如何使用Python读取Photoshop的.act格式文件？

I spent ages searching everywhere for a way to parse Photoshop palette files (both .aco and .act formats) and couldn't find a solid, ready-to-use solution. So I rolled up my sleeves and built my own implementation—here's what I came up with, in case you're stuck too.

Parsing .act Files (The Simple One) #

The .act format is pretty straightforward—it's a binary file that holds up to 256 RGB color triplets, plus an optional transparency index. Here's a Python script to read it:

def read_act_palette(file_path):
    try:
        with open(file_path, 'rb') as f:
            # First 768 bytes = 256 RGB colors (3 bytes per color)
            rgb_bytes = f.read(768)
            palette = []
            # Iterate through each 3-byte RGB triplet
            for idx in range(0, len(rgb_bytes), 3):
                r = rgb_bytes[idx]
                g = rgb_bytes[idx + 1]
                b = rgb_bytes[idx + 2]
                palette.append((r, g, b))
            
            # Check for optional transparency index (1 extra byte)
            transparency_byte = f.read(1)
            transparency_idx = ord(transparency_byte) if transparency_byte else None
            
            return palette, transparency_idx
    except FileNotFoundError:
        print(f"Error: File {file_path} not found.")
        return None, None

How this works: #

• It reads the first 768 bytes directly into RGB values (each channel is an 8-bit integer, 0-255).
• If the file has an extra byte at the end, that's the index of the color that should be treated as transparent.

Parsing .aco Files (The More Complex Format) #

.aco files have two versions—version 1 is basic (stores RGB/CMYK/HSB values), while version 2 adds support for named colors and more color spaces. Below is a parser for version 1, which covers most standard use cases:

def read_aco_palette(file_path):
    palette = []
    try:
        with open(file_path, 'rb') as f:
            # Read version (2 bytes, big-endian) and color count (2 bytes)
            version = int.from_bytes(f.read(2), byteorder='big')
            color_count = int.from_bytes(f.read(2), byteorder='big')
            
            if version == 1:
                for _ in range(color_count):
                    # Color space identifier: 0 = RGB, 1 = HSB, 2 = CMYK, etc.
                    color_space = int.from_bytes(f.read(2), byteorder='big')
                    # Read 4 color components (each 2 bytes, big-endian)
                    comp1 = int.from_bytes(f.read(2), byteorder='big')
                    comp2 = int.from_bytes(f.read(2), byteorder='big')
                    comp3 = int.from_bytes(f.read(2), byteorder='big')
                    comp4 = int.from_bytes(f.read(2), byteorder='big')
                    
                    # Handle RGB color space (most common)
                    if color_space == 0:
                        # Convert 16-bit values (0-65535) to 8-bit (0-255)
                        r = comp1 // 256
                        g = comp2 // 256
                        b = comp3 // 256
                        palette.append((r, g, b))
                    # Add handlers for HSB/CMYK if you need them!
            # Version 2 parsing can be added to support color names, but this covers basics
    except Exception as e:
        print(f"Error reading .aco file: {str(e)}")
        return None
    return palette

Key notes for .aco: #

• The file uses big-endian byte ordering, so we specify that when converting bytes to integers.
• RGB values are stored as 16-bit integers, so we divide by 256 to get the standard 8-bit range.
• For version 2, you'd need to parse additional Unicode strings for color names—feel free to expand the code if you need that functionality!

Quick Tips for Use #

• Always add error handling (like the try-except blocks I included) to deal with corrupted files or missing paths.
• Test with palettes you export directly from Photoshop to make sure the parser behaves as expected.
• If you need to write palettes back to these formats, the logic is similar—just reverse the byte-writing steps.

内容的提问来源于stack exchange，提问作者DayDreamer