c - MagickWand for C，调用 DestroyPixelWands 时出错

Question

我开始在一个简单的 C 程序中使用 ImageMagick 和 MagickWand API。现在，作为测试，我只是在帧中寻找黑色像素。这是我的代码:

int find_black_pixel(MagickWand *wand) {
    int res = 0;
    PixelIterator * iterator = NewPixelIterator(wand);
    size_t width=MagickGetImageWidth(wand);
    size_t height=MagickGetImageHeight(wand);
    PixelWand ** pixels;
    unsigned long x,y;
    unsigned int alpha;
    unsigned int red, green, blue;

    //printf("Width : %d, Height : %d\n", (int)width, (int)height);

    for (y=0; y<height; y++) {
        pixels = PixelGetNextIteratorRow(iterator, &width);
        for (x=0; x<width; x++) {

            alpha = (unsigned int) (255*PixelGetAlpha(pixels[x]));
            if (alpha == 0)
                continue;

            red = (unsigned int) (255*PixelGetRed(pixels[x]));
            green = (unsigned int) (255*PixelGetGreen(pixels[x]));
            blue = (unsigned int) (255*PixelGetBlue(pixels[x]));

            //printf("At %04ld,%04ld, alpha : %d, rgb : %d,%d,%d\n", x,y,alpha, red, green, blue);

            if ((red ==0) || (green == 0) || (blue ==0)) {

                res = 1;
                //DestroyPixelWands(pixels, width);
                goto finished_find_black_pixel;
            }

        }
        //DestroyPixelWands(pixels, (size_t)width);
    }

finished_find_black_pixel:
    DestroyPixelIterator(iterator);

    return res;
}

如果我取消注释任何 DestroyPixelWands 调用，我会得到一个断言:

test: wand/pixel-wand.c:283: DestroyPixelWands: Assertion `(*wand)->signature == 0xabacadabUL' failed.

知道为什么会发生这种情况吗？

编辑:

更多调试...甚至调用 DestroyPixelWand(pixels[0]); 也会以同样的方式失败...

Answer 1

我怀疑 pixels 不是一个单独的可破坏对象(它只是指向原始 wand 对象的指针)，并且您当前的代码没有问题，无需任何代码销毁像素。