imgcat, a cat in an image^W^W^Wfor images

gistfile1.txt

$ wget -q http://www.secretareaofvipquality.net/maiddog.png
$ ./imgcat maiddog.png 
                                          ▟████▙██▄█▟▄██▜▙                      
                                          ▞▜▙███▄▄▄▄▟██▜▞▚▄                     
                                         ▄████████████████▛▘                    
                                   ▝▀▀▘ ▖▖███▛▘▄▙▄▞▜██████▀▌                    
                                   ▐██▌ ▖▜██▛██████▌ ▀▜██▙▝█▚                   
                                   ▗▄▄▖ ▙▟█▌▟▀███▀▀▜█▛▄▟█████▙                  
                                       ▗▜██▙█▟████████████████▙                 
                                      ▗▄███▛▀▜█████████████████▌                
                                    ▗▄█████▖  ██████████████████                
                 ▖▗ ▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▜▚▟▀██▄   ▀▀▀▙████████████▌               
               ▖ ▗▄▖ ▀█████████████████▘   ▀▀▀▘   ▝▀▀▜█▟████████▖               
    ▗▄▄▖     ▝ ▗        ▝▀████████████▘            ▝████████████▘               
    ▗▄▄▄▄▟▙▟ ▞▘            ▀█████████▛          ▜▙████████████▜▌▘               
  ▗▄███▛██▙▙▖                ▝▀██████▌            ▝▀▀▀▜████▛▀█  ▄▄▄▖            
 ▟████████████▄                 ▝▀▜██▙            ▚▖        ▄▛  ▄▀██▄▄          
███▟█████████████▄▖                ▝▀█▖           ▐██▙▄▄▄▄▄▛▘  ▟██▙▄███▄▖       
███████████████████▙▖                █▌           ▐███████▛    ▝▀████▙▟█▙▄▄     
▙▟██████████▛▜███████▙▖              ▝▘      ▄▄▖  ▟██▛███▀        ▘▜████▄██▙▄▄▖ 
▜▛█████████▚▗██████████                  ▗▟███████▛   ▜▘▗▄▖      ▗▖ ▝▜█████▟▛▙▟ 
▌▗▖▝▀▘▀▀▛▀▗▐████████████▖              ▝ ▜█████████▄█▀▀▛▘ ▘       ▀  ▗ ▜█████▙▟ 
      ▄▄▄▄██████▀ ██████▄▖         ▗  ▄▄ ▄ ▀▀███████▄█▌            ▗▖▞▀         
       ▄▄██████▙▞▘▝▀  ▀▜█▛▚          ▄▄▄▟▄▟▀▗ ▄▜███████▘           ▝▀▘      ▀▀▀ 
      ▀▀▝  ▀███   ▘▖    ▝▀▀          ▀▀▀▀▀██▙ ▐▟███████▌           ▝▀▀▘         
      ▀▀▌ ▖ ▀▛▚ ▐█▛  ▗▄▗▄▖           ▀▀▀▀▀██▙ ▝▘▘▝▀▀▜▀▟▘                        
            ▗▄ ▀▟██▌▝    ▝                    ▝ ▀▚▄▄▄▗                          

imgcat.c

#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <wand/magick_wand.h>

void usage(char *argv_0) {
    fprintf(
        stderr,
        "Usage: %s [OPTIONS] FILENAME\n"
        "\n"
        "Options:\n"
        "\t-w N|auto\n"
        "\t\tSpecify width of the output, or `auto' for terminal width.\n"
        "\t\tPreserves aspect ratio if unspecified. Defaults to 80 if both\n"
        "\t\t-w and -h are omitted.\n"
        "\n"
        "\t-h N|auto\n"
        "\t\tSpecify height of the output, or `auto' for terminal height.\n"
        "\t\tPreserves aspect ratio if unspecified.\n"
        "\n"
        "\t-n\n"
        "\t\tNormalise image.\n"
        "\n"
        "\t-i\n"
        "\t\tInvert colours.\n"
        "\n",
        argv_0);
    exit(1);
}

int main(int argc, char **argv)
{
    int width = 0, height = 0, normalise = 0, invert = 0;
    char *shades[] = {" ", "▘", "▝", "▀", "▖", "▌", "▞", "▛",
                      "▗", "▚", "▐", "▜", "▄", "▙", "▟", "█"};


    /* Parse options. */

    int c;
    extern int optind;
    extern char *optarg;

    while ((c = getopt(argc, argv, "+w:h:ni")) != -1) {
        switch (c) {
        case 'w':
            if (strcmp(optarg, "auto") == 0) {
                struct winsize w;
                ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);
                width = w.ws_col;
            } else
                width = atoi(optarg);
            if (width < 0)
                usage(argv[0]);
            break;

        case 'h':
            if (strcmp(optarg, "auto") == 0) {
                struct winsize w;
                ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);
                height = w.ws_row;
            } else
                height = atoi(optarg);
            if (height < 0)
                usage(argv[0]);
            break;

        case 'n':
            normalise = 1;
            break;

        case 'i':
            invert = 1;
            break;
        
        default:
            usage(argv[0]);
        }
    }

    if (optind == argc)
        usage(argv[0]);


    /* Try to load image. */

    MagickWand *m_wand;

    MagickWandGenesis();
    m_wand = NewMagickWand();

    if (MagickReadImage(m_wand, argv[optind]) == MagickFalse) {
        perror("Can't into file");
        return 1;
    }


    /* Resize and optionally normalise and invert image. */

    size_t w = MagickGetImageWidth(m_wand),
           h = MagickGetImageHeight(m_wand);

    width *= 2;
    height *= 2;

    if (!height) {
        if (!width)
            width = 160;
        height = h * width / w / 2;
    }
    if (!width)
        width = w * height * 2 / h;

    if (width & 1) ++width;
    if (height & 1) ++height;

    MagickResizeImage(m_wand, width, height, LanczosFilter, 1.0);

    if (normalise) {
        MagickSetImageType(m_wand, GrayscaleType);
        MagickNormalizeImage(m_wand);
    }

    if (invert)
        MagickNegateImage(m_wand, MagickFalse);


    /* Output. */

    for (int i = 0; i < height; i += 2) {
        for (int j = 0; j < width; j += 2) {
            PixelWand *p_wand = NewPixelWand();
            double h, s, l;
            int p = 0;

            MagickGetImagePixelColor(m_wand, j, i, p_wand);
            PixelGetHSL(p_wand, &h, &s, &l);
            if (l > 0.5)
                p |= 1;

            MagickGetImagePixelColor(m_wand, j + 1, i, p_wand);
            PixelGetHSL(p_wand, &h, &s, &l);
            if (l > 0.5)
                p |= 2;

            MagickGetImagePixelColor(m_wand, j, i + 1, p_wand);
            PixelGetHSL(p_wand, &h, &s, &l);
            if (l > 0.5)
                p |= 4;

            MagickGetImagePixelColor(m_wand, j + 1, i + 1, p_wand);
            PixelGetHSL(p_wand, &h, &s, &l);
            if (l > 0.5)
                p |= 8;

            printf("%s", shades[p]);

            DestroyPixelWand(p_wand);
        }
        puts("");
    }

    return 0;
}

Makefile

MW = `MagickWand-config --cflags --ldflags --libs`
WARNS = -Wall -Wextra -pedantic -std=c99

.PHONY: all
all: imgcat

imgcat: imgcat.c
	$(CC) -o $@ $(MW) $(WARNS) $(CFLAGS) $^

.PHONY: clean
clean:
	rm -rf imgcat