Mask not applying correctly in MoviePy v2 (works in v1 with grayscale, image but requires RGBA in v2)

[zeeshanghazanfar97]

Expected Behavior

When applying a grayscale mask to an ImageClip, areas defined by the mask should become transparent, as per MoviePy’s documentation.

Actual Behavior

In MoviePy v2, the mask appears to be overlaid on top of the image instead of making areas transparent. However, using an RGBA image as the mask makes it work, even though the documentation specifies that masks should be grayscale.

Steps and code to Reproduce the Problem

This issue occurs when using a grayscale image as a mask in MoviePy v2. Below is a minimal reproducible example:

Working Code (MoviePy v1.0.3)

from moviepy.editor import ImageClip, CompositeVideoClip

# Load the image and grayscale mask
image_clip = ImageClip("mask.png").set_duration(5)
mask_clip = ImageClip("blueDark.png", ismask=True).set_duration(5)

# Apply the mask
image_clip = image_clip.set_mask(mask_clip)

# Render with background color
video = CompositeVideoClip([image_clip], bg_color=(90, 90, 90))
video.preview()

This works as expected—areas of image_clip defined by mask_clip become transparent.

Non-Working Code (MoviePy v2)

import moviepy as mpy

# Load the image and grayscale mask
image_clip = mpy.ImageClip("mask.png").with_duration(5)
mask_clip = mpy.ImageClip("blueDark.png", is_mask=True).with_duration(5)

# Apply the mask
image_clip = image_clip.with_mask(mask_clip)

# Render with background color
video = mpy.CompositeVideoClip([image_clip], bg_color=(90, 90, 90))
video.preview()

In MoviePy v2, this does not work as expected. The mask is overlaid on top of the image instead of making parts transparent.

Workaround

Using an RGBA image as the mask instead of a grayscale image seems to make it work, despite the documentation stating that masks should be grayscale.

Used Media (attached below)

• mask.png (main image)
• blueDark.png (grayscale mask)

Specifications

• Python Version: (e.g., 3.10.6)
• MoviePy Version: 2.0.0
• Platform Name: (e.g., Windows 11, Ubuntu 22.04)
• Platform Version: MacOS

blueDark.png

mask.png

It seems like a bug since the documented behavior does not match the actual behavior. Would appreciate clarification or a fix. Thanks! 🚀