Subtract

mg_subtract

mg_subtract(self, color=True, filtertype=None, threshold=0.05, blur=False, curves=0.15, use_median=False, kernel_size=5, bg_img=None, bg_color='#000000', target_name=None, overwrite=True)

Renders background subtraction using ffmpeg.

Parameters:

Name	Type	Description	Default
color	bool	If False the input is converted to grayscale at the start of the process. This can significantly reduce render time. Defaults to True.	True
filtertype	str	'Regular' turns all values below threshold to 0. 'Binary' turns all values below threshold to 0, above threshold to 1. 'Blob' removes individual pixels with erosion method. Defaults to 'Regular'.	None
threshold	float	Eliminates pixel values less than given threshold. Ranges from 0 to 1. Defaults to 0.05.	0.05
blur	bool	Whether to apply a smartblur ffmpeg filter or not. Defaults to False.	False
curves	int	Apply curves and equalisation threshold filter to subtract the background. Ranges from 0 to 1. Defaults to 0.15.	0.15
use_median	bool	If True the algorithm applies a median filter on the thresholded frame-difference stream. Defaults to False.	False
kernel_size	int	Size of the median filter (if use_median=True) or the erosion filter (if filtertype='blob'). Defaults to 5.	5
bg_img	str	Path to a background image (.png) that needs to be subtracted from the video. If set to None, it uses an average image of all frames in the video. Defaults to None.	None
bg_color	str	Set the background color in the video file in hex value. Defaults to '#000000' (black).	'#000000'
target_name	str	Target output name for the subtracted video. Defaults to None.	None
overwrite	bool	Whether to allow overwriting existing files or to automatically increment target filenames to avoid overwriting. Defaults to True.	True

Returns:

Name	Type	Description
MgVideo	MgVideo	A MgVideo pointing to the subtracted video, also stored as subtract_video on the parent MgVideo

Source code in musicalgestures/_subtract.py

def mg_subtract(
        self,
        color=True,
        filtertype=None,
        threshold=0.05,
        blur=False,
        curves=0.15,
        use_median=False,
        kernel_size=5,
        bg_img=None,
        bg_color='#000000',
        target_name=None,
        overwrite=True) -> "musicalgestures.MgVideo":
    """
    Renders background subtraction using ffmpeg. 

    Args:
        color (bool, optional): If False the input is converted to grayscale at the start of the process. This can significantly reduce render time. Defaults to True.
        filtertype (str, optional): 'Regular' turns all values below `threshold` to 0. 'Binary' turns all values below `threshold` to 0, above `threshold` to 1. 'Blob' removes individual pixels with erosion method. Defaults to 'Regular'.
        threshold (float, optional): Eliminates pixel values less than given threshold. Ranges from 0 to 1. Defaults to 0.05.
        blur (bool, optional): Whether to apply a smartblur ffmpeg filter or not. Defaults to False.
        curves (int, optional): Apply curves and equalisation threshold filter to subtract the background. Ranges from 0 to 1. Defaults to 0.15.
        use_median (bool, optional): If True the algorithm applies a median filter on the thresholded frame-difference stream. Defaults to False.
        kernel_size (int, optional): Size of the median filter (if `use_median=True`) or the erosion filter (if `filtertype='blob'`). Defaults to 5.
        bg_img (str, optional): Path to a background image (.png) that needs to be subtracted from the video. If set to None, it uses an average image of all frames in the video. Defaults to None.
        bg_color (str, optional): Set the background color in the video file in hex value. Defaults to '#000000' (black). 
        target_name (str, optional): Target output name for the subtracted video. Defaults to None.
        overwrite (bool, optional): Whether to allow overwriting existing files or to automatically increment target filenames to avoid overwriting. Defaults to True.

    Returns:
        MgVideo: A MgVideo pointing to the subtracted video, also stored as `subtract_video` on the parent MgVideo
    """

    of, fex = os.path.splitext(self.filename)

    if target_name is None:
        target_name = of + '_subtracted.avi'

    if not overwrite:
        target_name = generate_outfilename(target_name)

    width, height = self.width, self.height

    if bg_img is None:
        # Render an average image of the video file for background subtraction
        bg_img = musicalgestures.MgVideo(self.filename).blend(component_mode='average').filename
    else:
        # Check if background image extension is .png or not
        pass_if_container_is(".png", bg_img)

    # Set input/output and background color to white
    cmd = ['ffmpeg', '-y', '-i', bg_img, '-i', self.filename]
    cmd_end = ['-shortest', '-pix_fmt', 'yuv420p', target_name]
    cmd_filter = f'color={bg_color}:size={width}x{height} [matte];[1:0]'

    # Set color mode
    if color == True:
        pixformat = 'gbrp'
    else:
        pixformat = 'gray'

    cmd_filter += f'format={pixformat}, split[mask][video];[0:0][mask]'

    # Set frame difference
    if filtertype is not None:
        if filtertype.lower() == 'regular':
            cmd_filter += 'blend=all_mode=difference[diff],'
        else:
            cmd_filter += 'blend=all_mode=difference,'
    else:
        cmd_filter += 'blend=all_mode=difference,'

    thresh_color = matplotlib.colors.to_hex([threshold, threshold, threshold])
    thresh_color = '0x' + thresh_color[1:]

    # Set threshold
    if filtertype is not None:
        if filtertype.lower() == 'regular':
            cmd += ['-f', 'lavfi', '-i', f'color={thresh_color},scale={width}:{height}', 
                    '-f', 'lavfi', '-i', f'color=black,scale={width}:{height}']
            cmd_filter += '[1][diff]threshold,'
        elif filtertype.lower() == 'binary':
            cmd += ['-f', 'lavfi', '-i', f'color={thresh_color},scale={width}:{height}', '-f', 'lavfi', '-i',
                    f'color=black,scale={width}:{height}', '-f', 'lavfi', '-i', f'color=white,scale={width}:{height}']
            cmd_filter += ' threshold,'
        elif filtertype.lower() == 'blob':
            # cmd_filter += 'erosion,' # erosion is always 3x3 so we will hack it with a median filter with percentile=0 which will pick minimum values
            cmd_filter += f'median=radius={kernel_size}:percentile=0,'       

    # Set median
    if use_median and (filtertype is None or filtertype.lower() != 'blob'):  # makes no sense to median-filter the eroded video
        cmd_filter += f'median=radius={kernel_size},'

    # Set curves and equalisation filtering to a range of values between 0.1 and 0.9 
    new_curves = (((curves - 0) * (0.8 - 0.1)) / (1 - 0)) + 0.1
    cmd_filter += f"curves=m='0/0 {str(round(new_curves,2))}/0 {str(round(new_curves+0.1,2))}/1 1/1',"

    # Set blur
    if blur:
        cmd_filter += 'format=gray,smartblur=1,smartblur=3,'

    cmd_filter += f'format=gray [mask];[matte][video][mask] maskedmerge, format={pixformat}' 
    cmd_filter = ['-filter_complex', cmd_filter]  
    cmd = cmd + cmd_filter + cmd_end

    ffmpeg_cmd(cmd, get_length(self.filename), pb_prefix='Subtracting background:', stream=True)

    # Save subtracted video as subtract_video for parent MgVideo. NB: not
    # `self.subtract`, which would overwrite (shadow) the bound method and
    # break any subsequent subtract() call on the same object.
    self.subtract_video = musicalgestures.MgVideo(target_name, color=color, returned_by_process=True)

    return self.subtract_video