constrast enhancement for browser image

pkg/producer/enhancement.go

@@ -0,0 +1,124 @@
+package producer
+
+import (
+	"gocv.io/x/gocv"
+)
+
+const (
+	NoEnhancement                = "NoEnhancement"
+	StretchToMinimumMaximum      = "StretchToMinimumMaximum"
+	StretchToCumulativeCutMinMax = "StretchToCumulativeCutMinMax"
+)
+
+type ContrastEnhancement struct {
+	minimumValue         int
+	maximumValue         int
+	lookupTableOffset    int
+	lookupTable          []int
+	mRasterDataTypeRange int
+	enhancementType      string
+	//!< Range is [ min + cumulativeCutLower() * (max - min), min + cumulativeCutUpper() * (max - min) ]
+	cumulativeCutLower float64
+	cumulativeCutUpper float64
+}
+
+func NewContrastEnhancement(minimumValue, maximumValue int) *ContrastEnhancement {
+	ce := &ContrastEnhancement{
+		enhancementType:    StretchToMinimumMaximum,
+		cumulativeCutLower: 0,
+		cumulativeCutUpper: 1,
+	}
+	ce.minimumValue = minimumValue + int(ce.cumulativeCutLower)*(maximumValue-minimumValue)
+	ce.maximumValue = minimumValue + int(ce.cumulativeCutUpper)*(maximumValue-minimumValue)
+	ce.mRasterDataTypeRange = ce.maximumValue - ce.minimumValue
+	ce.lookupTableOffset = -1 * ce.minimumValue
+	ce.lookupTable = make([]int, ce.mRasterDataTypeRange+1)
+	ce.generateLookupTable()
+
+	return ce
+}
+
+func (ce ContrastEnhancement) enhance(value int) int {
+	if ce.enhancementType != NoEnhancement {
+		shiftedValue := value + ce.lookupTableOffset
+		if shiftedValue >= 0 && shiftedValue < ce.mRasterDataTypeRange+1 {
+			return ce.lookupTable[shiftedValue]
+		}
+		return 0
+	}
+
+	return ce.linearMinMaxEnhancement(value)
+}
+
+func (ce *ContrastEnhancement) generateLookupTable() {
+	for i := range ce.lookupTable {
+		ce.lookupTable[i] = ce.linearMinMaxEnhancement(i - ce.lookupTableOffset)
+	}
+}
+
+func (ce ContrastEnhancement) linearMinMaxEnhancement(value int) int {
+	stretchedValue := (float64(value-ce.minimumValue) / float64(ce.mRasterDataTypeRange)) * 255.0
+	if stretchedValue < 0 {
+		return 0
+	} else if stretchedValue > 255 {
+		return 255
+	}
+	return int(stretchedValue)
+}
+
+func cumulativeCountCutEnhancement(img gocv.Mat, cumulativeCutLower, cumulativeCutUpper float64) gocv.Mat {
+	dataTypeMax := 65536
+	// 计算直方图
+	hist := make([]int, dataTypeMax)
+	for y := 0; y < img.Rows(); y++ {
+		for x := 0; x < img.Cols(); x++ {
+			hist[uint16(img.GetShortAt(y, x))]++
+		}
+	}
+
+	// 计算累积直方图
+	cdf := make([]int, dataTypeMax)
+	cdf[0] = hist[0]
+	for i := 1; i < dataTypeMax; i++ {
+		cdf[i] = cdf[i-1] + hist[i]
+	}
+
+	// 计算低高阈值
+	totalPixels := img.Rows() * img.Cols()
+	lowCutoff := int(float64(totalPixels) * cumulativeCutLower)
+	highCutoff := int(float64(totalPixels) * cumulativeCutUpper)
+
+	var lowerBound, upperBound int
+	for i, v := range cdf {
+		if v > lowCutoff {
+			lowerBound = i
+			break
+		}
+	}
+	for i := dataTypeMax - 1; i >= 0; i-- {
+		if cdf[i] < highCutoff {
+			upperBound = i
+			break
+		}
+	}
+
+	// 重新映射灰度值
+	enhancedImg := gocv.NewMatWithSize(img.Rows(), img.Cols(), gocv.MatTypeCV8U)
+	for y := 0; y < img.Rows(); y++ {
+		for x := 0; x < img.Cols(); x++ {
+			oldVal := uint16(img.GetShortAt(y, x))
+			newVal := (int(oldVal) - lowerBound) * 255 / (upperBound - lowerBound)
+			if newVal > 255 {
+				newVal = 255
+			}
+			if newVal < 0 {
+				newVal = 0
+			}
+
+			enhancedImg.SetUCharAt(y, x, uint8(newVal))
+		}
+	}
+
+	return enhancedImg
+
+}