■ 🕑 1. GIF contrast adjustment
   #!/usr/bin/env python3
   # -*- coding: utf-8 -*-
   
   """
   gifedit.py - Adjust contrast of a GIF by modifying its color palette.
   
   Shouldn't touch anything but palette.
   
   Usage:./gifedit.py input.gif contrast_factor
   
   - input.gif: Path to the input GIF file.
   - contrast_factor: Floating point number where 1.0 is identity, 
                      >1.0 increases contrast, and <1.0 decreases contrast.
   
   Output: A new GIF file with the contrast-adjusted palette, named after the input file with '_contrast_{factor}.gif' appended.
   """
   
   import sys
   import os
   import struct
   
   def adjust_contrast(rgb, factor):
       """
       Apply contrast adjustment to a given RGB value.
   
       :param rgb: The RGB value to adjust (as a tuple).
       :param factor: Contrast factor (1.0 = no change, >1.0 increase, <1.0 decrease).
       :return: Adjusted RGB value.
       """
       r, g, b = rgb
       r = int(((r / 255.0 - 0.5) * factor + 0.5) * 255.0)
       g = int(((g / 255.0 - 0.5) * factor + 0.5) * 255.0)
       b = int(((b / 255.0 - 0.5) * factor + 0.5) * 255.0)
       return (max(0, min(255, r)), max(0, min(255, g)), max(0, min(255, b)))
   def main():
       if len(sys.argv)!= 3:
           print("Usage:./gifedit.py input.gif contrast_factor")
           sys.exit(1)
   
       input_file = sys.argv[1]
       try:
           contrast_factor = float(sys.argv[2])
       except ValueError:
           print("Error: Contrast factor must be a floating point number.")
           sys.exit(1)
   
       if contrast_factor <= 0:
           print("Warning: Contrast factor should be greater than zero. Proceeding with value:", contrast_factor)
   
       # Load the GIF
       try:
           with open(input_file, 'rb') as f_in:
               gif_data = f_in.read()
   
           # Verify the GIF magic bytes
           if gif_data[:6] not in [b'GIF87a', b'GIF89a']:
               print("Error: Not a GIF file.")
               sys.exit(1)
   
           # Get the original file name without extension
           filename, file_extension = os.path.splitext(input_file)
           output_file = f"{filename}_contrast_{contrast_factor:.2f}{file_extension}"
   
           # Determine the GCT size
           gct_size_byte = gif_data[10]  # 10th byte indicates GCT size (2^(N+1))
           gct_size = 2 ** ((gct_size_byte & 0x07) + 1)  # Extract the lower 3 bits
           gct_start = 13  # GCT starts after the 12th byte (header + gct_size_byte)
           gct_end = gct_start + gct_size * 3
   
           # Extract and adjust the Global Color Table
           gct = gif_data[gct_start:gct_end]
           adjusted_gct = bytearray()
           for i in range(0, len(gct), 3):
               rgb = struct.unpack('<BBB', gct[i:i+3])
               adjusted_rgb = adjust_contrast(rgb, contrast_factor)
               adjusted_gct.extend(adjusted_rgb)
   
           # Replace the original GCT with the adjusted one
           gif_data = gif_data[:gct_start] + adjusted_gct + gif_data[gct_end:]
   
           # Save the modified GIF data
           with open(output_file, 'wb') as f_out:
               f_out.write(gif_data)
           print(f"Output saved to: {output_file}")
   
       except IOError as e:
           print(f"Error opening or processing the file: {e}")
   
   if __name__ == "__main__":
       main()