Copy glitch from pngo

3 files changed, 733 insertions, 1 deletions

diff --git a/bin/.gitignore b/bin/.gitignore
index 77c1277c..1904feb4 100644
--- a/bin/.gitignore
+++ b/bin/.gitignore
@@ -3,6 +3,7 @@ tags
 atch
 dtch
 gfxx
+glitch
 hnel
 pbcopy
 pbd
diff --git a/bin/Makefile b/bin/Makefile
index bb834767..af587376 100644
--- a/bin/Makefile
+++ b/bin/Makefile
@@ -1,4 +1,4 @@
-ANY_BINS = atch dtch gfxx hnel pbcopy pbd pbpaste pngo wake xx
+ANY_BINS = atch dtch gfxx glitch hnel pbcopy pbd pbpaste pngo wake xx
 BSD_BINS = klon watch
 LIN_BINS = bri fbatt fbclock
 ALL_BINS = $(ANY_BINS) $(BSD_BINS) $(LIN_BINS)
diff --git a/bin/glitch.c b/bin/glitch.c
new file mode 100644
index 00000000..5ce62797
--- /dev/null
+++ b/bin/glitch.c
@@ -0,0 +1,731 @@
+/* Copyright (c) 2018, Curtis McEnroe <programble@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <arpa/inet.h>
+#include <assert.h>
+#include <err.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sysexits.h>
+#include <unistd.h>
+#include <zlib.h>
+
+#define PACKED __attribute__((packed))
+#define PAIR(a, b) ((uint16_t)(a) << 8 | (uint16_t)(b))
+
+#define CRC_INIT (crc32(0, Z_NULL, 0))
+
+static bool verbose;
+static const char *path;
+static FILE *file;
+static uint32_t crc;
+
+static void readExpect(void *ptr, size_t size, const char *expect) {
+    fread(ptr, size, 1, file);
+    if (ferror(file)) err(EX_IOERR, "%s", path);
+    if (feof(file)) errx(EX_DATAERR, "%s: missing %s", path, expect);
+    crc = crc32(crc, ptr, size);
+}
+
+static void writeExpect(const void *ptr, size_t size) {
+    fwrite(ptr, size, 1, file);
+    if (ferror(file)) err(EX_IOERR, "%s", path);
+    crc = crc32(crc, ptr, size);
+}
+
+static const uint8_t SIGNATURE[8] = {
+    0x89, 'P', 'N', 'G', '\r', '\n', 0x1A, '\n'
+};
+
+static void readSignature(void) {
+    uint8_t signature[8];
+    readExpect(signature, 8, "signature");
+    if (0 != memcmp(signature, SIGNATURE, 8)) {
+        errx(EX_DATAERR, "%s: invalid signature", path);
+    }
+}
+
+static void writeSignature(void) {
+    writeExpect(SIGNATURE, sizeof(SIGNATURE));
+}
+
+struct PACKED Chunk {
+    uint32_t size;
+    char type[4];
+};
+
+static bool ancillary(struct Chunk chunk) {
+    return chunk.type[0] & 0x20;
+}
+
+static const char *typeStr(struct Chunk chunk) {
+    static char buf[5];
+    memcpy(buf, chunk.type, 4);
+    return buf;
+}
+
+static struct Chunk readChunk(void) {
+    struct Chunk chunk;
+    readExpect(&chunk, sizeof(chunk), "chunk");
+    chunk.size = ntohl(chunk.size);
+    crc = crc32(CRC_INIT, (Byte *)chunk.type, sizeof(chunk.type));
+    return chunk;
+}
+
+static void writeChunk(struct Chunk chunk) {
+    chunk.size = htonl(chunk.size);
+    writeExpect(&chunk, sizeof(chunk));
+    crc = crc32(CRC_INIT, (Byte *)chunk.type, sizeof(chunk.type));
+}
+
+static void readCrc(void) {
+    uint32_t expected = crc;
+    uint32_t found;
+    readExpect(&found, sizeof(found), "CRC32");
+    found = ntohl(found);
+    if (found != expected) {
+        errx(
+            EX_DATAERR, "%s: expected CRC32 %08X, found %08X",
+            path, expected, found
+        );
+    }
+}
+
+static void writeCrc(void) {
+    uint32_t net = htonl(crc);
+    writeExpect(&net, sizeof(net));
+}
+
+static void skipChunk(struct Chunk chunk) {
+    uint8_t discard[chunk.size];
+    readExpect(discard, sizeof(discard), "chunk data");
+    readCrc();
+}
+
+static struct PACKED {
+    uint32_t width;
+    uint32_t height;
+    uint8_t depth;
+    enum PACKED {
+        GRAYSCALE       = 0,
+        TRUECOLOR       = 2,
+        INDEXED         = 3,
+        GRAYSCALE_ALPHA = 4,
+        TRUECOLOR_ALPHA = 6,
+    } color;
+    enum PACKED { DEFLATE } compression;
+    enum PACKED { ADAPTIVE } filter;
+    enum PACKED { PROGRESSIVE, ADAM7 } interlace;
+} header;
+
+static size_t lineSize(void) {
+    switch (header.color) {
+        case GRAYSCALE:       return (header.width * 1 * header.depth + 7) / 8;
+        case TRUECOLOR:       return (header.width * 3 * header.depth + 7) / 8;
+        case INDEXED:         return (header.width * 1 * header.depth + 7) / 8;
+        case GRAYSCALE_ALPHA: return (header.width * 2 * header.depth + 7) / 8;
+        case TRUECOLOR_ALPHA: return (header.width * 4 * header.depth + 7) / 8;
+        default: abort();
+    }
+}
+
+static size_t dataSize(void) {
+    return (1 + lineSize()) * header.height;
+}
+
+static const char *COLOR_STR[] = {
+    [GRAYSCALE] = "grayscale",
+    [TRUECOLOR] = "truecolor",
+    [INDEXED] = "indexed",
+    [GRAYSCALE_ALPHA] = "grayscale alpha",
+    [TRUECOLOR_ALPHA] = "truecolor alpha",
+};
+static void printHeader(void) {
+    fprintf(
+        stderr,
+        "%s: %ux%u %hhu-bit %s\n",
+        path,
+        header.width, header.height,
+        header.depth, COLOR_STR[header.color]
+    );
+}
+
+static void readHeader(void) {
+    struct Chunk ihdr = readChunk();
+    if (0 != memcmp(ihdr.type, "IHDR", 4)) {
+        errx(EX_DATAERR, "%s: expected IHDR, found %s", path, typeStr(ihdr));
+    }
+    if (ihdr.size != sizeof(header)) {
+        errx(
+            EX_DATAERR, "%s: expected IHDR size %zu, found %u",
+            path, sizeof(header), ihdr.size
+        );
+    }
+    readExpect(&header, sizeof(header), "header");
+    readCrc();
+
+    header.width = ntohl(header.width);
+    header.height = ntohl(header.height);
+
+    if (!header.width) errx(EX_DATAERR, "%s: invalid width 0", path);
+    if (!header.height) errx(EX_DATAERR, "%s: invalid height 0", path);
+    switch (PAIR(header.color, header.depth)) {
+        case PAIR(GRAYSCALE, 1):
+        case PAIR(GRAYSCALE, 2):
+        case PAIR(GRAYSCALE, 4):
+        case PAIR(GRAYSCALE, 8):
+        case PAIR(GRAYSCALE, 16):
+        case PAIR(TRUECOLOR, 8):
+        case PAIR(TRUECOLOR, 16):
+        case PAIR(INDEXED, 1):
+        case PAIR(INDEXED, 2):
+        case PAIR(INDEXED, 4):
+        case PAIR(INDEXED, 8):
+        case PAIR(GRAYSCALE_ALPHA, 8):
+        case PAIR(GRAYSCALE_ALPHA, 16):
+        case PAIR(TRUECOLOR_ALPHA, 8):
+        case PAIR(TRUECOLOR_ALPHA, 16):
+            break;
+        default:
+            errx(
+                EX_DATAERR, "%s: invalid color type %hhu and bit depth %hhu",
+                path, header.color, header.depth
+            );
+    }
+    if (header.compression != DEFLATE) {
+        errx(
+            EX_DATAERR, "%s: invalid compression method %hhu",
+            path, header.compression
+        );
+    }
+    if (header.filter != ADAPTIVE) {
+        errx(EX_DATAERR, "%s: invalid filter method %hhu", path, header.filter);
+    }
+    if (header.interlace > ADAM7) {
+        errx(EX_DATAERR, "%s: invalid interlace method %hhu", path, header.interlace);
+    }
+
+    if (verbose) printHeader();
+}
+
+static void writeHeader(void) {
+    if (verbose) printHeader();
+
+    struct Chunk ihdr = { .size = sizeof(header), .type = "IHDR" };
+    writeChunk(ihdr);
+    header.width = htonl(header.width);
+    header.height = htonl(header.height);
+    writeExpect(&header, sizeof(header));
+    writeCrc();
+
+    header.width = ntohl(header.width);
+    header.height = ntohl(header.height);
+}
+
+static struct {
+    uint32_t len;
+    uint8_t entries[256][3];
+} palette;
+
+static uint16_t paletteIndex(const uint8_t *rgb) {
+    uint16_t i;
+    for (i = 0; i < palette.len; ++i) {
+        if (0 == memcmp(palette.entries[i], rgb, 3)) break;
+    }
+    return i;
+}
+
+static bool paletteAdd(const uint8_t *rgb) {
+    uint16_t i = paletteIndex(rgb);
+    if (i < palette.len) return true;
+    if (i == 256) return false;
+    memcpy(palette.entries[palette.len++], rgb, 3);
+    return true;
+}
+
+static void readPalette(void) {
+    struct Chunk chunk;
+    for (;;) {
+        chunk = readChunk();
+        if (0 == memcmp(chunk.type, "PLTE", 4)) {
+            break;
+        } else if (ancillary(chunk)) {
+            skipChunk(chunk);
+        } else {
+            errx(
+                EX_DATAERR, "%s: expected PLTE chunk, found %s",
+                path, typeStr(chunk)
+            );
+        }
+    }
+    if (chunk.size % 3) {
+        errx(EX_DATAERR, "%s: PLTE size %u not divisible by 3", path, chunk.size);
+    }
+
+    palette.len = chunk.size / 3;
+    readExpect(palette.entries, chunk.size, "palette data");
+    readCrc();
+
+    if (verbose) fprintf(stderr, "%s: palette length %u\n", path, palette.len);
+}
+
+static void writePalette(void) {
+    if (verbose) fprintf(stderr, "%s: palette length %u\n", path, palette.len);
+    struct Chunk plte = { .size = 3 * palette.len, .type = "PLTE" };
+    writeChunk(plte);
+    writeExpect(palette.entries, plte.size);
+    writeCrc();
+}
+
+static uint8_t *data;
+
+static void allocData(void) {
+    data = malloc(dataSize());
+    if (!data) err(EX_OSERR, "malloc(%zu)", dataSize());
+}
+
+static void readData(void) {
+    if (verbose) fprintf(stderr, "%s: data size %zu\n", path, dataSize());
+
+    struct z_stream_s stream = { .next_out = data, .avail_out = dataSize() };
+    int error = inflateInit(&stream);
+    if (error != Z_OK) errx(EX_SOFTWARE, "%s: inflateInit: %s", path, stream.msg);
+
+    for (;;) {
+        struct Chunk chunk = readChunk();
+        if (0 == memcmp(chunk.type, "IDAT", 4)) {
+            uint8_t idat[chunk.size];
+            readExpect(idat, sizeof(idat), "image data");
+            readCrc();
+
+            stream.next_in = idat;
+            stream.avail_in = sizeof(idat);
+            int error = inflate(&stream, Z_SYNC_FLUSH);
+            if (error == Z_STREAM_END) break;
+            if (error != Z_OK) errx(EX_DATAERR, "%s: inflate: %s", path, stream.msg);
+
+        } else if (0 == memcmp(chunk.type, "IEND", 4)) {
+            errx(EX_DATAERR, "%s: missing IDAT chunk", path);
+        } else if (ancillary(chunk)) {
+            skipChunk(chunk);
+        } else {
+            errx(
+                EX_CONFIG, "%s: unsupported critical chunk %s",
+                path, typeStr(chunk)
+            );
+        }
+    }
+
+    inflateEnd(&stream);
+    if (stream.total_out != dataSize()) {
+        errx(
+            EX_DATAERR, "%s: expected data size %zu, found %lu",
+            path, dataSize(), stream.total_out
+        );
+    }
+
+    if (verbose) fprintf(stderr, "%s: deflate size %lu\n", path, stream.total_in);
+}
+
+static void writeData(void) {
+    if (verbose) fprintf(stderr, "%s: data size %zu\n", path, dataSize());
+
+    uLong size = compressBound(dataSize());
+    uint8_t deflate[size];
+    int error = compress2(deflate, &size, data, dataSize(), Z_BEST_COMPRESSION);
+    if (error != Z_OK) errx(EX_SOFTWARE, "%s: compress2: %d", path, error);
+
+    struct Chunk idat = { .size = size, .type = "IDAT" };
+    writeChunk(idat);
+    writeExpect(deflate, size);
+    writeCrc();
+
+    if (verbose) fprintf(stderr, "%s: deflate size %lu\n", path, size);
+}
+
+static void writeEnd(void) {
+    struct Chunk iend = { .size = 0, .type = "IEND" };
+    writeChunk(iend);
+    writeCrc();
+}
+
+enum PACKED Filter {
+    NONE,
+    SUB,
+    UP,
+    AVERAGE,
+    PAETH,
+};
+#define FILTER_COUNT (PAETH + 1)
+
+struct Bytes {
+    uint8_t x;
+    uint8_t a;
+    uint8_t b;
+    uint8_t c;
+};
+
+static uint8_t paethPredictor(struct Bytes f) {
+    int32_t p = (int32_t)f.a + (int32_t)f.b - (int32_t)f.c;
+    int32_t pa = abs(p - (int32_t)f.a);
+    int32_t pb = abs(p - (int32_t)f.b);
+    int32_t pc = abs(p - (int32_t)f.c);
+    if (pa <= pb && pa <= pc) return f.a;
+    if (pb <= pc) return f.b;
+    return f.c;
+}
+
+static uint8_t recon(enum Filter type, struct Bytes f) {
+    switch (type) {
+        case NONE:    return f.x;
+        case SUB:     return f.x + f.a;
+        case UP:      return f.x + f.b;
+        case AVERAGE: return f.x + ((uint32_t)f.a + (uint32_t)f.b) / 2;
+        case PAETH:   return f.x + paethPredictor(f);
+        default:      abort();
+    }
+}
+
+static uint8_t filt(enum Filter type, struct Bytes f) {
+    switch (type) {
+        case NONE:    return f.x;
+        case SUB:     return f.x - f.a;
+        case UP:      return f.x - f.b;
+        case AVERAGE: return f.x - ((uint32_t)f.a + (uint32_t)f.b) / 2;
+        case PAETH:   return f.x - paethPredictor(f);
+        default:      abort();
+    }
+}
+
+static struct Line {
+    enum Filter type;
+    uint8_t data[];
+} **lines;
+
+static void allocLines(void) {
+    lines = calloc(header.height, sizeof(*lines));
+    if (!lines) err(EX_OSERR, "calloc(%u, %zu)", header.height, sizeof(*lines));
+}
+
+static void scanlines(void) {
+    size_t stride = 1 + lineSize();
+    for (uint32_t y = 0; y < header.height; ++y) {
+        lines[y] = (struct Line *)&data[y * stride];
+        if (lines[y]->type >= FILTER_COUNT) {
+            errx(EX_DATAERR, "%s: invalid filter type %hhu", path, lines[y]->type);
+        }
+    }
+}
+
+static struct Bytes origBytes(uint32_t y, size_t i) {
+    size_t pixelSize = lineSize() / header.width;
+    if (!pixelSize) pixelSize = 1;
+    bool a = (i >= pixelSize), b = (y > 0), c = (a && b);
+    return (struct Bytes) {
+        .x = lines[y]->data[i],
+        .a = a ? lines[y]->data[i - pixelSize] : 0,
+        .b = b ? lines[y - 1]->data[i] : 0,
+        .c = c ? lines[y - 1]->data[i - pixelSize] : 0,
+    };
+}
+
+static void reconData(void) {
+    for (uint32_t y = 0; y < header.height; ++y) {
+        for (size_t i = 0; i < lineSize(); ++i) {
+            lines[y]->data[i] =
+                recon(lines[y]->type, origBytes(y, i));
+        }
+        lines[y]->type = NONE;
+    }
+}
+
+static void filterData(void) {
+    if (header.color == INDEXED || header.depth < 8) return;
+    for (uint32_t y = header.height - 1; y < header.height; --y) {
+        uint8_t filter[FILTER_COUNT][lineSize()];
+        uint32_t heuristic[FILTER_COUNT] = {0};
+        enum Filter minType = NONE;
+        for (enum Filter type = NONE; type < FILTER_COUNT; ++type) {
+            for (size_t i = 0; i < lineSize(); ++i) {
+                filter[type][i] = filt(type, origBytes(y, i));
+                heuristic[type] += abs((int8_t)filter[type][i]);
+            }
+            if (heuristic[type] < heuristic[minType]) minType = type;
+        }
+        lines[y]->type = minType;
+        memcpy(lines[y]->data, filter[minType], lineSize());
+    }
+}
+
+static void discardAlpha(void) {
+    if (header.color != GRAYSCALE_ALPHA && header.color != TRUECOLOR_ALPHA) return;
+    size_t sampleSize = header.depth / 8;
+    size_t pixelSize = sampleSize * (header.color == GRAYSCALE_ALPHA ? 2 : 4);
+    size_t colorSize = pixelSize - sampleSize;
+    for (uint32_t y = 0; y < header.height; ++y) {
+        for (uint32_t x = 0; x < header.width; ++x) {
+            for (size_t i = 0; i < sampleSize; ++i) {
+                if (lines[y]->data[x * pixelSize + colorSize + i] != 0xFF) return;
+            }
+        }
+    }
+
+    uint8_t *ptr = data;
+    for (uint32_t y = 0; y < header.height; ++y) {
+        *ptr++ = lines[y]->type;
+        for (uint32_t x = 0; x < header.width; ++x) {
+            memmove(ptr, &lines[y]->data[x * pixelSize], colorSize);
+            ptr += colorSize;
+        }
+    }
+    header.color = (header.color == GRAYSCALE_ALPHA) ? GRAYSCALE : TRUECOLOR;
+    scanlines();
+}
+
+static void discardColor(void) {
+    if (header.color != TRUECOLOR && header.color != TRUECOLOR_ALPHA) return;
+    size_t sampleSize = header.depth / 8;
+    size_t pixelSize = sampleSize * (header.color == TRUECOLOR ? 3 : 4);
+    for (uint32_t y = 0; y < header.height; ++y) {
+        for (uint32_t x = 0; x < header.width; ++x) {
+            uint8_t *r = &lines[y]->data[x * pixelSize];
+            uint8_t *g = r + sampleSize;
+            uint8_t *b = g + sampleSize;
+            if (0 != memcmp(r, g, sampleSize)) return;
+            if (0 != memcmp(g, b, sampleSize)) return;
+        }
+    }
+
+    uint8_t *ptr = data;
+    for (uint32_t y = 0; y < header.height; ++y) {
+        *ptr++ = lines[y]->type;
+        for (uint32_t x = 0; x < header.width; ++x) {
+            uint8_t *pixel = &lines[y]->data[x * pixelSize];
+            memmove(ptr, pixel, sampleSize);
+            ptr += sampleSize;
+            if (header.color == TRUECOLOR_ALPHA) {
+                memmove(ptr, pixel + 3 * sampleSize, sampleSize);
+                ptr += sampleSize;
+            }
+        }
+    }
+    header.color = (header.color == TRUECOLOR) ? GRAYSCALE : GRAYSCALE_ALPHA;
+    scanlines();
+}
+
+static void indexColor(void) {
+    if (header.color != TRUECOLOR || header.depth != 8) return;
+    for (uint32_t y = 0; y < header.height; ++y) {
+        for (uint32_t x = 0; x < header.width; ++x) {
+            if (!paletteAdd(&lines[y]->data[x * 3])) return;
+        }
+    }
+
+    uint8_t *ptr = data;
+    for (uint32_t y = 0; y < header.height; ++y) {
+        *ptr++ = lines[y]->type;
+        for (uint32_t x = 0; x < header.width; ++x) {
+            *ptr++ = paletteIndex(&lines[y]->data[x * 3]);
+        }
+    }
+    header.color = INDEXED;
+    scanlines();
+}
+
+static void reduceDepth8(void) {
+    if (header.color != GRAYSCALE && header.color != INDEXED) return;
+    if (header.depth != 8) return;
+    if (header.color == GRAYSCALE) {
+        for (uint32_t y = 0; y < header.height; ++y) {
+            for (size_t i = 0; i < lineSize(); ++i) {
+                uint8_t a = lines[y]->data[i];
+                if ((a >> 4) != (a & 0x0F)) return;
+            }
+        }
+    } else if (palette.len > 16) {
+        return;
+    }
+
+    uint8_t *ptr = data;
+    for (uint32_t y = 0; y < header.height; ++y) {
+        *ptr++ = lines[y]->type;
+        for (size_t i = 0; i < lineSize(); i += 2) {
+            uint8_t iByte = lines[y]->data[i];
+            uint8_t jByte = (i + 1 < lineSize()) ? lines[y]->data[i + 1] : 0;
+            uint8_t a = iByte & 0x0F;
+            uint8_t b = jByte & 0x0F;
+            *ptr++ = a << 4 | b;
+        }
+    }
+    header.depth = 4;
+    scanlines();
+}
+
+static void reduceDepth4(void) {
+    if (header.depth != 4) return;
+    if (header.color == GRAYSCALE) {
+        for (uint32_t y = 0; y < header.height; ++y) {
+            for (size_t i = 0; i < lineSize(); ++i) {
+                uint8_t a = lines[y]->data[i] >> 4;
+                uint8_t b = lines[y]->data[i] & 0x0F;
+                if ((a >> 2) != (a & 0x03)) return;
+                if ((b >> 2) != (b & 0x03)) return;
+            }
+        }
+    } else if (palette.len > 4) {
+        return;
+    }
+
+    uint8_t *ptr = data;
+    for (uint32_t y = 0; y < header.height; ++y) {
+        *ptr++ = lines[y]->type;
+        for (size_t i = 0; i < lineSize(); i += 2) {
+            uint8_t iByte = lines[y]->data[i];
+            uint8_t jByte = (i + 1 < lineSize()) ? lines[y]->data[i + 1] : 0;
+            uint8_t a = iByte >> 4 & 0x03, b = iByte & 0x03;
+            uint8_t c = jByte >> 4 & 0x03, d = jByte & 0x03;
+            *ptr++ = a << 6 | b << 4 | c << 2 | d;
+        }
+    }
+    header.depth = 2;
+    scanlines();
+}
+
+static void reduceDepth2(void) {
+    if (header.depth != 2) return;
+    if (header.color == GRAYSCALE) {
+        for (uint32_t y = 0; y < header.height; ++y) {
+            for (size_t i = 0; i < lineSize(); ++i) {
+                uint8_t a = lines[y]->data[i] >> 6;
+                uint8_t b = lines[y]->data[i] >> 4 & 0x03;
+                uint8_t c = lines[y]->data[i] >> 2 & 0x03;
+                uint8_t d = lines[y]->data[i] & 0x03;
+                if ((a >> 1) != (a & 0x01)) return;
+                if ((b >> 1) != (b & 0x01)) return;
+                if ((c >> 1) != (c & 0x01)) return;
+                if ((d >> 1) != (d & 0x01)) return;
+            }
+        }
+    } else if (palette.len > 2) {
+        return;
+    }
+
+    uint8_t *ptr = data;
+    for (uint32_t y = 0; y < header.height; ++y) {
+        *ptr++ = lines[y]->type;
+        for (size_t i = 0; i < lineSize(); i += 2) {
+            uint8_t iByte = lines[y]->data[i];
+            uint8_t jByte = (i + 1 < lineSize()) ? lines[y]->data[i + 1] : 0;
+            uint8_t a = iByte >> 6 & 0x01, b = iByte >> 4 & 0x01;
+            uint8_t c = iByte >> 2 & 0x01, d = iByte & 0x01;
+            uint8_t e = jByte >> 6 & 0x01, f = jByte >> 4 & 0x01;
+            uint8_t g = jByte >> 2 & 0x01, h = jByte & 0x01;
+            *ptr++ = a << 7 | b << 6 | c << 5 | d << 4 | e << 3 | f << 2 | g << 1 | h;
+        }
+    }
+    header.depth = 1;
+    scanlines();
+}
+
+static void reduceDepth(void) {
+    reduceDepth8();
+    reduceDepth4();
+    reduceDepth2();
+}
+
+static void optimize(const char *inPath, const char *outPath) {
+    if (inPath) {
+        path = inPath;
+        file = fopen(path, "r");
+        if (!file) err(EX_NOINPUT, "%s", path);
+    } else {
+        path = "(stdin)";
+        file = stdin;
+    }
+
+    readSignature();
+    readHeader();
+    if (header.interlace != PROGRESSIVE) {
+        errx(
+            EX_CONFIG, "%s: unsupported interlace method %hhu",
+            path, header.interlace
+        );
+    }
+    if (header.color == INDEXED) readPalette();
+    allocData();
+    readData();
+    fclose(file);
+
+    allocLines();
+    scanlines();
+    reconData();
+
+    discardAlpha();
+    discardColor();
+    indexColor();
+    reduceDepth();
+    filterData();
+    free(lines);
+
+    if (outPath) {
+        path = outPath;
+        file = fopen(path, "w");
+        if (!file) err(EX_CANTCREAT, "%s", path);
+    } else {
+        path = "(stdout)";
+        file = stdout;
+    }
+
+    writeSignature();
+    writeHeader();
+    if (header.color == INDEXED) writePalette();
+    writeData();
+    writeEnd();
+    free(data);
+
+    int error = fclose(file);
+    if (error) err(EX_IOERR, "%s", path);
+}
+
+int main(int argc, char *argv[]) {
+    bool stdio = false;
+    char *output = NULL;
+
+    int opt;
+    while (0 < (opt = getopt(argc, argv, "co:v"))) {
+        switch (opt) {
+            case 'c': stdio = true; break;
+            case 'o': output = optarg; break;
+            case 'v': verbose = true; break;
+            default: return EX_USAGE;
+        }
+    }
+
+    if (argc - optind == 1 && (output || stdio)) {
+        optimize(argv[optind], output);
+    } else if (optind < argc) {
+        for (int i = optind; i < argc; ++i) {
+            optimize(argv[i], argv[i]);
+        }
+    } else {
+        optimize(NULL, output);
+    }
+
+    return EX_OK;
+}