judge2020 · March 29, 2025 13:21 · Mar 29, 2025 · Mar 28, 2025
diff --git a/_README.md b/_README.md
@@ -0,0 +1,12 @@
+## Trim transparency from bounds of a gif
+
+Sometimes you have a gif that has a transparent pixel border. This is inconvenient when you don't want this for chat-app emojis or stickers.
+
+Courtest of chatgpt here's a script that takes in a gif via python input and outputs the trimmed gif.
+
+## prerequisites
+
+- ffmpeg
+- gifski (no video mode needed)
+- python3
+- numpy
diff --git a/crop_and_create_gif.py b/crop_and_create_gif.py
@@ -0,0 +1,110 @@
+#!/usr/bin/env python3
+import os
+import sys
+import glob
+import subprocess
+import numpy as np
+from PIL import Image
+import time
+import re
+
+def get_nontransparent_bbox(im):
+    """
+    Returns the bounding box (left, top, right, bottom) of the non-transparent region.
+    If the image is completely transparent, returns the full image box.
+    """
+    im = im.convert("RGBA")
+    arr = np.array(im)
+    # Mask: True where alpha channel is non-zero (non-transparent)
+    mask = arr[..., 3] != 0
+    coords = np.argwhere(mask)
+    if coords.size == 0:
+        return (0, 0, im.width, im.height)
+    y0, x0 = coords.min(axis=0)
+    y1, x1 = coords.max(axis=0)
+    # PIL crop: right and bottom are non-inclusive, so add 1
+    return (x0, y0, x1 + 1, y1 + 1)
+
+def safe_directory_name(name):
+    """
+    Creates a directory-safe string by replacing non-alphanumeric characters with underscores.
+    """
+    return re.sub(r'[^A-Za-z0-9_\-]', '_', name)
+
+def main():
+    # Prompt user for the input GIF file
+    gif_file = input("Enter the name of the GIF file (in current directory): ").strip()
+    if not os.path.isfile(gif_file):
+        print(f"Error: File '{gif_file}' does not exist.")
+        sys.exit(1)
+
+    # Create a unique directory name for extracted frames
+    base_name = os.path.splitext(os.path.basename(gif_file))[0]
+    safe_name = safe_directory_name(base_name)
+    frames_dir = safe_name + "_frames"
+    if os.path.exists(frames_dir):
+        # Append a timestamp to ensure uniqueness
+        frames_dir += "_" + str(int(time.time()))
+    os.makedirs(frames_dir, exist_ok=True)
+    print(f"Extracting frames to directory: {frames_dir}")
+
+    # Extract frames using ffmpeg
+    ffmpeg_cmd = f'ffmpeg -i "{gif_file}" "{frames_dir}/%04d.png"'
+    print(f"Running: {ffmpeg_cmd}")
+    subprocess.run(ffmpeg_cmd, shell=True, check=True)
+
+    # List extracted PNG files (sorted)
+    png_files = sorted(glob.glob(os.path.join(frames_dir, "*.png")))
+    if not png_files:
+        print("Error: No PNG frames found after extraction.")
+        sys.exit(1)
+
+    # Compute the union bounding box of non-transparent areas from all frames
+    global_left, global_top = float('inf'), float('inf')
+    global_right, global_bottom = 0, 0
+
+    for png in png_files:
+        im = Image.open(png)
+        left, top, right, bottom = get_nontransparent_bbox(im)
+        global_left = min(global_left, left)
+        global_top = min(global_top, top)
+        global_right = max(global_right, right)
+        global_bottom = max(global_bottom, bottom)
+
+    print(f"Global bounding box: left={global_left}, top={global_top}, right={global_right}, bottom={global_bottom}")
+
+    # Create a directory for cropped images
+    cropped_dir = "cropped"
+    if os.path.exists(cropped_dir):
+        cropped_dir = safe_name + "_cropped"
+        if os.path.exists(cropped_dir):
+            cropped_dir += "_" + str(int(time.time()))
+    os.makedirs(cropped_dir, exist_ok=True)
+
+    # Crop each PNG to the union bounding box and save into the cropped directory
+    for png in png_files:
+        im = Image.open(png)
+        cropped = im.crop((global_left, global_top, global_right, global_bottom))
+        filename = os.path.basename(png)
+        cropped.save(os.path.join(cropped_dir, filename))
+        print(f"Cropped and saved {filename}")
+
+    # Extract the frame rate from the original GIF using ffprobe
+    ffprobe_cmd = (
+        f'ffprobe -v error -select_streams v:0 -show_entries stream=r_frame_rate '
+        f'-of default=noprint_wrappers=1:nokey=1 "{gif_file}"'
+    )
+    fps_output = subprocess.check_output(ffprobe_cmd, shell=True).decode().strip()
+    num, denom = fps_output.split('/')
+    fps = float(num) / float(denom)
+    print(f"Extracted frame rate: {fps} fps")
+
+    # Use gifski to create the output GIF from the cropped images
+    output_gif = safe_name + "_output.gif"
+    gifski_cmd = f'gifski --fps {fps} -o "{output_gif}" {cropped_dir}/*.png'
+    print(f"Running: {gifski_cmd}")
+    subprocess.run(gifski_cmd, shell=True, check=True)
+    print(f"Created output GIF: {output_gif}")
+
+if __name__ == "__main__":
+    main()
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