RandomToneCurve

Description

Randomly change the relationship between bright and dark areas of the image by manipulating its tone curve.

    This transform applies a random S-curve to the image's tone curve, adjusting the brightness and contrast
    in a non-linear manner. It can be applied to the entire image or to each channel separately.

    Args:
        scale (float): Standard deviation of the normal distribution used to sample random distances
            to move two control points that modify the image's curve. Values should be in range [0, 1].
            Higher values will result in more dramatic changes to the image. Default: 0.1
        per_channel (bool): If True, the tone curve will be applied to each channel of the input image separately,
            which can lead to color distortion. If False, the same curve is applied to all channels,
            preserving the original color relationships. Default: False
        p (float): Probability of applying the transform. Default: 0.5

    Targets:
        image

    Image types:
        uint8, float32

    Number of channels:
        Any

    Note:
        - This transform modifies the image's histogram by applying a smooth, S-shaped curve to it.
        - The S-curve is defined by moving two control points of a quadratic Bézier curve.
        - When per_channel is False, the same curve is applied to all channels, maintaining color balance.
        - When per_channel is True, different curves are applied to each channel, which can create color shifts.
        - This transform can be used to adjust image contrast and brightness in a more natural way than linear
            transforms.
        - The effect can range from subtle contrast adjustments to more dramatic "vintage" or "faded" looks.

    Mathematical Formulation:
        1. Two control points are randomly moved from their default positions (0.25, 0.25) and (0.75, 0.75).
        2. The new positions are sampled from a normal distribution: N(μ, σ²), where μ is the original position
        and alpha is the scale parameter.
        3. These points, along with fixed points at (0, 0) and (1, 1), define a quadratic Bézier curve.
        4. The curve is applied as a lookup table to the image intensities:
           new_intensity = curve(original_intensity)

    Examples:
        >>> import numpy as np
        >>> import albumentations as A
        >>> image = np.random.randint(0, 256, (100, 100, 3), dtype=np.uint8)

        # Apply a random tone curve to all channels together
        >>> transform = A.RandomToneCurve(scale=0.1, per_channel=False, p=1.0)
        >>> augmented_image = transform(image=image)['image']

        # Apply random tone curves to each channel separately
        >>> transform = A.RandomToneCurve(scale=0.2, per_channel=True, p=1.0)
        >>> augmented_image = transform(image=image)['image']

    References:
        - "What Else Can Fool Deep Learning? Addressing Color Constancy Errors on Deep Neural Network Performance"
          by Mahmoud Afifi and Michael S. Brown, ICCV 2019.
        - Bézier curve: https://en.wikipedia.org/wiki/B%C3%A9zier_curve#Quadratic_B%C3%A9zier_curves
        - Tone mapping: https://en.wikipedia.org/wiki/Tone_mapping
    

Parameters

• scale: float (default: 0.1)
• per_channel: bool (default: false)
• p: float (default: 0.5)

Targets

• Image