The CWE-190 vulnerability at line 28 is caused by the use of the `atoi` function to convert the string `optarg` to an integer. 

The `atoi` function does not perform any error checking on the input string. If the string cannot be converted to an integer (for example, if it contains non-numeric characters), `atoi` will return 0. However, it does not provide any indication that an error occurred.

In this specific case, if the user provides an invalid argument for the option that corresponds to `horizSubSampling`, `atoi` will silently return 0, potentially causing the program to behave unexpectedly or produce incorrect results.

Furthermore, if the input string represents a number that is outside the range of `int`, `atoi` will also return an incorrect result, potentially causing the program to behave unexpectedly or produce incorrect results.

To fix this vulnerability, you should use a safer function like `strtol` or `strtod` that provides error checking and allows you to handle invalid input. Here is an example of how you can use `strtol` to fix the vulnerability:

```c
#include <stdlib.h>
#include <errno.h>

// ...

long value;
char *endptr;

errno = 0;
value = strtol(optarg, &endptr, 10);

if (endptr == optarg) {
    // No digits were found in the input string
    fprintf(stderr, "Invalid argument for option: %s\n", optarg);
    exit(1);
}

if (errno == ERANGE) {
    // The input string represents a number that is outside the range of long
    fprintf(stderr, "Argument for option is out of range: %s\n", optarg);
    exit(1);
}

if (*endptr != '\0') {
    // The input string contains non-numeric characters
    fprintf(stderr, "Invalid argument for option: %s\n", optarg);
    exit(1);
}

horizSubSampling = (int)value;
```

This code checks for errors when converting the input string to an integer and handles invalid input by printing an error message and exiting the program.