use parameters from python launch file in node

edit

I am trying to use parameters specified in my .launch.py file, but a ParameterNotDeclaredException is thrown when accessing any parameter. Does anyone know why? I try to access the parameters like this from within my Node:

self.get_parameter('buffer_size')

Here is the launch file. I'm using Foxy and Python

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription([
        Node(
            package='blackfly_calibration',
            executable='broadcaster',
            parameters=[
                {"capture_frequency": 20.0},
                {"buffer_size": 10},
                {"image_topic": "/camera/image_raw"}
            ],
        )
    ])