Initial commit

1 files changed, 153 insertions, 0 deletions

diff --git a/pixel-count.c b/pixel-count.c
new file mode 100644
index 0000000..50cdeac
--- /dev/null
+++ b/pixel-count.c
@@ -0,0 +1,153 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <math.h>
+#include "zlib.h"
+
+#define HSIZE 8
+#define CSIZE 4
+
+
+int byteArrayEquals(uint8_t *b1, uint8_t *b2, uint32_t size){
+	uint32_t i = 0;
+	while(i < size && b1[i] == b2[i])
+		++i;
+	return i == size;
+}
+
+uint8_t paethPredictor(uint8_t a, uint8_t b, uint8_t c){
+	uint8_t p = (a + b - c)%256;	// initial estimate
+	uint8_t pa = abs(p - a);		// distances to a, b, c
+	uint8_t pb = abs(p - b);
+	uint8_t pc = abs(p - c);
+	// return nearest of a,b,c,
+	// breaking ties in order a,b,c.
+	if(pa <= pb && pa <= pc)
+		return a;
+	else if(pb <= pc)
+		return b;
+	else
+		return c;
+}
+
+bool matchRGB(uint8_t c1[3], uint8_t c2[3]){
+	return (c1[0] == c2[0]) && (c1[1] == c2[1]) && (c1[2] == c2[2]);
+}
+
+
+uint8_t PNG[HSIZE] = {0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A};
+uint8_t IHDR[CSIZE] = {0x49, 0x48, 0x44, 0x52};
+uint8_t IDAT[CSIZE] = {0x49, 0x44, 0x41, 0x54};
+uint8_t	IEND[CSIZE] = {0x49, 0x45, 0x4E, 0x44};
+
+
+int main(){
+
+	uint32_t pixels = 0;
+
+	FILE *fp = fopen("download.png", "rb");	// File to read
+	uint8_t red[3] = {0xFF, 0x00, 0x00};	// Color to look for
+
+	// Read PNG header
+	uint8_t header[HSIZE];
+	fread(header, sizeof(uint8_t), HSIZE, fp);
+	if(!byteArrayEquals(header, PNG, HSIZE)){
+		fprintf(stderr, "Invalid PNG signature\n");
+		fclose(fp);
+		return 0;
+	}
+	
+	uint32_t width = 0, height = 0;
+	uint8_t bitDepth, colorType, compressionMethod, filterMethod, interlaceMethod;
+
+	// Start reading file
+	while(!feof(fp)){
+
+		uint8_t lenbuf[CSIZE], ctype[CSIZE], crcbuf[CSIZE];
+
+		// Read length of chunk
+		fread(lenbuf, sizeof(uint8_t), CSIZE, fp);
+		uint32_t len = 0;
+		for(int i = 0; i < CSIZE; ++i){
+			len += lenbuf[i]<<(8*(3-i));
+		}
+		uint8_t *data = calloc(len, sizeof(uint8_t));
+
+		// Read chunk type
+		fread(ctype, sizeof(uint8_t), CSIZE, fp);
+
+		// Read data according to type
+		fread(data, sizeof(uint8_t), len, fp);
+		if(byteArrayEquals(ctype, IHDR, CSIZE)){
+			for(int i = 0; i < 4; ++i){
+				width += data[i]<<(8*(3-i));
+				height += data[i+4]<<(8*(3-i));
+			}
+			bitDepth = data[8];
+			colorType = data[9];
+			compressionMethod = data[10];
+			filterMethod = data[11];
+			interlaceMethod = data[12];
+		}else if(byteArrayEquals(ctype, IDAT, CSIZE)){
+
+			// Only implementing RGB
+			if(colorType == 2){
+
+				uint8_t *d = malloc(height*(1 + width*3)*sizeof(uint8_t));
+				uLongf nlen;
+				uncompress((Bytef *)d, &nlen, (Bytef *)data, len);
+
+				for(uint16_t i = 0; i < height; ++i){
+
+					uint8_t color[3] = {0x00, 0x00, 0x00};
+					uint8_t filterType = d[i*(1+width*3) + 0];
+					uint8_t bpp = 3*(bitDepth/8);
+
+					for(uint16_t j = 1; j < 1+width*3; ++j){
+						
+						uint8_t ant = (j-bpp < 1) ? 0 : d[i*(1+width*3) + j-bpp];
+						uint8_t prev = (i == 0) ? 0 : d[(i-1)*(1+width*3) + j];
+						uint8_t antprev = (j-bpp < 1 || i == 0) ? 0 : d[(i-1)*(1+width*3) + j-bpp];
+
+						switch(filterType){
+							case 1:
+								d[i*(1+width*3) + j] = (d[i*(1+width*3) + j] + ant)%256;
+								break;
+							case 2:
+								d[i*(1+width*3) + j] = (d[i*(1+width*3) + j] + prev)%256;
+								break;
+							case 3:
+								d[i*(1+width*3) + j] = (d[i*(1+width*3) + j] + (uint8_t)floor((ant + prev)/2))%256;
+								break;
+							case 4:
+								d[i*(1+width*3) + j] = (d[i*(1+width*3) + j] + paethPredictor(ant, prev, antprev))%256;
+								break;
+						}
+						
+						// Stores pixels in pixels array
+						color[(j-1)%3] = d[i*(1+width*3) + j];
+
+						// Counts red pixels
+						if(j%3 == 0 && matchRGB(color, red)){
+							++pixels;
+						}
+					}
+				}	
+			}
+		}
+
+		// Read CRC checksum
+		fread(crcbuf, sizeof(uint8_t), CSIZE, fp);
+
+		if(byteArrayEquals(ctype, IEND, CSIZE)){
+			break;	
+		}
+	}
+	
+	fclose(fp);
+
+	printf("Pixels: %d\n", pixels);
+
+	return 0;
+}
\ No newline at end of file