ToGray

Description

Convert an image to grayscale and optionally replicate the grayscale channel.

    This transform first converts a color image to a single-channel grayscale image using various methods,
    then replicates the grayscale channel if num_output_channels is greater than 1.

    Args:
        num_output_channels (int): The number of channels in the output image. If greater than 1,
            the grayscale channel will be replicated. Default: 3.
        method (Literal["weighted_average", "from_lab", "desaturation", "average", "max", "pca"]):
            The method used for grayscale conversion:
            - "weighted_average": Uses a weighted sum of RGB channels (0.299R + 0.587G + 0.114B).
              Works only with 3-channel images. Provides realistic results based on human perception.
            - "from_lab": Extracts the L channel from the LAB color space.
              Works only with 3-channel images. Gives perceptually uniform results.
            - "desaturation": Averages the maximum and minimum values across channels.
              Works with any number of channels. Fast but may not preserve perceived brightness well.
            - "average": Simple average of all channels.
              Works with any number of channels. Fast but may not give realistic results.
            - "max": Takes the maximum value across all channels.
              Works with any number of channels. Tends to produce brighter results.
            - "pca": Applies Principal Component Analysis to reduce channels.
              Works with any number of channels. Can preserve more information but is computationally intensive.
        p (float): Probability of applying the transform. Default: 0.5.

    Raises:
        TypeError: If the input image doesn't have 3 channels for methods that require it.

    Note:
        - The transform first converts the input image to single-channel grayscale, then replicates
          this channel if num_output_channels > 1.
        - "weighted_average" and "from_lab" are typically used in image processing and computer vision
          applications where accurate representation of human perception is important.
        - "desaturation" and "average" are often used in simple image manipulation tools or when
          computational speed is a priority.
        - "max" method can be useful in scenarios where preserving bright features is important,
          such as in some medical imaging applications.
        - "pca" might be used in advanced image analysis tasks or when dealing with hyperspectral images.

    Image types:
        uint8, float32

    Returns:
        np.ndarray: Grayscale image with the specified number of channels.
    

Parameters

• p: float (default: 0.5)
• num_output_channels: int (default: 3)
• method: Literal['weighted_average', 'from_lab', 'desaturation', 'average', 'max', 'pca'] (default: 'weighted_average')

Targets

• Image

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