPixel)
}
}
}
func bottomPaddingReplicate(img image.Image, p Paddings, setPixel func(int, int, color.Color)) {
originalSize := img.Bounds().Size()
for x := p.PaddingLeft; x < originalSize.X+p.PaddingLeft; x++ {
lastPixel := img.At(x-p.PaddingLeft, originalSize.Y-1)
for y := p.PaddingTop + originalSize.Y; y < originalSize.Y+p.PaddingTop+p.PaddingBottom; y++ {
setPixel(x, y, lastPixel)
}
}
}
func leftPaddingReplicate(img, padded image.Image, p Paddings, setPixel func(int, int, color.Color)) {
originalSize := img.Bounds().Size()
for y := 0; y < originalSize.Y+p.PaddingBottom+p.PaddingTop; y++ {
firstPixel := padded.At(p.PaddingLeft, y)
for x := 0; x < p.PaddingLeft; x++ {
setPixel(x, y, firstPixel)
}
}
}
func rightPaddingReplicate(img, padded image.Image, p Paddings, setPixel func(int, int, color.Color)) {
originalSize := img.Bounds().Size()
for y := 0; y < originalSize.Y+p.PaddingBottom+p.PaddingTop; y++ {
lastPixel := padded.At(originalSize.X+p.PaddingLeft-1, y)
for x := originalSize.X + p.PaddingLeft; x < originalSize.X+p.PaddingLeft+p.PaddingRight; x++ {
setPixel(x, y, lastPixel)
}
}
}
func topPaddingReflect(img image.Image, p Paddings, setPixel func(int, int, color.Color)) {
originalSize := img.Bounds().Size()
for x := p.PaddingLeft; x < originalSize.X+p.PaddingLeft; x++ {
for y := 0; y < p.PaddingTop; y++ {
pixel := img.At(x-p.PaddingLeft, p.PaddingTop-y)
setPixel(x, y, pixel)
}
}
}
func bottomPaddingReflect(img image.Image, p Paddings, setPixel func(int, int, color.Color)) {
originalSize := img.Bounds().Size()
for x := p.PaddingLeft; x < originalSize.X+p.PaddingLeft; x++ {
for y := p.PaddingTop + originalSize.Y; y < originalSize.Y+p.PaddingTop+p.PaddingBottom; y++ {
pixel := img.At(x-p.PaddingLeft, originalSize.Y-(y-p.PaddingTop-originalSize.Y)-2)
setPixel(x, y, pixel)
}
}
}
func leftPaddingReflect(img, padded image.Image, p Paddings, setPixel func(int, int, color.Color)) {
originalSize := img.Bounds().Size()
for y := 0; y < originalSize.Y+p.PaddingBottom+p.PaddingTop; y++ {
for x := 0; x < p.PaddingLeft; x++ {
pixel := padded.At(2*p.PaddingLeft-x, y)
setPixel(x, y, pixel)
}
}
}
func rightPaddingReflect(img, padded image.Image, p Paddings, setPixel func(int, int, color.Color)) {
originalSize := img.Bounds().Size()
for y := 0; y < originalSize.Y+p.PaddingBottom+p.PaddingTop; y++ {
for x := originalSize.X + p.PaddingLeft; x < originalSize.X+p.PaddingLeft+p.PaddingRight; x++ {
pixel := padded.At(originalSize.X+p.PaddingLeft-(x-originalSize.X-p.PaddingLeft)-2, y)
setPixel(x, y, pixel)
}
}
}
// PaddingFloat64 pads a *mat.Dense - padding mode = reflect.
func PaddingFloat64(img *mat.Dense, kernelSize, anchor image.Point, border BorderPad) (*mat.Dense, error) {
h, w := img.Dims()
originalSize := image.Point{w, h}
p, err := computePaddingSizes(kernelSize, anchor)
if err != nil {
return nil, err
}
rect := getImageRectangleFromPaddingSizes(p, originalSize)
newW, newH := rect.Max.X, rect.Max.Y
padded := mat.NewDense(newH, newW, nil)
for x := p.PaddingLeft; x < originalSize.X+p.PaddingLeft; x++ {
for y := p.PaddingTop; y < originalSize.Y+p.PaddingTop; y++ {
padded.Set(y, x, img.At(y-p.PaddingTop, x-p.PaddingLeft))
}
}
return padded, nil
}
// PaddingGray appends padding to a given grayscale image. The size of the padding is calculated from the kernel size
// and the anchor point. Supported Border types are: BorderConstant, BorderReplicate, BorderReflect.
// Example of usage:
//
// res, err := padding.PaddingGray(img, {5, 5}, {1, 1}, BorderReflect)
//
// Note: this will add a 1px padding for the top and left borders of the image and a 3px padding fot the bottom and
// right borders of the image.
func PaddingGray(img *image.Gray, kernelSize, anchor image.Point, border BorderPad) (*image.Gray, error) {
originalSize := img.Bounds().Size()
p, err := computePaddingSizes(kernelSize, anchor)
if err != nil {
return nil, err
}
rect := getImageRectangleFromPaddingSizes(p, originalSize)
padded := image.NewGray(rect)
for x := p.PaddingLeft; x < originalSize.X+p.PaddingLeft; x++ {
for y := p.PaddingTop; y < originalSize.Y+p.PaddingTop; y++ {
padded.Set(x, y, img.GrayAt(x-p.PaddingLeft, y-p.PaddingTop))
}
}
switch border {
case BorderConstant:
// do nothing
case BorderReplicate:
topPaddingReplicate(img, p, func(x, y int, pixel color.Color) {
padded.Set(x, y, pixel)
})
bottomPaddingReplicate(img, p, func(x, y int, pixel color.Color) {
padded.Set(x, y, pixel)
})
leftPaddingReplicate(img, padded, p, func(x, y int, pixel color.Color) {
padded.Set(x, y, pixel)
})
rightPaddingReplicate(img, padded, p, func(x, y int, pixel color.Color) {
padded.Set(x, y, pixel)
})
case BorderReflect:
topPaddingReflect(img, p, func(x, y int, pixel color.Color) {
padded.Set(x, y, pixel)
})
bottomPaddingReflect(img, p, func(x, y int, pixel color.Color) {
padded.Set(x, y, pixel)
})
leftPaddingReflect(img, padded, p, func(x, y int, pixel color.Color) {
padded.Set(x, y, pixel)
})
rightPaddingReflect(img, padded, p, func(x, y int, pixel color.Color) {
padded.Set(x, y, pixel)
})
default:
return nil, errors.New("unknown Border type")
}
return padded, nil
}
// helper functions.
func computePaddingSizes(kernelSize, anchor image.Point) (Paddings, error) {
var p Paddings
if kernelSize.X < 0 || kernelSize.Y < 0 {
return p, errors.New("kernel size is negative")
}
if anchor.X < 0 || anchor.Y < 0 {
return p, errors.New("anchor value is negative")
}
if anchor.X > kernelSize.X || anchor.Y > kernelSize.Y {
return p, errors.New("anchor value outside of the kernel")
}
p = Paddings{
PaddingLeft: anchor.X, PaddingRight: kernelSize.X - anchor.X - 1,
PaddingTop: anchor.Y, PaddingBottom: kernelSize.Y - anchor.Y - 1,
}
return p, nil
}
func getImageRectangleFromPaddingSizes(p Paddings, imgSize image.Point) image.Rectangle {
x := p.PaddingLeft + p.PaddingRight + imgSize.X
y := p.PaddingTop + p.PaddingBottom + imgSize.Y
return image.Rect(0, 0, x, y)
}