From d87bfec123f6c2fda73073998843441690995284 Mon Sep 17 00:00:00 2001
From: servostar <sven.vogel123@web.de>
Date: Tue, 4 Feb 2025 21:19:33 +0100
Subject: [PATCH] feat: exercise 2

---
 src/HistogramManipulation.py | 148 ++++++++++++++++++++++++++++++++++-
 1 file changed, 147 insertions(+), 1 deletion(-)

diff --git a/src/HistogramManipulation.py b/src/HistogramManipulation.py
index b39544c..0b96209 100755
--- a/src/HistogramManipulation.py
+++ b/src/HistogramManipulation.py
@@ -1,12 +1,23 @@
 import cv2
 import numpy as np
 import Utilities
+import math
 
+MAX_LUM_VALUES = 256
 
 # Task 1
 # function to stretch an image
 def stretchHistogram(img):
     result = img.copy()
+
+    grayscale = getLuminance(img)
+    hist = calculateHistogram(grayscale, MAX_LUM_VALUES)
+    minPos, maxPos = findMinMaxPos(hist)
+
+    for x in range(0, img.shape[0]):
+        for y in range(0, img.shape[1]):
+            result[x][y] = (grayscale[x][y] - minPos) / (maxPos - minPos) * 255.0
+
     return result
 
 
@@ -14,6 +25,25 @@ def stretchHistogram(img):
 # function to equalize an image
 def equalizeHistogram(img):
     result = img.copy()
+
+    grayscale = getLuminance(img)
+    hist = calculateHistogram(grayscale, MAX_LUM_VALUES)
+    minPos, maxPos = findMinMaxPos(hist)
+
+    # Precompute integral of histogram from left to right.
+    sum = 0
+    integral = []
+    for i in range(0, hist.shape[0]):
+        sum += hist[i]
+        integral.append(sum)
+
+    for x in range(0, img.shape[0]):
+        for y in range(0, img.shape[1]):
+            # Compute histogram value of pixel.
+            bin = int(img[x][y][0] / 255.0 * (MAX_LUM_VALUES - 1))
+            # Equalize pixel.
+            result[x][y] = (255.0 - 1.0) / (img.shape[0] * img.shape[1]) * integral[bin]
+
     return result
 
 
@@ -21,6 +51,18 @@ def equalizeHistogram(img):
 # function to apply a look-up table onto an image
 def applyLUT(img, LUT):
     result = img.copy()
+
+    grayscale = getLuminance(img)
+
+    for x in range(0, img.shape[0]):
+        for y in range(0, img.shape[1]):
+            # Compute histogram value of pixel.
+            bin = int(grayscale[x][y][0] / 255.0 * (MAX_LUM_VALUES - 1))
+
+            result[x][y][0] = LUT[bin]
+            result[x][y][1] = LUT[bin]
+            result[x][y][2] = LUT[bin]
+
     return result
 
 
@@ -29,6 +71,17 @@ def applyLUT(img, LUT):
 def findMinMaxPos(histogram):
     minPos = 0
     maxPos = 255
+
+    for x in range(0, histogram.shape[0]):
+        if histogram[x] > 0:
+            minPos = x
+            break
+
+    for x in range(histogram.shape[0] - 1, 0):
+        if histogram[x] > 0:
+            maxPos = x
+            break
+
     return minPos, maxPos
 
 
@@ -37,24 +90,117 @@ def findMinMaxPos(histogram):
 def calculateHistogram(img, nrBins):
     # create histogram vector
     histogram = np.zeros([nrBins], dtype=int)
+
+    for x in range(0, img.shape[0]):
+        for y in range(0, img.shape[1]):
+            bin = int(img[x][y][0] / 255.0 * (nrBins - 1))
+            histogram[bin] = histogram[bin] + 1
+
     return histogram
 
 
-def apply_log(img):
+def luminanceD65(rgb: np.ndarray) -> np.float64:
+    """
+    Compute the luminance value of the specified linear RGB values
+    according to the D65 white point.
+
+    @param rgb(np.ndarray): sRGB image
+
+    @returns The luminance value
+    """
+    return np.float64(rgb @ [0.2126, 0.7152, 0.0722])
+
+
+def getLuminance(img):
     result = img.copy()
+
+    for x in range(0, img.shape[0]):
+        for y in range(0, img.shape[1]):
+            lum = luminanceD65(img[x][y])
+            result[x][y][0] = lum
+            result[x][y][1] = lum
+            result[x][y][2] = lum
+
+    return result
+
+
+def apply_log(img):
+    grayscale = getLuminance(img)
+    result = img.copy()
+
+    # Logarithmic scale factor.
+    LOG_SCALE_FACTOR = 2.0
+
+    for x in range(0, img.shape[0]):
+        for y in range(0, img.shape[1]):
+
+            # Compute logarithmically scaled D65 luminace
+            # and clamp result to be smaller 255.
+            lum = min(255,
+                math.log(grayscale[x][y][0]/255.0 + 1)
+                * 255.0 * LOG_SCALE_FACTOR)
+
+            result[x][y][0] = lum
+            result[x][y][1] = lum
+            result[x][y][2] = lum
+
     return result
 
 
 def apply_exp(img):
+    grayscale = getLuminance(img)
     result = img.copy()
+
+    # Logarithmic scale factor.
+    EXP_SCALE_FACTOR = 0.5
+
+    for x in range(0, img.shape[0]):
+        for y in range(0, img.shape[1]):
+
+            # Compute logarithmically scaled D65 luminace
+            # and clamp result to be smaller 255.
+            lum = min(255,
+                (math.exp(grayscale[x][y][0]/255.0) - 1)
+                * 255.0 * EXP_SCALE_FACTOR)
+
+            result[x][y][0] = lum
+            result[x][y][1] = lum
+            result[x][y][2] = lum
+
     return result
 
 
 def apply_inverse(img):
+    grayscale = getLuminance(img)
     result = img.copy()
+
+    for x in range(0, img.shape[0]):
+        for y in range(0, img.shape[1]):
+
+            # Compute logarithmically scaled D65 luminace
+            # and clamp result to be smaller 255.
+            lum = 255.0 - grayscale[x][y][0]
+
+            result[x][y][0] = lum
+            result[x][y][1] = lum
+            result[x][y][2] = lum
+
     return result
 
 
 def apply_threshold(img, threshold):
+    grayscale = getLuminance(img)
     result = img.copy()
+
+    for x in range(0, img.shape[0]):
+        for y in range(0, img.shape[1]):
+
+            lum = 0
+            if grayscale[x][y][0] >= threshold:
+                lum = 255
+
+            result[x][y][0] = lum
+            result[x][y][1] = lum
+            result[x][y][2] = lum
+
     return result