diff --git a/Makefile b/Makefile
index c8271bc..f6a5168 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ LDIR = /opt/local/lib/
 LIBS = -lc -lpng16
 CFLAGS = -Wall -march=native -Ofast -Wa,-q
 OUT_DIR = build
-LABS = lab1_1 lab1_2 lab1_3 lab1_4 lab1_5 lab1_6 lab1_7 lab1_8 lab2_1 lab2_2 lab3 lab4_1 lab4_2 lab5 lab6 lab7
+LABS = lab1_1 lab1_2 lab1_3 lab1_4 lab1_5 lab1_6 lab1_7 lab1_8 lab2_1 lab2_2 lab3 lab4_1 lab4_2 lab4_3 lab5 lab6 lab7
 BINS = $(addprefix $(OUT_DIR)/,${LABS})
 OBJS = $(addsuffix .o,${BINS})
 
diff --git a/README.md b/README.md
index da83641..b98f819 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,7 @@ Here are the programs that I wrote during the Digital Image Processing class in
 4. Intensity transformations
     1. [Gamma correction](#gamma-correction-lab4_1c)
     2. [Linear contrast stretching](#linear-contrast-stretching-lab4_2c)
+    3. [Histogram equalization](#histogram-equalization-lab4_3c)
 5. [Convolution](#convolution-lab5c)
 6. [Median filter](#median-filter-lab6c)
 7. [Segmentation](#segmentation-lab7c)
@@ -111,6 +112,13 @@ Here are the programs that I wrote during the Digital Image Processing class in
 | ![Input](images/Auto.png) | ![Output](lab4_2/Auto_out_1000.png) |
 | ![Input](lab4_2/Auto_in_hist.png) | ![Output](lab4_2/Auto_out_1000_hist.png) |
 
+---
+## Histogram equalization ([lab4_3.c](lab4_3/lab4_3.c))
+| Input | Output |
+| ----- | ------ |
+| ![Input](images/Goldhill.png) | ![Output](lab4_3/Goldhill_out.png) |
+| ![Input](lab4_3/Goldhill_in_hist.png) | ![Output](lab4_3/Goldhill_out_hist.png) |
+
 ---
 ## Convolution ([lab5.c](lab5/lab5.c))
 | Input | Output ([11x11 blur](kernels/Blur_11.txt) kernel) |
diff --git a/lab4_3/Goldhill_in_hist.png b/lab4_3/Goldhill_in_hist.png
new file mode 100644
index 0000000..f5e0686
Binary files /dev/null and b/lab4_3/Goldhill_in_hist.png differ
diff --git a/lab4_3/Goldhill_out.png b/lab4_3/Goldhill_out.png
new file mode 100644
index 0000000..b3554ef
Binary files /dev/null and b/lab4_3/Goldhill_out.png differ
diff --git a/lab4_3/Goldhill_out_hist.png b/lab4_3/Goldhill_out_hist.png
new file mode 100644
index 0000000..8400dc9
Binary files /dev/null and b/lab4_3/Goldhill_out_hist.png differ
diff --git a/lab4_3/lab4_3.c b/lab4_3/lab4_3.c
new file mode 100644
index 0000000..cbc6cfd
--- /dev/null
+++ b/lab4_3/lab4_3.c
@@ -0,0 +1,60 @@
+#include <stdlib.h>
+#include "png_wrapper.h"
+#include "histogram.h"
+
+static void process_image(struct Image img)
+{
+	unsigned hist[MAX_COLOR + 1] = { };
+	for (size_t y = 0; y < img.height; y++)
+		for (size_t x = 0; x < img.width; x++)
+			hist[img.pixels[y][x]]++;
+
+	double cdf[MAX_COLOR + 1]; // Cumulative distributive function
+	unsigned total_pixels = img.height * img.width;
+	cdf[0] = hist[0] / (double) total_pixels;
+
+	for (size_t i = 1; i <= MAX_COLOR; i++)
+		cdf[i] = cdf[i - 1] + hist[i] / (double) total_pixels;
+
+	unsigned char lut[MAX_COLOR + 1];
+	for (size_t i = 0; i <= MAX_COLOR; i++)
+	{
+		int new = cdf[i] * MAX_COLOR;
+		lut[i] = new <= 255 ? new : 255;
+	}
+
+	for (size_t y = 0; y < img.height; y++)
+		for (size_t x = 0; x < img.width; x++)
+			img.pixels[y][x] = lut[img.pixels[y][x]];
+}
+
+int main(int argc, char * const argv[])
+{
+	if (argc != 5)
+		error("usage: %s <in_file> <out_file> <hist1_out_file> "
+			  "<hist2_out_file>", argv[0]);
+
+	char *input_filename  = argv[1];
+	char *output_filename = argv[2];
+	char *hist1_filename  = argv[3];
+	char *hist2_filename  = argv[4];
+
+	struct Image img = read_grayscale_png(input_filename);
+	printf("Input file \"%s\" opened (width = %u, height = %u)\n",
+		   input_filename, img.width, img.height);
+
+	struct Image hist = { HIST_WIDTH, HIST_HEIGHT };
+	alloc_pixels(&hist);
+	histogram(img, hist);
+	write_grayscale_png(hist, hist1_filename);
+
+	process_image(img);
+	write_grayscale_png(img, output_filename);
+
+	histogram(img, hist);
+	free_pixels(img);
+	write_grayscale_png(hist, hist2_filename);
+	free_pixels(hist);
+
+	return 0;
+}