使用最近邻放大图像

Question

我一直在尝试让我的程序放大图像。我在为缩放图像分配新空间时遇到了一些问题，但我认为它已修复。我遇到的问题是，当我试图从临时内存持有人发回我的图像时，程序崩溃了。

加载的图像放置在我的struct Image. 像素位于 中 img->pixels，高度为img->height，宽度为img->width。但是我不知道为什么当我将像素从我的转移tmp2 struct到我的img struct时候程序会崩溃，而当我做相反的事情时它不会崩溃。这是代码：

void makeBigger(Image *img, int scale) {

    Image *tmp2;
    tmp2 = (Image*)malloc(sizeof(Image));
    tmp2->height = img->height*scale;
    tmp2->width = img->width*scale;

    tmp2->pixels = (Pixel**)malloc(sizeof(Pixel*)*tmp2->height);
    for (unsigned int i = 0; i < img->height; i++)
    {
        tmp2->pixels[i] = (Pixel*)malloc(sizeof(Pixel)*tmp2->width);
        for (unsigned int j = 0; j < img->width; j++)
        {
            tmp2->pixels[i][j] = img->pixels[i][j];
        }
    }
    free(img->pixels);

    //scaling up the struct's height and width
    img->height *= scale;
    img->width *= scale;

    img->pixels = (Pixel**)malloc(sizeof(Pixel*)*img->height);
    for (unsigned int i = 0; i < tmp2->height; i++)
    {
        img->pixels[i] = (Pixel*)malloc(sizeof(Pixel)*img->width);
        for (unsigned int j = 0; j < tmp2->width; j++)
        {
            img->pixels[i][j] = tmp2->pixels[i+i/2][j+j/2];
        }
    }
}

如果您对如何使最近邻方法起作用有任何想法，我会很高兴。

编辑：我正在尝试裁剪内部矩形，以便将其放大（缩放）。

Image *tmp = (Image*)malloc(sizeof(Image));
tmp->height = img->height / 2;
tmp->width = img->width / 2;

tmp->pixels = (Pixel**)malloc(sizeof(Pixel*) * tmp->height);
for (unsigned i = img->height / 4 - 1; i < img->height - img->height / 4; i++) {
    tmp->pixels[i] = (Pixel*)malloc(sizeof(Pixel) * tmp->width);
    for (unsigned j = img->width / 4; j < img->width - img->width / 4; j++) {
        tmp->pixels[i][j] = img->pixels[i][j];
    }
}

for (unsigned i = 0; i < img->height; i++) {
    free(img->pixels[i]);
}
free(img->pixels);

img->height = tmp->height;
img->width = tmp->width;
img->pixels = tmp->pixels;
free(tmp);

Answer 1

我看到你把事情复杂化了（例如在图像上走两次）。
这是代码（我正在发布整个程序 - 我对Pixel和Image做出的假设可能与您拥有的不匹配），但是如果您复制/粘贴makeBigger它应该在您的代码OOTB 中工作：

代码00.c：

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

typedef uint32_t Pixel;

typedef struct {
    uint32_t width, height;
    Pixel **pixels;
} Image;


void makeBigger(Image *img, int scale) {
    uint32_t i = 0, j = 0;
    Image *tmp = (Image*)malloc(sizeof(Image));
    tmp->height = img->height * scale;
    tmp->width = img->width * scale;

    tmp->pixels = (Pixel**)malloc(sizeof(Pixel*) * tmp->height);
    for (i = 0; i < tmp->height; i++) {
        tmp->pixels[i] = (Pixel*)malloc(sizeof(Pixel) * tmp->width);
        for (j = 0; j < tmp->width; j++) {
            tmp->pixels[i][j] = img->pixels[i / scale][j / scale];
        }
    }

    for (i = 0; i < img->height; i++)
        free(img->pixels[i]);
    free(img->pixels);

    img->width = tmp->width;
    img->height = tmp->height;
    img->pixels = tmp->pixels;
    free(tmp);
}


void printImage(Image *img) {
    printf("Width: %d, Height: %d\n", img->width, img->height);
    for (uint32_t i = 0; i < img->height; i++) {
        for (uint32_t j = 0; j < img->width; j++)
            printf("%3d", img->pixels[i][j]);
        printf("\n");
    }
    printf("\n");
}


int main() {
    uint32_t i = 0, j = 0, k = 1;
    Image img;
    // Initialize the image
    img.height = 2;
    img.width = 3;
    img.pixels = (Pixel**)malloc(sizeof(Pixel*) * img.height);
    for (i = 0; i < img.height; i++) {
        img.pixels[i] = (Pixel*)malloc(sizeof(Pixel) * img.width);
        for (j = 0; j < img.width; j++)
            img.pixels[i][j] = k++;
    }

    printImage(&img);
    makeBigger(&img, 2);
    printImage(&img);

    // Destroy the image
    for (i = 0; i < img.height; i++)
        free(img.pixels[i]);
    free(img.pixels);

    printf("\nDone.\n");
    return 0;
}

注释（与makeBigger相关 - 旨在替换作为参数给出的图像内容）：

• 构建一个临时图像作为放大的图像
• 只遍历临时图像一次（在我们分配它们时填充其像素）；要保持对原始图像的缩放并确保将适当的像素“复制”到新图像中，只需将索引除以缩放因子即可：tmp->pixels[i][j] = img->pixels[i / scale][j / scale]
• 释放原始图像内容：由于每个像素行都被malloc ed，它也应该是free d（free(img->pixels);单独会产生内存泄漏）
• 存储临时图像内容（到原来的），然后释放它

输出：

[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q041861274]> ~/sopr.sh
*** Set shorter prompt to better fit when pasted in StackOverflow (or other) pages ***

[064bit prompt]> ls
code00.c
[064bit prompt]> gcc -o code00.exe code00.c
[064bit prompt]> ./code00.exe
Width: 3, Height: 2
  1  2  3
  4  5  6

Width: 6, Height: 4
  1  1  2  2  3  3
  1  1  2  2  3  3
  4  4  5  5  6  6
  4  4  5  5  6  6


Done.