Sure! Here's a test case generator for the given JPEG Compression problem:

```python
import random

def tcgen():
    test_cases = []
    
    while True:
        N = random.randint(0, 9)
        if N == 0:
            test_cases.append(N)
            break
        test_cases.append(N)
    
    return test_cases

# Example usage:
test_cases = tcgen()
for i, N in enumerate(test_cases):
    if N == 0:
        print(f'Test Case {i+1}: End of Input')
    else:
        print(f'Test Case {i+1}: N = {N}')
```

Explanation:

1. **Random Test Case Generation**:
    - We generate random integers \(N\) between 0 and 9, which simulate the matrix size.
    - We continue generating values until we get a zero, which signals the end of input.

2. **Output Format**:
    - For each test case, we print the corresponding \(N\) value.
    - When \(N = 0\), we denote it as the end of input.

3. **Complete Test Case Output**:
    - You would need to implement the logic to produce the zigzag matrix for each \(N\) value in your main problem-solving code separately. The generator here just provides random test cases.

This should help you generate random test cases for the given problem. If you need further assistance or additional functionality, feel free to ask!