| """Image preprocessing, identical to the original application. |
| |
| ToTensor -> zero-pad to square (centred) -> resize to 448 x 448, bilinear, |
| no antialiasing, no mean/std normalisation. |
| |
| ``antialias=False`` reproduces tensor resizing in torchvision 0.13 |
| (PyTorch 1.12.1, the version bundled in toolv9). Newer torchvision versions |
| default to ``antialias=True``, which changes the input noticeably. |
| """ |
| from __future__ import annotations |
|
|
| import torchvision.transforms.functional as F |
| from PIL import Image |
| from torchvision import transforms |
|
|
| |
| ACCEPTED_FORMATS = {"JPEG", "PNG", "TIFF", "MPO"} |
|
|
|
|
| def square_pad(t): |
| """Replica of the app's SquarePad, including its rounding of odd differences.""" |
| h, w = t.size()[-2:] |
| m = max(h, w) |
| top = int((m - h) / 2) |
| left = int((m - w) / 2) |
| |
| return F.pad(t, (left, top, left, top), 0, "constant") |
|
|
|
|
| TRANSFORM = transforms.Compose([ |
| transforms.ToTensor(), |
| square_pad, |
| transforms.Resize((448, 448), antialias=False), |
| ]) |
|
|
|
|
| def app_would_read(path: str) -> bool: |
| """Replicates the app's file filter: Python 3.8 ``imghdr.what(path) in ('jpeg', 'png', 'tiff')``. |
| |
| Python 3.8 imghdr recognises a JPEG only if bytes 6-10 are 'JFIF' or 'Exif', |
| so JPEGs without those headers were silently ignored by the desktop app. |
| """ |
| try: |
| with open(path, "rb") as f: |
| h = f.read(32) |
| except OSError: |
| return False |
| if h[6:10] in (b"JFIF", b"Exif"): |
| return True |
| if h.startswith(b"\211PNG\r\n\032\n"): |
| return True |
| if h[:6] in (b"GIF87a", b"GIF89a"): |
| return False |
| return h[:2] in (b"MM", b"II") |
|
|
|
|
| def open_image(path: str): |
| """Open an image; return None if it is not a readable JPEG/PNG/TIFF.""" |
| try: |
| img = Image.open(path) |
| if img.format not in ACCEPTED_FORMATS: |
| return None |
| return img.convert("RGB") |
| except Exception: |
| return None |
|
|
|
|
| def to_tensor(img: Image.Image): |
| return TRANSFORM(img.convert("RGB")).unsqueeze(0) |
|
|
