Add gamma correction

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 lab2_1 lab2_2 lab3 lab4_2 lab5 lab6 lab7
+LABS = lab1_1 lab1_2 lab1_3 lab1_4 lab1_5 lab1_6 lab1_7 lab2_1 lab2_2 lab3 lab4_1 lab4_2 lab5 lab6 lab7
 BINS = $(addprefix $(OUT_DIR)/,${LABS})
 OBJS = $(addsuffix .o,${BINS})
 

README.md

@@ -15,6 +15,7 @@ Here are the programs that I wrote during the Digital Image Processing class in
     2. [Bilinear interpolation](#bilinear-interpolation-lab2_2c)
 3. [Alpha compositing](#alpha-compositing-lab3c)
 4. Intensity transformations
+    1. [Gamma correction](#gamma-correction-lab4_1c)
     2. [Linear contrast stretching](#linear-contrast-stretching-lab4_2c)
 5. [Convolution](#convolution-lab5c)
 6. [Median filter](#median-filter-lab6c)
@@ -80,6 +81,18 @@ Here are the programs that I wrote during the Digital Image Processing class in
 | ----- | ------ |
 | <ul><li>[Goldhill.png](images/Goldhill.png) as top</li><li>[Lena.png](images/Lena.png) as bottom</li><li>[Peppers.png](images/Peppers.png) as alpha channel</li></ul> | ![Output](lab3/Goldhill_Lena_Peppers_out.png) |
 
+---
+## Gamma correction ([lab4_1.c](lab4_1/lab4_1.c))
+| Input | Output (c = 1.0, gamma = 0.6) |
+| ----- | ------ |
+| ![Input](images/House.png) | ![Output](lab4_1/House_out_1.0_0.6.png) |
+| ![Input](lab4_1/House_in_hist.png) | ![Output](lab4_1/House_out_1.0_0.6_hist.png) |
+
+| Input | Output (c = 1.5, gamma = 1.5) |
+| ----- | ------ |
+| ![Input](images/House.png) | ![Output](lab4_1/House_out_1.5_1.5.png) |
+| ![Input](lab4_1/House_in_hist.png) | ![Output](lab4_1/House_out_1.5_1.5_hist.png) |
+
 ---
 ## Linear contrast stretching ([lab4_2.c](lab4_2/lab4_2.c))
 | Input | Output (delta = 1000) |

lab4_1/lab4_1.c

@@ -0,0 +1,62 @@
+#include <string.h>
+#include <stdlib.h>
+#include <math.h>
+#include "png_wrapper.h"
+#include "histogram.h"
+
+static void process_image(struct Image img, double c, double gamma)
+{
+	for (int y = 0; y < img.height; y++)
+		for (int x = 0; x < img.width; x++)
+		{
+			double in = img.pixels[y][x] / 255.0;
+			int out = c * pow(in, gamma) * 255.0 + 0.5;
+			if (out > 255) out = 255;
+			img.pixels[y][x] = out;
+		}
+}
+
+int main(int argc, char * const argv[])
+{
+	if (argc != 7)
+		error("usage: %s <in_file> <out_file> <hist1_out_file> "
+			  "<hist2_out_file> <c (0.0-50.0)> <gamma (0.0-50.0)>", argv[0]);
+
+	char *input_filename  = argv[1];
+	char *output_filename = argv[2];
+	char *hist1_filename  = argv[3];
+	char *hist2_filename  = argv[4];
+	char *s_c             = argv[5];
+	char *s_gamma         = argv[6];
+
+	double c = atof(s_c);
+	if (c < 0.0 || c > 50.0)
+		error("wrong c (%f)", c);
+
+	double gamma = atof(s_gamma);
+	if (gamma < 0.0 || gamma > 50.0)
+		error("wrong gamma (%f)", gamma);
+
+	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 hist1 = { HIST_WIDTH, HIST_HEIGHT };
+	alloc_pixels(&hist1);
+	histogram(img, hist1);
+	write_grayscale_png(hist1, hist1_filename);
+	free_pixels(hist1);
+
+	process_image(img, c, gamma);
+
+	struct Image hist2 = { HIST_WIDTH, HIST_HEIGHT };
+	alloc_pixels(&hist2);
+	histogram(img, hist2);
+	write_grayscale_png(hist2, hist2_filename);
+	free_pixels(hist2);
+
+	write_grayscale_png(img, output_filename);
+	free_pixels(img);
+
+	return 0;
+}