Added automatic PNG resizing solver
This commit is contained in:
Philip Zimmermann
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"""Image size bruteforcer for common PNG sizes."""
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import zlib
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from pathlib import Path
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from .utils import update_data
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# Full list of expected sizes
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EXPECTED_SIZES = [
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# -------------------------
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# ICONS (Square)
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# -------------------------
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(16, 16), (20, 20), (24, 24), (28, 28),
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(32, 32), (48, 48), (64, 64), (72, 72),
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(96, 96), (128, 128), (192, 192), (256, 256),
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(384, 384), (512, 512), (768, 768), (1024, 1024),
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(1536, 1536), (2048, 2048), (4096, 4096),
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# -------------------------
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# 1:1 Square (General)
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# -------------------------
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(300, 300), (500, 500), (800, 800), (1000, 1000),
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(1500, 1500), (2000, 2000), (2500, 2500), (3000, 3000),
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# -------------------------
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# 4:3 Aspect (Classic Screens)
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# -------------------------
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(320, 240), (640, 480), (800, 600), (960, 720),
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(1024, 768), (1280, 960), (1600, 1200), (2048, 1536),
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(2560, 1920), (3200, 2400), (4096, 3072),
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# -------------------------
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# 3:2 Aspect (Photography)
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# -------------------------
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(600, 400), (900, 600), (1200, 800), (1500, 1000),
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(1800, 1200), (2400, 1600), (3000, 2000), (3600, 2400),
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(4500, 3000), (6000, 4000),
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# -------------------------
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# 16:9 Aspect (Video / Web)
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# -------------------------
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(426, 240), (640, 360), (854, 480), (960, 540),
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(1280, 720), (1366, 768), (1600, 900), (1920, 1080),
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(2560, 1440), (3200, 1800), (3440, 1935), (3840, 2160),
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(5120, 2880), (7680, 4320), (10240, 5760),
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# -------------------------
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# 16:10 Aspect (Laptops)
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# -------------------------
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(1280, 800), (1440, 900), (1680, 1050),
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(1920, 1200), (2560, 1600), (2880, 1800),
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(3840, 2400), (5120, 3200),
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# -------------------------
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# Mobile Portrait (9:16)
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# -------------------------
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(720, 1280), (1080, 1920), (1440, 2560),
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(2160, 3840), (1440, 2960), (1080, 2400),
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(1170, 2532), (1284, 2778), (1290, 2796),
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# -------------------------
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# Social Media Sizes
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# -------------------------
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# Instagram
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(1080, 1080), (1080, 1350), (1080, 1920),
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# Facebook
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(1200, 628), (1200, 1200),
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# Twitter/X
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(1200, 675), (1500, 500),
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# YouTube Thumbnails
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(1280, 720), (1920, 1080),
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# -------------------------
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# Banners / Headers
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# -------------------------
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(1600, 500), (1920, 500), (2560, 700),
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(3000, 1000), (3840, 1200),
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# -------------------------
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# Print-like Digital Sizes
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# -------------------------
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(2550, 3300), # Letter @ 300 DPI
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(2480, 3508), # A4 @ 300 DPI
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(3508, 4961), # A3 @ 300 DPI
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(4961, 7016), # A2 @ 300 DPI
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(7016, 9933), # A1 @ 300 DPI
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]
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def calc_checksum(header_chunk, width_bytes, height_bytes):
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"""
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Calculates the CRC32 of the IHDR chunk with new dimensions.
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header_chunk: The full IHDR chunk (Type + Data).
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"""
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# Reconstruct IHDR: [Type(4)] + [New Width(4)] + [New Height(4)] + [Rest of Data(5)]
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new_header = header_chunk[:4] + width_bytes + height_bytes + header_chunk[12:]
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# Calculate CRC and return as 4 bytes (Big Endian)
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return bytearray((zlib.crc32(new_header) & 0xffffffff).to_bytes(4, byteorder='big'))
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def analyze_image_resize(input_img: Path, output_dir: Path) -> None:
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"""
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Analyze an image submission using python-based resize bruteforce.
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Attempts to recover PNGs with modified resolutions but valid CRCs.
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"""
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# 1. Setup Paths
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input_img = Path(input_img)
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output_dir = Path(output_dir)
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extracted_dir = output_dir / "image_resize_output_dir"
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# 2. CREATE THE DIRECTORY (Crucial Step!)
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extracted_dir.mkdir(parents=True, exist_ok=True)
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# 3. Initialize Logs
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logs = []
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recovered_images = []
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try:
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with open(input_img, "rb") as image:
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f = image.read()
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b = bytearray(f)
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# Find IHDR start
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IHDR = b.find(b'\x49\x48\x44\x52')
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if IHDR == -1:
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logs.append("Failure: PNG header (IHDR) not found.")
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update_data(output_dir, {"image_resize": {"status": "error", "error": "PNG header not found."}})
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return
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# Calculate Chunk Length (The 4 bytes BEFORE IHDR tag)
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chunk_length = int.from_bytes((b[IHDR- 4: IHDR]), byteorder="big") + 4
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# Extract Target CRC (The 4 bytes AFTER the chunk data)
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target_crc = b[IHDR + chunk_length:IHDR + chunk_length + 4]
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# Isolate the header chunk (Type + Data)
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header_chunk = b[IHDR:IHDR + chunk_length]
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logs.append(f"Target CRC found: 0x{target_crc.hex()}")
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match_found = False
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# Brute-force Loop
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for size in EXPECTED_SIZES:
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width, height = size
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# Convert dimensions to 4-byte Big Endian arrays
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width_bytes = bytearray(width.to_bytes(4, byteorder='big'))
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height_bytes = bytearray(height.to_bytes(4, byteorder='big'))
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# Check if this size matches the file's CRC
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if target_crc == calc_checksum(header_chunk, width_bytes, height_bytes):
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match_found = True
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logs.append(f"Success: Match found! Dimensions: {width}x{height}")
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# Create Output Filename
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output_filename = f"recovered_{width}x{height}.png"
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output_path = extracted_dir / output_filename
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# Splicing: [Start...IHDR+4] + [W] + [H] + [IHDR+12...End]
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full_png_data = b[:IHDR+4] + width_bytes + height_bytes + b[IHDR+12:]
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# Write the recovered file to disk
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with open(output_path, "wb") as out_f:
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out_f.write(full_png_data)
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recovered_images.append(output_filename)
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break # Stop looking after finding the match
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if not match_found:
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logs.append("Failure: No matching dimensions found.")
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# 4. Final Data Update
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output_data = {
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"image_resize": { # Key name must match your module name in AperiSolve
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"status": "ok",
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"output": logs,
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"images": recovered_images, # Tells frontend to display the image
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}
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}
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update_data(output_dir, output_data)
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except Exception as e:
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update_data(output_dir, {"image_resize": {"status": "error", "error": str(e)}})
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return None
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