Otaku Strokes Extractor v3 (OSE3)

概述

很久很久以前（大约20年7月）写的一个奇奇怪怪的算法，当时的目的是为了从一堆动漫图片中获取其线稿用于描画练习
但是当时还没有现如今流行的各种大模型，根本做不到快速的本地抽出，所以就去尝试了解了一下一些简单的图像处理库
（当时还在用7300HQ老U，做不到基于纯图形或者推测的处理），后来就想了个办法，用色容差和反色+灰度来解决这个问题，出来的效果也暂且不算难看，用于描画练习则是绰绰有余了。
最近翻出来了当时的V1和V2版本代码，仔细阅读后发现写的属实非常烂，就直接尝试对其进行了直接的整体重构
以下为代码，编译时请携带好STB的头，用clang -Os -o OSE3 OSE3.C -lm来执行编译

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"

#define GRAYSCALE_RED_WEIGHT 0.3
#define GRAYSCALE_GREEN_WEIGHT 0.59
#define GRAYSCALE_BLUE_WEIGHT 0.11

void imgProcessGray(uint8_t *s, int sx, int sy, int stride, uint8_t *p, int gstride)
{
    for (int y=0; y<sy; y++) {
        for (int x=0; x<sx; x++) {
            p[x] = GRAYSCALE_RED_WEIGHT * s[x*3+0] + GRAYSCALE_GREEN_WEIGHT * s[x*3+1] + GRAYSCALE_BLUE_WEIGHT *s[x*3+2];
        }
        s += stride*3;
        p += gstride;
    }
}

void imgProcessDilate(uint8_t *s, int w, int h, int k, uint8_t *p)
{
    for (int y=1; y<h-1; y++) {
        for (int x=1; x<w-1; x++) {
            uint8_t uc = s[ (y+0)*w + (x+0) ];
            uint8_t ua = s[ (y-1)*w + (x+0) ];
            uint8_t ub = s[ (y+1)*w + (x+0) ];
            uint8_t ul = s[ (y+0)*w + (x-1) ];
            uint8_t ur = s[ (y+0)*w + (x+1) ];
            uint8_t ux = 0;
            if (uc > ux) ux = uc;
            if (ua > ux) ux = ua;
            if (ub > ux) ux = ub;
            if (ul > ux) ux = ul;
            if (ur > ux) ux = ur;
            p[ y*w + x ] = ux;
        }
    }
}

void imgProcessAbsdiff(uint8_t *s, uint8_t *s2, int w, int h, uint8_t *p)
{
    for (int n=0; n<w*h; n++) {
        *p++ = abs(*s++ - *s2++);
    }
}

void imgProcessReverse(uint8_t *s, int w, int h, uint8_t *p)
{
    for (int n=0; n<w*h; n++) {
        *p++ = 255 - *s++;
    }
}

int main(int argc, char* argv[])
{
    if (argc != 2) {
        fprintf(stderr, "Otaku Strokes Extractor v3\n");
        fprintf(stderr, "Usage: %s <image_path>\n", argv[0]);
        return 1;
    }

    char *name = argv[1];

    int w, h, bpp;
    uint8_t *pixels = stbi_load(name, &w, &h, &bpp, 3);
    if (!pixels) {
        fprintf(stderr, "Failed to load image: %s\n", name);
        return 1;
    }

    uint8_t *gray = (uint8_t*) malloc(w*h*4);
    if (!gray) {
        fprintf(stderr, "Failed to allocate memory for image processing.\n");
        stbi_image_free(pixels);
        return 1;
    }

    uint8_t *dilated = gray + w*h;
    uint8_t *diff = dilated + w*h;
    uint8_t *contour = diff + w*h;

    printf("Processing %s...\n", name);
    imgProcessGray(pixels, w, h, w, gray, w);
    imgProcessDilate(gray, w, h, 5, dilated);
    imgProcessAbsdiff(gray, dilated, w, h, diff);
    imgProcessReverse(diff, w, h, contour);
    stbi_write_jpg("result.jpg", w, h, 1, contour, 0);
    printf("Done for %s !\n", name);

    free(gray);
    stbi_image_free(pixels);

    return 0;
}

Windows体验版(使用MSYS2的gcc 11.3.0链静态构建)
OSE3_x64.exe

效果

原图

线稿

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