NightFocus

What it is

Simple python package for automated focus optimization of astrophotography image patches.

How to use it

1. create a sublcass of Camera for your camera. It must implement the take_picture method:

from nightfocus.camera import Camera

class MyCamera(Camera):
    def take_picture(self, focus: int) -> np.ndarray:
        raise NotImplementedError

2. perform focus optimization:

from nightfocus import optimize_focus

best_focus, _ = optimize_focus(camera, bounds=(0, 100))

Under the hood

NightFocus uses Bayesian optimization to find the best focus position. The default metric used is the tenengrad focus measure:

def tenengrad(image: np.ndarray, ksize: int = 3) -> float:
    """
    Tenengrad focus measure based on gradient magnitude.
    Works well for star images and is computationally efficient.
    """
    if len(image.shape) == 3:
        gray = cv2.cvtColor(image, cv2.COLOR_RGB2GRAY)
    else:
        gray = image

    gx = cv2.Sobel(gray, cv2.CV_64F, 1, 0, ksize=ksize)
    gy = cv2.Sobel(gray, cv2.CV_64F, 0, 1, ksize=ksize)
    return float(np.mean(gx**2 + gy**2))

Other metrics are available in the nightfocus.focus_metrics module:

from nightfocus.focus_metrics import FOCUS_MEASURES

FOCUS_MEASURES = {
    "tenengrad": tenengrad,
    "modified_laplacian": modified_laplacian,
    "normalized_variance": normalized_variance,
    "spectral_energy": spectral_energy,
    "brenner_gradient": brenner_gradient,
    "threshold_count": threshold_count,
    "fast_entropy": fast_entropy,
    "wavelet_measure": wavelet_measure,
}

How we know it works

It could find the correct focus when running on the datasets located in the images folder. A dataset file corresponds to a corresponding tiff image on which increasing values of blur where applied.

Command Line Interface

NightFocus includes a CLI for common tasks:

nightfocus --help

It provides this commands:

• crops: Create random crops from an image.
• dataset: Generate blurred dataset from TIFF files with increasing blur.
• evaluate: Evaluate focus scoring on a dataset.
• evaluate-directory: Evaluate focus scoring on a directory of images.
• evaluate-metrics: Evaluate multiple focus metrics on a dataset and print results.
• view: View images from a dataset file with their focus values.

Installation

pip install nightfocus

Author

Vincent Berenz, Max Planck Institute for Intelligent Systems, Tuebingen, Germany