pi-dashboard/pi/image_handler.py

"""Status image functions — loading, alpha compositing, and WS transmission."""

import json
import logging
from pathlib import Path

from PIL import Image

log = logging.getLogger(__name__)

IMG_DIR = Path(__file__).parent / "assets" / "img"
STATUS_IMG_SIZE = 200
MONOCHROME_THRESHOLD = 180


def load_status_image(path: Path) -> bytes:
    """Load a PNG, convert to 1-bit 200x200 monochrome bitmap (MSB-first, black=1).

    Transparent pixels are composited onto white so they don't render as black.
    """
    img = Image.open(path)

    # Composite transparent pixels onto white background
    if img.mode in ("RGBA", "LA", "PA"):
        bg = Image.new("RGBA", img.size, (255, 255, 255, 255))
        bg.paste(img, mask=img.split()[-1])
        img = bg

    img = img.convert("L")

    # Resize to fit within 120x120, preserving aspect ratio
    img.thumbnail((STATUS_IMG_SIZE, STATUS_IMG_SIZE), Image.LANCZOS)

    # Paste centered onto white canvas
    canvas = Image.new("L", (STATUS_IMG_SIZE, STATUS_IMG_SIZE), 255)
    x_off = (STATUS_IMG_SIZE - img.width) // 2
    y_off = (STATUS_IMG_SIZE - img.height) // 2
    canvas.paste(img, (x_off, y_off))

    # Threshold to 1-bit: black (< MONOCHROME_THRESHOLD) -> 1, white -> 0
    bw = canvas.point(lambda p: 1 if p < MONOCHROME_THRESHOLD else 0, "1")
    raw = bw.tobytes()
    log.info("Status image loaded: %s -> %d bytes", path.name, len(raw))
    return raw


async def send_status_image(ws, img_bytes: bytes):
    """Send a status image over the WebSocket (text header + binary payload)."""
    header = json.dumps({"type": "status_image", "width": STATUS_IMG_SIZE, "height": STATUS_IMG_SIZE})
    await ws.send(header)
    await ws.send(img_bytes)
    log.info("Sent status image (%d bytes)", len(img_bytes))