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• moviepy black border around png when compositing into an MP4

  27 août 2022, par OneWorld

  compositing a png into an MP4 video creates a black border around the edge.

  


  This is using moviepy 1.0.0

  


  Code below reproduces the MP4 with the attached red text png.

  


  

  


  import numpy as np
import moviepy.editor as mped
def composite_txtpng_on_colour():
    bg_color = mped.ColorClip(size=[400, 300], color=np.array([0, 255, 0]).astype(np.uint8),
                          duration=2).set_position((0, 0))
    text_png_postition = [5, 5]
    text_png = mped.ImageClip("./txtpng.png", duration=3).set_position((text_png_postition))

    canvas_size = bg_color.size
    stacked_clips = mped.CompositeVideoClip([bg_color, text_png], size=canvas_size).set_duration(2)
    stacked_clips.write_videofile('text_with_black_border_video.mp4', fps=24)

composite_txtpng_on_colour()


  


  The result is an MP4 that can be played in VLC player. A screenshot of the black edge can be seen below :-

  


  

  


  Any suggestions to remove the black borders would be much appreciated.

  


  Update : It looks like moviepy does a blit instead of alpha compositing.

  


  def blit(im1, im2, pos=None, mask=None, ismask=False):
    """ Blit an image over another.  Blits ``im1`` on ``im2`` as position ``pos=(x,y)``, using the
    ``mask`` if provided. If ``im1`` and ``im2`` are mask pictures
    (2D float arrays) then ``ismask`` must be ``True``.
    """
    if pos is None:
        pos = [0, 0]

    # xp1,yp1,xp2,yp2 = blit area on im2
    # x1,y1,x2,y2 = area of im1 to blit on im2
    xp, yp = pos
    x1 = max(0, -xp)
    y1 = max(0, -yp)
    h1, w1 = im1.shape[:2]
    h2, w2 = im2.shape[:2]
    xp2 = min(w2, xp + w1)
    yp2 = min(h2, yp + h1)
    x2 = min(w1, w2 - xp)
    y2 = min(h1, h2 - yp)
    xp1 = max(0, xp)
    yp1 = max(0, yp)

    if (xp1 >= xp2) or (yp1 >= yp2):
        return im2

    blitted = im1[y1:y2, x1:x2]

    new_im2 = +im2

    if mask is None:
        new_im2[yp1:yp2, xp1:xp2] = blitted
    else:
        mask = mask[y1:y2, x1:x2]
        if len(im1.shape) == 3:
            mask = np.dstack(3 * [mask])
        blit_region = new_im2[yp1:yp2, xp1:xp2]
        new_im2[yp1:yp2, xp1:xp2] = (1.0 * mask * blitted + (1.0 - mask) * blit_region)
    
    return new_im2.astype('uint8') if (not ismask) else new_im2


  


  and so, Rotem is right.

  


  new_im2[yp1:yp2, xp1:xp2] = (1.0 * mask * blitted + (1.0 - mask) * blit_region)


  


  is

  


  (alpha * img_rgb + (1.0 - alpha) * bg)


  


  and this is how moviepy composites. And this is why we see black at the edges.

  


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