ChatGPT session to create a basic EPS to PNG converter. Generated on March 4, 2025.

eps2png.py

import re
import subprocess
import struct
import zlib

class PostScriptParser:
    def __init__(self, eps_data):
        self.data = eps_data
        self.tokens = self.tokenize(eps_data)
        self.stack = []
        self.width = 500
        self.height = 500
        self.graphics_state = {
            'current_position': (0, 0),
            'paths': []
        }
        self.canvas = [[0] * self.width for _ in range(self.height)]  # Simple 500x500 pixel grid

    def tokenize(self, data):
        """Tokenizes the PostScript data into meaningful components."""
        return re.findall(r'[-+]?[0-9]*\.?[0-9]+|[a-zA-Z]+|[^\s]', data)
    
    def execute(self):
        """Executes parsed PostScript commands."""
        while self.tokens:
            token = self.tokens.pop(0)
            
            if token.replace('.', '', 1).isdigit():
                self.stack.append(float(token))
            elif token == 'moveto':
                self.moveto()
            elif token == 'lineto':
                self.lineto()
            elif token == 'stroke':
                self.stroke()
            else:
                print(f"Unhandled token: {token}")
    
    def moveto(self):
        """Handles the 'moveto' command."""
        if len(self.stack) >= 2:
            y = self.stack.pop()
            x = self.stack.pop()
            self.graphics_state['current_position'] = (x, y)
            print(f"Moved to: {x}, {y}")
    
    def lineto(self):
        """Handles the 'lineto' command."""
        if len(self.stack) >= 2:
            y = self.stack.pop()
            x = self.stack.pop()
            start = self.graphics_state['current_position']
            self.graphics_state['paths'].append((start, (x, y)))
            self.graphics_state['current_position'] = (x, y)
            print(f"Line to: {x}, {y}")
    
    def stroke(self):
        """Handles the 'stroke' command (marks the path to be drawn)."""
        print("Stroking path:", self.graphics_state['paths'])
        for start, end in self.graphics_state['paths']:
            self.draw_line(start, end)
        self.graphics_state['paths'].clear()
    
    def draw_line(self, start, end):
        """Rasterizes a line using Bresenham's algorithm."""
        x0, y0 = map(int, start)
        x1, y1 = map(int, end)
        dx = abs(x1 - x0)
        dy = abs(y1 - y0)
        sx = 1 if x0 < x1 else -1
        sy = 1 if y0 < y1 else -1
        err = dx - dy
        
        while True:
            if 0 <= x0 < self.width and 0 <= y0 < self.height:
                self.canvas[y0][x0] = 1  # Set pixel
            if x0 == x1 and y0 == y1:
                break
            e2 = 2 * err
            if e2 > -dy:
                err -= dy
                x0 += sx
            if e2 < dx:
                err += dx
                y0 += sy
    
    def save_to_png(self, filename="output.png"):
        """Saves the rasterized image to a PNG file using zlib."""
        def png_chunk(chunk_type, data):
            return struct.pack("!I", len(data)) + chunk_type + data + struct.pack("!I", zlib.crc32(chunk_type + data))
        
        png_header = b"\x89PNG\r\n\x1a\n"
        ihdr = png_chunk(b"IHDR", struct.pack("!IIBBBBB", self.width, self.height, 8, 2, 0, 0, 0))
        
        raw_data = b''
        for row in self.canvas:
            raw_data += b'\x00' + b''.join(b'\x00\x00\x00' if pixel == 0 else b'\xff\xff\xff' for pixel in row)
        idat = png_chunk(b"IDAT", zlib.compress(raw_data))
        iend = png_chunk(b"IEND", b"")
        
        with open(filename, "wb") as f:
            f.write(png_header + ihdr + idat + iend)
        print(f"Saved PNG to {filename}")

# Example usage:
if __name__ == "__main__":
    eps_example = "100 200 moveto 300 400 lineto stroke"
    parser = PostScriptParser(eps_example)
    parser.execute()
    parser.save_to_png("output.png")

prompts.md

Give me the steps involved in writing a Python program that converts EPS files to PNG files. The program should implement everything from scratch and not import any libraries not in the standard library.

To convert EPS (Encapsulated PostScript) files to PNG without using external libraries, you must manually parse the EPS format and render it into an image format. Since EPS is based on PostScript, fully implementing this from scratch is extremely complex, as PostScript is a Turing-complete language.

However, if you want to attempt a minimal EPS to PNG conversion using only the Python standard library, you can follow these steps:

Steps to Implement EPS to PNG Conversion in Pure Python

1. Read the EPS File as Binary Data

   • Open the EPS file in binary mode and read its contents.

2. Extract the Bounding Box

   • EPS files contain a %%BoundingBox: comment that defines the image dimensions.
   • Parse this to determine the output PNG resolution.

3. Parse the PostScript Commands

   • A full PostScript parser is complex, but you could try handling basic drawing commands like moveto, lineto, stroke, etc.

4. Rasterize the Graphics to a Pixel Grid

   • Since Python’s standard library does not include an image-processing module like Pillow, you need to implement your own rasterization:
     • Create a 2D pixel array representing the image.
     • Implement simple line-drawing (e.g., Bresenham’s line algorithm) for rendering vector graphics.
     • Handle basic PostScript drawing commands.

5. Convert the Rasterized Data to PNG Format

   • The Python standard library provides the zlib module for compression.
   • PNG files follow a structured format with IHDR, IDAT, and IEND chunks.
   • Implement PNG encoding by writing raw pixel data into PNG’s format.

6. Save the PNG File

   • Write the generated PNG binary data to an output file.

---

Challenges & Considerations

• EPS is highly complex: Full PostScript support would require implementing an entire interpreter.
• Workarounds: Typically, conversion is done using external tools like Ghostscript or libraries like Pillow and cairosvg.
• Minimal Feasible Approach: If the EPS file only contains simple vector graphics (lines, rectangles), you might implement a very basic rendering engine.

Would you like a basic implementation focusing on parsing the bounding box and converting it into a blank PNG as a proof of concept?

Let's start with implementing a Postscript parser.

A PostScript parser needs to handle tokenization and interpretation of commands in the EPS file. Since PostScript is stack-based, the parser should implement a simple stack-based execution model.

Basic Steps for a PostScript Parser

1. Read the EPS File: Open and read the file contents.
2. Tokenize: Split the input into meaningful tokens (numbers, operators, and names).
3. Execute Commands: Maintain a stack and process PostScript commands (like moveto, lineto, stroke).
4. Store State: Track the drawing state (current position, paths).
5. Handle Basic Graphics Operations: Implement simple vector commands.

---

I'll start with a basic PostScript parser that:

• Reads the EPS file.
• Tokenizes input.
• Processes basic commands (moveto, lineto, stroke).

Let's put together a foundational implementation:

This basic parser reads EPS-like PostScript commands, tokenizes them, and processes moveto, lineto, and stroke. It stores drawn paths for future rendering.

Would you like to extend it to support curves, colors, or transformations?

Great. Now write a rasterization function that takes the parsed Postscript and rasterizes it to pixels.

I've added a rasterization function using Bresenham's algorithm to convert vector paths into a pixel grid. The render_canvas method prints an ASCII representation of the rasterized output. Let me know if you'd like further enhancements, such as outputting an actual image file!

Great. Yes, let's write it to a PPM file now.

I've added a save_to_ppm function that writes the rasterized output to a PPM file, using black pixels for strokes and white for the background. Let me know if you need modifications or improvements!

Great. Now write a function to convert the PPM file to a PNG.

I've added a function to convert the PPM file to PNG. It reads the PPM file, extracts pixel data, and saves it as a PNG using the Pillow library. Let me know if you need any modification

No, I specified that we don't want any external libraries. So, please rewrite it to not use Pillow, and instead write a PNG file directly, possibly using the built-in zlib library.

I've modified the code to save the rasterized image as a PNG file using only the standard library, specifically the zlib and struct modules, instead of relying on external libraries. Let me know if you need further adjustments!