BMP Image padding in C from scratch

I am trying to write a small image processing app in C. Currently I am writing a function thats adds a padding to the image. When padding is even, everything works fine image has given amount of padding that wraps the image. If padding is odd image gets corrupted.

void _add_padding(struct bmp_image* image,int padding){
    //construct new images resolution with added padding.
    int new_height=image->header.height+(padding*2);
    int new_width=image->header.width+(padding*2);
    //allocate new image to the memory.
    struct pixel** output_pixels=(struct pixel**)malloc(new_height*sizeof(struct pixel*));
    for(int i=0;i<new_height;i++){
        output_pixels[i]=malloc(new_width*sizeof(struct pixel));
    }
    //initialize new image with all zeros.
    int new_colour=255;
    for(int i=0;i<new_height;i++){
        for(int j=0;j<new_width;j++){
            output_pixels[i][j].red=new_colour;
            output_pixels[i][j].green=new_colour;
            output_pixels[i][j].blue=new_colour;
        }
    }
    for(int i=padding;i<image->header.height+padding;i++){
        for(int j=padding;j<image->header.width+padding;j++){
            output_pixels[i][j].red=image->pixels[i-padding][j-padding].red;
            output_pixels[i][j].green=image->pixels[i-padding][j-padding].green;
            output_pixels[i][j].blue=image->pixels[i-padding][j-padding].blue;
        }
    }
    image->header.height=new_height;
    image->header.width=new_width;
    for(int i=0;i<image->header.height-2*padding;i++){
        free(image->pixels[i]);
    }
    free(image->pixels);
    image->pixels=output_pixels;
}

The image output if given padding is even: even padding img

The image output if given padding is odd: odd padding img

I am aware the problem is probably in these lines:

for(int i=padding;i<image->header.height+padding;i++){
    for(int j=padding;j<image->header.width+padding;j++){
       output_pixels[i][j].red=image->pixels[i-padding][j-padding].red;
       output_pixels[i][j].green=image->pixels[i-padding][j-padding].green;
       output_pixels[i][j].blue=image->pixels[i-padding][j-padding].blue;
    }
}

I've tried tinkering with the algorithm but this version (even though it produces trash half of the time) still comes as the correct algorithm for the job.

Edit: Solved the problem. Problem was the 4 byte alignment as mentioned below. The reason why even numbers would always work whether they are aligned with 4 bytes or not was simply the result of padding being added to each side of the image so thats a guarenteed multiplication by 2. Since even numbers are -obviously- even, they contain at least a 2 in them so that makes them automaticaly alligned by 4.

Hint:

You probably fell in the old Windows Bitmap trap: every row must be aligned on a 4 bytes boundary, so the row pitch must be a multiple of 4.