279 lines
14 KiB
C
279 lines
14 KiB
C
#include "DitherPixels.h"
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#include <math.h>
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#include <stdlib.h>
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static inline float clamp01(float v) { return v < 0 ? 0 : v > 1 ? 1 : v; }
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// Density darkens (positive) or lightens as a gamma, so black and white stay put; contrast pivots on mid gray.
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static inline float adjust_tone(float v, float gamma, float contrast) {
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v = powf(clamp01(v), gamma);
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return clamp01((v - 0.5f) * contrast + 0.5f);
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}
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// One error-diffusion kernel: neighbors to the right on this row and below, with their weights over `divisor`.
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typedef struct { int dx, dy, weight; } Tap;
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typedef struct { const Tap *taps; int count; float divisor; } Kernel;
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static const Tap atkinson[] = { {1,0,1}, {2,0,1}, {-1,1,1}, {0,1,1}, {1,1,1}, {0,2,1} };
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static const Tap floyd[] = { {1,0,7}, {-1,1,3}, {0,1,5}, {1,1,1} };
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// Atkinson passes on only six eighths of the error, which is what gives the Mac's crisp, contrasty look.
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static Kernel kernel_for(int style) {
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return style == DITHER_ATKINSON ? (Kernel){ atkinson, 6, 8 } : (Kernel){ floyd, 4, 16 };
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}
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static inline float quantize(float v, int levels) {
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float steps = (float)(levels - 1);
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return roundf(clamp01(v) * steps) / steps;
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}
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// Diffuses each plane in serpentine order, so the error's drift doesn't streak to one side.
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static void diffuse(float *plane, const uint8_t *alpha, size_t width, size_t height, const DitherParams *p) {
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Kernel k = kernel_for(p->style);
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for (size_t y = 0; y < height; ++y) {
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int reverse = (int)(y & 1);
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for (size_t i = 0; i < width; ++i) {
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size_t x = reverse ? width - 1 - i : i;
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size_t at = y * width + x;
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if (!alpha[at]) continue;
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float old = plane[at], q = quantize(old, p->levels);
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plane[at] = q;
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float error = (old - q) * p->diffusion / k.divisor;
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for (int t = 0; t < k.count; ++t) {
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long nx = (long)x + (reverse ? -k.taps[t].dx : k.taps[t].dx), ny = (long)y + k.taps[t].dy;
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if (nx < 0 || nx >= (long)width || ny >= (long)height) continue;
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plane[(size_t)ny * width + (size_t)nx] += error * (float)k.taps[t].weight;
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}
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}
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}
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}
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static const uint8_t bayer8[64] = {
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0, 32, 8, 40, 2, 34, 10, 42, 48, 16, 56, 24, 50, 18, 58, 26,
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12, 44, 4, 36, 14, 46, 6, 38, 60, 28, 52, 20, 62, 30, 54, 22,
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3, 35, 11, 43, 1, 33, 9, 41, 51, 19, 59, 27, 49, 17, 57, 25,
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15, 47, 7, 39, 13, 45, 5, 37, 63, 31, 55, 23, 61, 29, 53, 21,
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};
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// The ordered threshold for a pixel, in [0, 1). Smaller Bayer matrices are the top-left corners of the 8 × 8 one,
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// rescaled, which is how the recursive construction nests them.
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static inline float ordered_threshold(int style, size_t x, size_t y) {
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switch (style) {
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case DITHER_BAYER_2: { static const uint8_t m[4] = { 0, 2, 3, 1 }; return ((float)m[(y & 1) * 2 + (x & 1)] + 0.5f) / 4; }
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case DITHER_BAYER_4: {
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static const uint8_t m[16] = { 0, 8, 2, 10, 12, 4, 14, 6, 3, 11, 1, 9, 15, 7, 13, 5 };
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return ((float)m[(y & 3) * 4 + (x & 3)] + 0.5f) / 16;
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}
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default: return ((float)bayer8[(y & 7) * 8 + (x & 7)] + 0.5f) / 64;
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}
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}
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static inline float ordered(float v, float threshold, int levels) {
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float steps = (float)(levels - 1);
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float q = floorf(clamp01(v) * steps + threshold);
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return (q > steps ? steps : q) / steps;
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}
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// How much of a halftone cell a point must be covered by before it's marked, for each screen shape. `u` and `v`
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// run from −0.5 to 0.5 across the cell; the shapes grow from its middle as coverage rises.
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static inline float spot(int style, float u, float v) {
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float au = fabsf(u), av = fabsf(v);
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switch (style) {
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case DITHER_DOTS: return 3.14159265f * (u * u + v * v);
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case DITHER_LINES: return av * 2;
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default: return au + av;
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}
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}
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// Old Mac fill patterns, 8 × 8, one byte per row with the leftmost pixel in the top bit, from sparsest to fullest.
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static const uint8_t patterns[][8] = {
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{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
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{ 0x80, 0x00, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00 },
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{ 0x88, 0x00, 0x22, 0x00, 0x88, 0x00, 0x22, 0x00 },
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{ 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 },
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{ 0x88, 0x22, 0x88, 0x22, 0x88, 0x22, 0x88, 0x22 },
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{ 0x00, 0xFF, 0x00, 0x00, 0x00, 0xFF, 0x00, 0x00 },
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{ 0x11, 0x22, 0x44, 0x88, 0x11, 0x22, 0x44, 0x88 },
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{ 0xAA, 0x00, 0xAA, 0x00, 0xAA, 0x00, 0xAA, 0x00 },
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{ 0x88, 0x55, 0x22, 0x55, 0x88, 0x55, 0x22, 0x55 },
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{ 0xFF, 0x80, 0x80, 0x80, 0xFF, 0x08, 0x08, 0x08 },
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{ 0xAA, 0x55, 0xAA, 0x55, 0xAA, 0x55, 0xAA, 0x55 },
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{ 0x81, 0x42, 0x24, 0x18, 0x18, 0x24, 0x42, 0x81 },
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{ 0x77, 0xAA, 0xDD, 0xAA, 0x77, 0xAA, 0xDD, 0xAA },
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{ 0xEE, 0xDD, 0xBB, 0x77, 0xEE, 0xDD, 0xBB, 0x77 },
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{ 0x77, 0xFF, 0xDD, 0xFF, 0x77, 0xFF, 0xDD, 0xFF },
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{ 0x7F, 0xFF, 0xFF, 0xFF, 0xF7, 0xFF, 0xFF, 0xFF },
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{ 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF },
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};
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static const int patternCount = (int)(sizeof patterns / sizeof patterns[0]);
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static inline void write_pixel(uint8_t *px, float r, float g, float b) {
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float a = (float)px[3] / 255.0f;
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px[0] = (uint8_t)lroundf(clamp01(r) * a * 255.0f);
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px[1] = (uint8_t)lroundf(clamp01(g) * a * 255.0f);
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px[2] = (uint8_t)lroundf(clamp01(b) * a * 255.0f);
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}
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int dither_apply(uint8_t *rgba, size_t width, size_t height, size_t stride, const DitherParams *p) {
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size_t count = width * height;
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if (!count) return 1;
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int planes = p->originalColors ? 3 : 1;
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float *tone = malloc(count * sizeof(float) * (size_t)planes);
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uint8_t *alpha = malloc(count);
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// The image's own colors, unadjusted: halftone dots and glyphs take them in Original mode.
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float *source = p->originalColors ? malloc(count * sizeof(float) * 3) : NULL;
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if (!tone || !alpha || (p->originalColors && !source)) { free(tone); free(alpha); free(source); return 0; }
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float gamma = exp2f(p->density * 1.5f);
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float contrast = p->contrast >= 0 ? 1.0f / (1.0f - 0.95f * p->contrast) : 1.0f + p->contrast;
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for (size_t y = 0; y < height; ++y) {
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const uint8_t *row = rgba + y * stride;
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for (size_t x = 0; x < width; ++x) {
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const uint8_t *px = row + x * 4;
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size_t at = y * width + x;
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alpha[at] = px[3];
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float r = 0, g = 0, b = 0;
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if (px[3]) {
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float scale = 1.0f / (float)px[3];
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r = px[0] * scale; g = px[1] * scale; b = px[2] * scale;
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}
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if (p->originalColors) {
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tone[at] = adjust_tone(r, gamma, contrast);
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tone[count + at] = adjust_tone(g, gamma, contrast);
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tone[2 * count + at] = adjust_tone(b, gamma, contrast);
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source[at * 3] = r; source[at * 3 + 1] = g; source[at * 3 + 2] = b;
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} else {
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tone[at] = adjust_tone(0.2126f * r + 0.7152f * g + 0.0722f * b, gamma, contrast);
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}
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}
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}
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float dark[3] = { p->dark[0] / 255.0f, p->dark[1] / 255.0f, p->dark[2] / 255.0f };
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float light[3] = { p->light[0] / 255.0f, p->light[1] / 255.0f, p->light[2] / 255.0f };
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int style = p->style;
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int levels = p->levels < 2 ? 2 : p->levels > 16 ? 16 : p->levels;
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if (style <= DITHER_BAYER_8) {
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// Diffusion and ordered dithering: each plane is quantized to `levels` tones, then mapped to colors.
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if (style <= DITHER_FLOYD_STEINBERG) {
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DitherParams local = *p;
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local.levels = levels;
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for (int c = 0; c < planes; ++c) diffuse(tone + (size_t)c * count, alpha, width, height, &local);
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} else {
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for (int c = 0; c < planes; ++c) {
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float *plane = tone + (size_t)c * count;
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for (size_t y = 0; y < height; ++y)
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for (size_t x = 0; x < width; ++x) {
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size_t at = y * width + x;
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if (alpha[at]) plane[at] = ordered(plane[at], ordered_threshold(style, x, y), levels);
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}
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}
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}
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for (size_t y = 0; y < height; ++y) {
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uint8_t *row = rgba + y * stride;
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for (size_t x = 0; x < width; ++x) {
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size_t at = y * width + x;
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if (!alpha[at]) continue;
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if (p->originalColors) {
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write_pixel(row + x * 4, tone[at], tone[count + at], tone[2 * count + at]);
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} else {
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float t = tone[at];
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write_pixel(row + x * 4, dark[0] + (light[0] - dark[0]) * t, dark[1] + (light[1] - dark[1]) * t,
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dark[2] + (light[2] - dark[2]) * t);
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}
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}
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}
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} else {
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// Marks (halftone shapes, patterns, glyphs) cover as much of each spot as the tone calls for. On light, they
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// stand for darkness and are drawn in the dark color; light on dark, the reverse.
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float *marks = p->originalColors ? malloc(count * sizeof(float)) : tone;
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if (!marks) { free(tone); free(alpha); free(source); return 0; }
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if (p->originalColors)
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for (size_t i = 0; i < count; ++i)
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marks[i] = 0.2126f * tone[i] + 0.7152f * tone[count + i] + 0.0722f * tone[2 * count + i];
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int cell = p->cell < 2 ? 2 : p->cell;
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float cosA = cosf(p->angle), sinA = sinf(p->angle);
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float *ink = p->lightOnDark ? light : dark, *paper = p->lightOnDark ? dark : light;
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// Glyphs: each cell shares one, picked from the cell's average tone, worked out once per cell.
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size_t columns = (width + (size_t)cell - 1) / (size_t)cell, cellRows = (height + (size_t)cell - 1) / (size_t)cell;
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int *picked = NULL;
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if (style == DITHER_GLYPHS && p->glyphCount > 0) {
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picked = malloc(columns * cellRows * sizeof(int));
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if (!picked) { if (marks != tone) free(marks); free(tone); free(alpha); free(source); return 0; }
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for (size_t row = 0; row < cellRows; ++row)
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for (size_t column = 0; column < columns; ++column) {
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float sum = 0; int n = 0;
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for (size_t yy = row * (size_t)cell; yy < (row + 1) * (size_t)cell && yy < height; ++yy)
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for (size_t xx = column * (size_t)cell; xx < (column + 1) * (size_t)cell && xx < width; ++xx) {
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size_t i = yy * width + xx;
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if (alpha[i]) { sum += marks[i]; ++n; }
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}
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float t = n ? sum / (float)n : 1;
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float wanted = (p->lightOnDark ? t : 1 - t) * p->glyphCoverage[p->glyphCount - 1];
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int best = 0;
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float bestDistance = 2;
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for (int g = 0; g < p->glyphCount; ++g) {
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float d = fabsf(p->glyphCoverage[g] - wanted);
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if (d < bestDistance) { bestDistance = d; best = g; }
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}
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picked[row * columns + column] = best;
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}
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}
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// Original colors: marks take the pixel's own color, on black (light on dark) or white.
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float paperOriginal = p->lightOnDark ? 0.0f : 1.0f;
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for (size_t y = 0; y < height; ++y) {
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uint8_t *row = rgba + y * stride;
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for (size_t x = 0; x < width; ++x) {
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size_t at = y * width + x;
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if (!alpha[at]) continue;
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float amount;
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if (picked) {
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int glyph = picked[(y / (size_t)cell) * columns + x / (size_t)cell];
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amount = p->glyphs[(size_t)glyph * (size_t)(cell * cell) + (y % (size_t)cell) * (size_t)cell + x % (size_t)cell] / 255.0f;
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} else if (style == DITHER_PATTERNS) {
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float t = marks[at];
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float coverage = p->lightOnDark ? t : 1 - t;
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int index = (int)lroundf(coverage * (float)(patternCount - 1));
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amount = (patterns[index][y & 7] >> (7 - (x & 7))) & 1;
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} else {
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float fx = (float)x + 0.5f, fy = (float)y + 0.5f;
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float u = (fx * cosA + fy * sinA) / (float)cell, v = (-fx * sinA + fy * cosA) / (float)cell;
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u -= floorf(u) + 0.5f; v -= floorf(v) + 0.5f;
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float t = marks[at];
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amount = (p->lightOnDark ? t : 1 - t) > spot(style, u, v) ? 1 : 0;
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}
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if (p->originalColors) {
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const float *s = source + at * 3;
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write_pixel(row + x * 4, paperOriginal + (s[0] - paperOriginal) * amount,
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paperOriginal + (s[1] - paperOriginal) * amount, paperOriginal + (s[2] - paperOriginal) * amount);
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} else {
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write_pixel(row + x * 4, paper[0] + (ink[0] - paper[0]) * amount, paper[1] + (ink[1] - paper[1]) * amount,
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paper[2] + (ink[2] - paper[2]) * amount);
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}
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}
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}
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free(picked);
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if (marks != tone) free(marks);
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}
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free(tone); free(alpha); free(source);
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return 1;
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}
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void dither_dots(uint8_t *rgba, size_t width, size_t height, size_t stride, int block, const uint8_t *gap) {
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if (block < 2) return;
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float radius = (float)block * 0.42f, middle = (float)block / 2;
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for (size_t y = 0; y < height; ++y) {
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uint8_t *row = rgba + y * stride;
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float dy = (float)(y % (size_t)block) + 0.5f - middle;
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for (size_t x = 0; x < width; ++x) {
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uint8_t *px = row + x * 4;
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if (!px[3]) continue;
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float dx = (float)(x % (size_t)block) + 0.5f - middle;
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float cover = clamp01(radius - sqrtf(dx * dx + dy * dy) + 0.5f);
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if (cover >= 1) continue;
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for (int c = 0; c < 3; ++c)
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px[c] = (uint8_t)lroundf((float)px[c] * cover + (float)gap[c] * (float)px[3] / 255.0f * (1 - cover));
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}
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}
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}
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