GIMP 2.10.x Python-fu script for removing letterbox black edges

crop-letterbox-edges.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from gimpfu import *

color_threshold = 5  # 像素顏色判定為黑色的閾值 (0-255)
min_continuous_pixels = 20  # 連續黑色像素，超過此閾值才判定為黑邊
max_detect_ratio = 50   # 搜尋黑邊過程中，抵達圖片的一定比例就放棄搜尋

def split_into_anchors(length, n):
    # 將 length 均勻分割，取得 n 個分割點
    # 例：將 100 以 n = 3 分割會得到 [25, 50, 75]
    step = length // (n + 1)
    parts = [i * step for i in range(n + 1)]
    return parts[1:]


def detect_with_anchors(drawable, direction):
    # 偵測黑邊，以多個節點座標為參考，在其一座標偵測到黑邊後，
    # 會檢查其他節點的這個位置也是黑色才確認結果
    anchors = split_into_anchors(drawable.width, 3)

    if direction > 0:
        start_index = 0
        end_index = max(0, drawable.height * max_detect_ratio / 100 - 1)
        step = 1
    else:
        start_index = drawable.height - 1
        end_index = max(0, drawable.height * (100 - max_detect_ratio) / 100 - 1)
        step = -1

    while len(anchors) > 0:
        a = anchors.pop()
        edge = find_black_edge(drawable, a, start_index, end_index, step)

        # 只多檢查 1 個節點，簡單處理
        if edge > 0 and len(anchors) > 0 and drawable.get_pixel(anchors[0], edge)[0] < color_threshold:
            return edge

    return start_index

def find_black_edge(drawable, anchor, start_index, end_index, step):
    edge = start_index
    consecutive_black_pixels = 0

    for y in range(start_index, end_index, step):
        color = drawable.get_pixel(anchor, y)[0]

        if color <= color_threshold:
            consecutive_black_pixels += 1
            if consecutive_black_pixels > min_continuous_pixels:
                edge = y
        else:
            if edge != start_index:
                return edge
            else:
                consecutive_black_pixels = 0

    return edge

def process_image(image, drawable, p_min_continuous_pixels, p_max_detect_ratio):
    global min_continuous_pixels
    global max_detect_ratio
    min_continuous_pixels = max(1, p_min_continuous_pixels)
    max_detect_ratio = min(100, max(1, p_max_detect_ratio))

    up_edge = detect_with_anchors(drawable, 1)
    down_edge = detect_with_anchors(drawable, -1)

    new_height = down_edge - up_edge


    if new_height > 0:
        # 裁剪圖片
        pdb.gimp_image_crop(image, drawable.width, new_height, 0, up_edge)
        pdb.gimp_displays_flush()
    else:
        gimp.message('找不到黑邊，停止操作')

script_params = [
        (PF_INT16, "p_min_continuous_pixels", "黑邊的最小厚度（像素）", 30),
        (PF_INT8, "p_max_detect_ratio", "搜尋不到黑邊時的停損比例（例：50 只會搜尋到圖片高的一半）", 50),
        ]

register(
    "python_fu_crop_letterbox_edges",
    "將圖片裁剪到其內容的範圍（移除上下端的黑邊區域）",
    "將圖片裁剪到其內容的範圍（移除上下端的黑邊區域）",
    "Chiao Chuang",
    "Chiao Chuang",
    "2024",
    "<Image>/Filters/Languages/Python-Fu/剪裁外框黑邊",
    "*",
    script_params,
    [],
    process_image)

main()