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threshold.go
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threshold.go
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package threshold
import (
"errors"
"github.com/danhab99/Imger/histogram"
"github.com/danhab99/Imger/utils"
"image"
"image/color"
)
// Method is an enum type for global threshold methods
type Method int
const (
// ThreshBinary
// _
// | maxVal if src(x, y) > thresh
// dst(x, y) = |
// | 0 otherwise
// |_
ThreshBinary Method = iota
// ThreshBinaryInv
// _
// | 0 if src(x, y) > thresh
// dst(x, y) = |
// | maxVal otherwise
// |_
ThreshBinaryInv
// ThreshTrunc
// _
// | thresh if src(x, y) > thresh
// dst(x, y) = |
// | src(x, y) otherwise
// |_
ThreshTrunc
// ThreshToZero
// _
// | src(x, y) if src(x, y) > thresh
// dst(x, y) = |
// | 0 otherwise
// |_
ThreshToZero
// ThreshToZeroInv
// _
// | 0 if src(x, y) > thresh
// dst(x, y) = |
// | src(x, y) otherwise
// |_
ThreshToZeroInv
)
// Threshold returns a 8 bit grayscale image as result which was segmented using one of the following methods:
// ThreshBinary, ThreshBinaryInv, ThreshTrunc, ThreshToZero, ThreshToZeroInv
func Threshold(img *image.Gray, t uint8, method Method) (*image.Gray, error) {
var setPixel func(*image.Gray, int, int)
switch method {
case ThreshBinary:
setPixel = func(gray *image.Gray, x int, y int) {
pixel := img.GrayAt(x, y).Y
if pixel < t {
gray.SetGray(x, y, color.Gray{Y: utils.MinUint8})
} else {
gray.SetGray(x, y, color.Gray{Y: utils.MaxUint8})
}
}
case ThreshBinaryInv:
setPixel = func(gray *image.Gray, x int, y int) {
pixel := img.GrayAt(x, y).Y
if pixel < t {
gray.SetGray(x, y, color.Gray{Y: utils.MaxUint8})
} else {
gray.SetGray(x, y, color.Gray{Y: utils.MinUint8})
}
}
case ThreshTrunc:
{
setPixel = func(gray *image.Gray, x int, y int) {
pixel := img.GrayAt(x, y).Y
if pixel < t {
gray.SetGray(x, y, color.Gray{Y: pixel})
} else {
gray.SetGray(x, y, color.Gray{Y: t})
}
}
}
case ThreshToZero:
setPixel = func(gray *image.Gray, x int, y int) {
pixel := img.GrayAt(x, y).Y
if pixel < t {
gray.SetGray(x, y, color.Gray{Y: utils.MinUint8})
} else {
gray.SetGray(x, y, color.Gray{Y: pixel})
}
}
case ThreshToZeroInv:
setPixel = func(gray *image.Gray, x int, y int) {
pixel := img.GrayAt(x, y).Y
if pixel < t {
gray.SetGray(x, y, color.Gray{Y: pixel})
} else {
gray.SetGray(x, y, color.Gray{Y: utils.MinUint8})
}
}
default:
return nil, errors.New("invalid threshold method")
}
return threshold(img, setPixel), nil
}
// Threshold16 returns a grayscale image represented on 16 bits as result which was segmented using one of the following
// Methods: ThreshBinary, ThreshBinaryInv, ThreshTrunc, ThreshToZero, ThreshToZeroInv
func Threshold16(img *image.Gray16, t uint16, method Method) (*image.Gray16, error) {
var setPixel func(*image.Gray16, int, int)
switch method {
case ThreshBinary:
setPixel = func(gray *image.Gray16, x int, y int) {
pixel := img.Gray16At(x, y).Y
if pixel < t {
gray.SetGray16(x, y, color.Gray16{Y: utils.MinUint16})
} else {
gray.SetGray16(x, y, color.Gray16{Y: utils.MaxUint16})
}
}
case ThreshBinaryInv:
setPixel = func(gray *image.Gray16, x int, y int) {
pixel := img.Gray16At(x, y).Y
if pixel < t {
gray.SetGray16(x, y, color.Gray16{Y: utils.MaxUint16})
} else {
gray.SetGray16(x, y, color.Gray16{Y: utils.MinUint16})
}
}
case ThreshTrunc:
{
setPixel = func(gray *image.Gray16, x int, y int) {
pixel := img.Gray16At(x, y).Y
if pixel < t {
gray.SetGray16(x, y, color.Gray16{Y: pixel})
} else {
gray.SetGray16(x, y, color.Gray16{Y: t})
}
}
}
case ThreshToZero:
setPixel = func(gray *image.Gray16, x int, y int) {
pixel := img.Gray16At(x, y).Y
if pixel < t {
gray.SetGray16(x, y, color.Gray16{Y: utils.MinUint16})
} else {
gray.SetGray16(x, y, color.Gray16{Y: pixel})
}
}
case ThreshToZeroInv:
setPixel = func(gray *image.Gray16, x int, y int) {
pixel := img.Gray16At(x, y).Y
if pixel < t {
gray.SetGray16(x, y, color.Gray16{pixel})
} else {
gray.SetGray16(x, y, color.Gray16{Y: utils.MinUint16})
}
}
default:
return nil, errors.New("invalid threshold method")
}
return threshold16(img, setPixel), nil
}
// OtsuThreshold returns a grayscale image which was segmented using Otsu's adaptive thresholding method.
// Methods: ThreshBinary, ThreshBinaryInv, ThreshTrunc, ThreshToZero, ThreshToZeroInv
// More info about Otsu's method: https://en.wikipedia.org/wiki/Otsu%27s_method
func OtsuThreshold(img *image.Gray, method Method) (*image.Gray, error) {
return Threshold(img, otsuThresholdValue(img), method)
}
// -------------------------------------------------------------------------------------------------------
func threshold(img *image.Gray, setPixel func(*image.Gray, int, int)) *image.Gray {
size := img.Bounds().Size()
gray := image.NewGray(img.Bounds())
utils.ParallelForEachPixel(size, func(x, y int) {
setPixel(gray, x, y)
})
return gray
}
func threshold16(img *image.Gray16, setPixel16 func(*image.Gray16, int, int)) *image.Gray16 {
size := img.Bounds().Size()
gray := image.NewGray16(img.Bounds())
utils.ParallelForEachPixel(size, func(x, y int) {
setPixel16(gray, x, y)
})
return gray
}
func otsuThresholdValue(img *image.Gray) uint8 {
hist := histogram.HistogramGray(img)
size := img.Bounds().Size()
totalNumberOfPixels := size.X * size.Y
var sumHist float64
for i, bin := range hist {
sumHist += float64(uint64(i) * bin)
}
var sumBackground float64
var weightBackground int
var weightForeground int
maxVariance := 0.0
var thresh uint8
for i, bin := range hist {
weightBackground += int(bin)
if weightBackground == 0 {
continue
}
weightForeground = totalNumberOfPixels - weightBackground
if weightForeground == 0 {
break
}
sumBackground += float64(uint64(i) * bin)
meanBackground := float64(sumBackground) / float64(weightBackground)
meanForeground := (sumHist - sumBackground) / float64(weightForeground)
variance := float64(weightBackground) * float64(weightForeground) * (meanBackground - meanForeground) * (meanBackground - meanForeground)
if variance > maxVariance {
maxVariance = variance
thresh = uint8(i)
}
}
return thresh
}