c - 用 C 代码翻转图像

Question

我需要能够通过操作 png 文件中的像素在 c 中水平翻转图像。尽管我尝试过，但在测试时，我的算法什么也没做。我还需要能够垂直执行此操作，但这是我的水平翻转代码:

void flip_horizontal( uint8_t array[], unsigned int cols, unsigned int rows ) {
    unsigned int left = 0;
    unsigned int right = cols;

    for(int r = 0; r < rows; r++){  
        while(left != right && right > left){
            int temp = array[r * cols + left];
            array[(r * cols) + left] = array[(r * cols) + cols - right];
            array[(r * cols) + cols - right] = temp;
            right--;
            left++;
        }
    }
}

Answer 1

您忘记在处理第一行后重置 left 和 right。

void flip_horizontal( uint8_t array[], unsigned int cols, unsigned int rows ) {
    unsigned int left = 0;
    unsigned int right = cols;

    for(int r = 0; r < rows; r++){  
        while(left != right && right > left){
            int temp = array[r * cols + left];
            array[(r * cols) + left] = array[(r * cols) + cols - right];
            array[(r * cols) + cols - right] = temp;
            right--;
            left++;
        }

        // Reset left and right after processing a row.
        left = 0;
        right = cols;
    }
}

更新

您计算的索引有误。看看下面这行。

            array[(r * cols) + left] = array[(r * cols) + cols - right];

当 left = 0, right = cols,

(r * cols) + left == (r * cols) + cols - right

当left = n，right = cols - n，并且仍然

(r * cols) + left == (r * cols) + cols - right

这就是为什么您看不到图像有任何变化的原因。

尝试:

void flip_horizontal( uint8_t array[], unsigned int cols, unsigned int rows ) {
    unsigned int left = 0;
    unsigned int right = cols-1;

    for(int r = 0; r < rows; r++){  
        while(left != right && right > left){
            int index1 = r * cols + left;
            int index2 = r * cols + right;

            int temp = array[index1];
            array[index1] = array[index2];
            array[index2] = temp;
            right--;
            left++;
        }

        // Reset left and right after processing a row.
        left = 0;
        right = cols-1;
    }
}