test/effects/vhs.py

# /// script
# requires-python = ">=3.10"
# dependencies = ["numpy", "opencv-python"]
# ///
"""
@effect vhs
@version 1.0.0
@author artdag

@description
VHS / Analog Video effect. Complete VHS tape simulation combining
tracking errors, color bleeding, noise, and scan line distortion.

@param tracking_error float
  @range 0 50
  @default 5
  Horizontal displacement amount. Sync to onset for glitches.

@param color_bleed int
  @range 0 20
  @default 3
  Horizontal color smearing (typical VHS artifact).

@param noise_intensity float
  @range 0 1
  @default 0.2
  Static noise amount.

@param chroma_shift int
  @range 0 15
  @default 2
  Color channel offset (VHS color alignment issues).

@param head_switching bool
  @default true
  Bottom-of-frame distortion.

@param tape_crease_prob float
  @range 0 0.5
  @default 0.05
  Probability of random tape crease distortion per frame.

@param blur_amount float
  @range 0 5
  @default 1
  VHS softness blur.

@param seed int
  @default 42
  Random seed for deterministic artifacts.

@state rng DeterministicRNG
  Random number generator for artifacts.

@example
  (effect vhs :tracking_error 10 :color_bleed 5)

@example
  ;; Reactive VHS glitch
  (effect vhs :tracking_error (bind onset :range [0 30]) :tape_crease_prob 0.1)
"""

import numpy as np
import cv2
from pathlib import Path
import sys

# Import DeterministicRNG from same directory
_effects_dir = Path(__file__).parent
if str(_effects_dir) not in sys.path:
    sys.path.insert(0, str(_effects_dir))
from random import DeterministicRNG


def process_frame(frame: np.ndarray, params: dict, state: dict) -> tuple:
    """
    Apply VHS effect to a video frame.

    Args:
        frame: Input frame as numpy array (H, W, 3) RGB uint8
        params: Effect parameters
        state: Persistent state dict

    Returns:
        Tuple of (processed_frame, new_state)
    """
    tracking_error = params.get("tracking_error", 5)
    color_bleed = int(params.get("color_bleed", 3))
    noise_intensity = params.get("noise_intensity", 0.2)
    chroma_shift = int(params.get("chroma_shift", 2))
    head_switching = params.get("head_switching", True)
    tape_crease_prob = params.get("tape_crease_prob", 0.05)
    blur_amount = params.get("blur_amount", 1)
    seed = int(params.get("seed", 42))

    if state is None:
        state = {}

    # Initialize RNG
    if "rng" not in state:
        state["rng"] = DeterministicRNG(seed)
    rng = state["rng"]

    h, w = frame.shape[:2]
    result = frame.astype(np.float32).copy()

    # Apply slight blur (VHS softness)
    if blur_amount > 0:
        ksize = int(blur_amount * 2) * 2 + 1
        result = cv2.GaussianBlur(result, (ksize, 1), 0)

    # Apply color bleed (horizontal color smearing)
    if color_bleed > 0:
        ksize = color_bleed * 2 + 1
        result[:, :, 0] = cv2.blur(result[:, :, 0], (ksize, 1))
        result[:, :, 2] = cv2.blur(result[:, :, 2], (ksize, 1))

    # Apply chroma shift (color channel misalignment)
    if chroma_shift > 0:
        shifted = np.zeros_like(result)
        M_r = np.float32([[1, 0, chroma_shift], [0, 1, 0]])
        M_b = np.float32([[1, 0, -chroma_shift], [0, 1, 0]])
        shifted[:, :, 0] = cv2.warpAffine(result[:, :, 0], M_r, (w, h), borderMode=cv2.BORDER_REPLICATE)
        shifted[:, :, 1] = result[:, :, 1]
        shifted[:, :, 2] = cv2.warpAffine(result[:, :, 2], M_b, (w, h), borderMode=cv2.BORDER_REPLICATE)
        result = shifted

    # Apply tracking error (horizontal line displacement)
    if tracking_error > 0:
        for y in range(h):
            sine_shift = np.sin(y * 0.05)
            rand_shift = rng.uniform(-0.3, 0.3)
            displacement = int(tracking_error * (sine_shift + rand_shift))
            if displacement != 0:
                result[y] = np.roll(result[y], displacement, axis=0)

    # Apply tape crease (random distortion bands)
    if tape_crease_prob > 0 and rng.uniform() < tape_crease_prob:
        band_start = rng.randint(0, max(1, h - 20))
        band_height = rng.randint(5, 20)
        for y in range(band_start, min(band_start + band_height, h)):
            displacement = rng.randint(-50, 50)
            result[y] = np.roll(result[y], displacement, axis=0)
            result[y] = result[y] * rng.uniform(0.5, 1.5)

    # Apply head switching noise (bottom of frame distortion)
    if head_switching:
        switch_height = rng.randint(5, 15)
        for y in range(h - switch_height, h):
            factor = (y - (h - switch_height)) / switch_height
            displacement = int(factor * 30 * rng.uniform(0.5, 1.5))
            result[y] = np.roll(result[y], displacement, axis=0)
            noise = np.array([[rng.gaussian(0, 20 * factor) for _ in range(3)] for _ in range(w)])
            result[y] = result[y] + noise

    # Apply static noise
    if noise_intensity > 0:
        noise = np.array([[[rng.gaussian(0, noise_intensity * 30) for _ in range(3)]
                          for _ in range(w)]
                         for _ in range(h)])
        result = result + noise

    return np.clip(result, 0, 255).astype(np.uint8), state