Files
breakpilot-lehrer/klausur-service/backend/cv_vocab_pipeline.py
Benjamin Admin 09b820efbe refactor(dewarp): replace displacement map with affine shear correction
The old displacement-map approach shifted entire rows by a parabolic
profile, creating a circle/barrel distortion. The actual problem is
a linear vertical shear: after deskew aligns horizontal lines, the
vertical column edges are still tilted by ~0.5°.

New approach:
- Detect shear angle from strongest vertical edge slope (not curvature)
- Apply cv2.warpAffine shear to straighten vertical features
- Manual slider: -2.0° to +2.0° in 0.05° steps
- Slider initializes to auto-detected shear angle
- Ground truth question: "Spalten vertikal ausgerichtet?"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-02-26 18:23:04 +01:00

1313 lines
44 KiB
Python

"""
CV-based Document Reconstruction Pipeline for Vocabulary Extraction.
Uses classical Computer Vision techniques for high-quality OCR:
- High-resolution PDF rendering (432 DPI)
- Deskew (rotation correction via Hough Lines)
- Dewarp (book curvature correction) — pass-through initially
- Dual image preparation (binarized for OCR, CLAHE for layout)
- Projection-profile layout analysis (column/row detection)
- Multi-pass Tesseract OCR with region-specific PSM settings
- Y-coordinate line alignment for vocabulary matching
- Optional LLM post-correction for low-confidence regions
Lizenz: Apache 2.0 (kommerziell nutzbar)
DATENSCHUTZ: Alle Verarbeitung erfolgt lokal.
"""
import io
import logging
import time
from dataclasses import dataclass, field
from typing import List, Dict, Any, Optional, Tuple
import numpy as np
logger = logging.getLogger(__name__)
# --- Availability Guards ---
try:
import cv2
CV2_AVAILABLE = True
except ImportError:
cv2 = None
CV2_AVAILABLE = False
logger.warning("OpenCV not available — CV pipeline disabled")
try:
import pytesseract
from PIL import Image
TESSERACT_AVAILABLE = True
except ImportError:
pytesseract = None
Image = None
TESSERACT_AVAILABLE = False
logger.warning("pytesseract/Pillow not available — CV pipeline disabled")
CV_PIPELINE_AVAILABLE = CV2_AVAILABLE and TESSERACT_AVAILABLE
# --- Data Classes ---
@dataclass
class PageRegion:
"""A detected region on the page."""
type: str # 'column_en', 'column_de', 'column_example', 'header', 'footer'
x: int
y: int
width: int
height: int
@dataclass
class VocabRow:
"""A single vocabulary entry assembled from multi-column OCR."""
english: str = ""
german: str = ""
example: str = ""
confidence: float = 0.0
y_position: int = 0
@dataclass
class PipelineResult:
"""Complete result of the CV pipeline."""
vocabulary: List[Dict[str, Any]] = field(default_factory=list)
word_count: int = 0
columns_detected: int = 0
duration_seconds: float = 0.0
stages: Dict[str, float] = field(default_factory=dict)
error: Optional[str] = None
image_width: int = 0
image_height: int = 0
# =============================================================================
# Stage 1: High-Resolution PDF Rendering
# =============================================================================
def render_pdf_high_res(pdf_data: bytes, page_number: int = 0, zoom: float = 3.0) -> np.ndarray:
"""Render a PDF page to a high-resolution numpy array (BGR).
Args:
pdf_data: Raw PDF bytes.
page_number: 0-indexed page number.
zoom: Zoom factor (3.0 = 432 DPI).
Returns:
numpy array in BGR format.
"""
import fitz # PyMuPDF
pdf_doc = fitz.open(stream=pdf_data, filetype="pdf")
if page_number >= pdf_doc.page_count:
raise ValueError(f"Page {page_number} does not exist (PDF has {pdf_doc.page_count} pages)")
page = pdf_doc[page_number]
mat = fitz.Matrix(zoom, zoom)
pix = page.get_pixmap(matrix=mat)
# Convert to numpy BGR
img_data = np.frombuffer(pix.samples, dtype=np.uint8).reshape(pix.h, pix.w, pix.n)
if pix.n == 4: # RGBA
img_bgr = cv2.cvtColor(img_data, cv2.COLOR_RGBA2BGR)
elif pix.n == 3: # RGB
img_bgr = cv2.cvtColor(img_data, cv2.COLOR_RGB2BGR)
else: # Grayscale
img_bgr = cv2.cvtColor(img_data, cv2.COLOR_GRAY2BGR)
pdf_doc.close()
return img_bgr
def render_image_high_res(image_data: bytes) -> np.ndarray:
"""Load an image (PNG/JPEG) into a numpy array (BGR).
Args:
image_data: Raw image bytes.
Returns:
numpy array in BGR format.
"""
img_array = np.frombuffer(image_data, dtype=np.uint8)
img_bgr = cv2.imdecode(img_array, cv2.IMREAD_COLOR)
if img_bgr is None:
raise ValueError("Could not decode image data")
return img_bgr
# =============================================================================
# Stage 2: Deskew (Rotation Correction)
# =============================================================================
def deskew_image(img: np.ndarray) -> Tuple[np.ndarray, float]:
"""Correct rotation using Hough Line detection.
Args:
img: BGR image.
Returns:
Tuple of (corrected image, detected angle in degrees).
"""
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
# Binarize for line detection
_, binary = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY_INV + cv2.THRESH_OTSU)
# Detect lines
lines = cv2.HoughLinesP(binary, 1, np.pi / 180, threshold=100,
minLineLength=img.shape[1] // 4, maxLineGap=20)
if lines is None or len(lines) < 3:
return img, 0.0
# Compute angles of near-horizontal lines
angles = []
for line in lines:
x1, y1, x2, y2 = line[0]
angle = np.degrees(np.arctan2(y2 - y1, x2 - x1))
if abs(angle) < 15: # Only near-horizontal
angles.append(angle)
if not angles:
return img, 0.0
median_angle = float(np.median(angles))
# Limit correction to ±5°
if abs(median_angle) > 5.0:
median_angle = 5.0 * np.sign(median_angle)
if abs(median_angle) < 0.1:
return img, 0.0
# Rotate
h, w = img.shape[:2]
center = (w // 2, h // 2)
M = cv2.getRotationMatrix2D(center, median_angle, 1.0)
corrected = cv2.warpAffine(img, M, (w, h),
flags=cv2.INTER_LINEAR,
borderMode=cv2.BORDER_REPLICATE)
logger.info(f"Deskew: corrected {median_angle:.2f}° rotation")
return corrected, median_angle
def deskew_image_by_word_alignment(
image_data: bytes,
lang: str = "eng+deu",
downscale_factor: float = 0.5,
) -> Tuple[bytes, float]:
"""Correct rotation by fitting a line through left-most word starts per text line.
More robust than Hough-based deskew for vocabulary worksheets where text lines
have consistent left-alignment. Runs a quick Tesseract pass on a downscaled
copy to find word positions, computes the dominant left-edge column, fits a
line through those points and rotates the full-resolution image.
Args:
image_data: Raw image bytes (PNG/JPEG).
lang: Tesseract language string for the quick pass.
downscale_factor: Shrink factor for the quick Tesseract pass (0.5 = 50%).
Returns:
Tuple of (rotated image as PNG bytes, detected angle in degrees).
"""
if not CV2_AVAILABLE or not TESSERACT_AVAILABLE:
return image_data, 0.0
# 1. Decode image
img_array = np.frombuffer(image_data, dtype=np.uint8)
img = cv2.imdecode(img_array, cv2.IMREAD_COLOR)
if img is None:
logger.warning("deskew_by_word_alignment: could not decode image")
return image_data, 0.0
orig_h, orig_w = img.shape[:2]
# 2. Downscale for fast Tesseract pass
small_w = int(orig_w * downscale_factor)
small_h = int(orig_h * downscale_factor)
small = cv2.resize(img, (small_w, small_h), interpolation=cv2.INTER_AREA)
# 3. Quick Tesseract — word-level positions
pil_small = Image.fromarray(cv2.cvtColor(small, cv2.COLOR_BGR2RGB))
try:
data = pytesseract.image_to_data(
pil_small, lang=lang, config="--psm 6 --oem 3",
output_type=pytesseract.Output.DICT,
)
except Exception as e:
logger.warning(f"deskew_by_word_alignment: Tesseract failed: {e}")
return image_data, 0.0
# 4. Per text-line, find the left-most word start
# Group by (block_num, par_num, line_num)
from collections import defaultdict
line_groups: Dict[tuple, list] = defaultdict(list)
for i in range(len(data["text"])):
text = (data["text"][i] or "").strip()
conf = int(data["conf"][i])
if not text or conf < 20:
continue
key = (data["block_num"][i], data["par_num"][i], data["line_num"][i])
line_groups[key].append(i)
if len(line_groups) < 5:
logger.info(f"deskew_by_word_alignment: only {len(line_groups)} lines, skipping")
return image_data, 0.0
# For each line, pick the word with smallest 'left' → compute (left_x, center_y)
# Scale back to original resolution
scale = 1.0 / downscale_factor
points = [] # list of (x, y) in original-image coords
for key, indices in line_groups.items():
best_idx = min(indices, key=lambda i: data["left"][i])
lx = data["left"][best_idx] * scale
top = data["top"][best_idx] * scale
h = data["height"][best_idx] * scale
cy = top + h / 2.0
points.append((lx, cy))
# 5. Find dominant left-edge column + compute angle
xs = np.array([p[0] for p in points])
ys = np.array([p[1] for p in points])
median_x = float(np.median(xs))
tolerance = orig_w * 0.03 # 3% of image width
mask = np.abs(xs - median_x) <= tolerance
filtered_xs = xs[mask]
filtered_ys = ys[mask]
if len(filtered_xs) < 5:
logger.info(f"deskew_by_word_alignment: only {len(filtered_xs)} aligned points after filter, skipping")
return image_data, 0.0
# polyfit: x = a*y + b → a = dx/dy → angle = arctan(a)
coeffs = np.polyfit(filtered_ys, filtered_xs, 1)
slope = coeffs[0] # dx/dy
angle_rad = np.arctan(slope)
angle_deg = float(np.degrees(angle_rad))
# Clamp to ±5°
angle_deg = max(-5.0, min(5.0, angle_deg))
logger.info(f"deskew_by_word_alignment: detected {angle_deg:.2f}° from {len(filtered_xs)} points "
f"(total lines: {len(line_groups)})")
if abs(angle_deg) < 0.05:
return image_data, 0.0
# 6. Rotate full-res image
center = (orig_w // 2, orig_h // 2)
M = cv2.getRotationMatrix2D(center, angle_deg, 1.0)
rotated = cv2.warpAffine(img, M, (orig_w, orig_h),
flags=cv2.INTER_LINEAR,
borderMode=cv2.BORDER_REPLICATE)
# Encode back to PNG
success, png_buf = cv2.imencode(".png", rotated)
if not success:
logger.warning("deskew_by_word_alignment: PNG encoding failed")
return image_data, 0.0
return png_buf.tobytes(), angle_deg
# =============================================================================
# Stage 3: Dewarp (Book Curvature Correction)
# =============================================================================
def _detect_shear_angle(img: np.ndarray) -> Dict[str, Any]:
"""Detect the vertical shear angle of the page.
After deskew (horizontal lines aligned), vertical features like column
edges may still be tilted. This measures that tilt by tracking the
strongest vertical edge across horizontal strips.
The result is a shear angle in degrees: the angular difference between
true vertical and the detected column edge.
Returns:
Dict with keys: method, shear_degrees, confidence.
"""
h, w = img.shape[:2]
result = {"method": "vertical_edge", "shear_degrees": 0.0, "confidence": 0.0}
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
# Vertical Sobel to find vertical edges
sobel_x = cv2.Sobel(gray, cv2.CV_64F, 1, 0, ksize=3)
abs_sobel = np.abs(sobel_x).astype(np.uint8)
# Binarize with Otsu
_, binary = cv2.threshold(abs_sobel, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)
num_strips = 20
strip_h = h // num_strips
edge_positions = [] # (y_center, x_position)
for i in range(num_strips):
y_start = i * strip_h
y_end = min((i + 1) * strip_h, h)
strip = binary[y_start:y_end, :]
# Project vertically (sum along y-axis)
projection = np.sum(strip, axis=0).astype(np.float64)
if projection.max() == 0:
continue
# Find the strongest vertical edge in left 40% of image
search_w = int(w * 0.4)
left_proj = projection[:search_w]
if left_proj.max() == 0:
continue
# Smooth and find peak
kernel_size = max(3, w // 100)
if kernel_size % 2 == 0:
kernel_size += 1
smoothed = cv2.GaussianBlur(left_proj.reshape(1, -1), (kernel_size, 1), 0).flatten()
x_pos = float(np.argmax(smoothed))
y_center = (y_start + y_end) / 2.0
edge_positions.append((y_center, x_pos))
if len(edge_positions) < 8:
return result
ys = np.array([p[0] for p in edge_positions])
xs = np.array([p[1] for p in edge_positions])
# Remove outliers (> 2 std from median)
median_x = np.median(xs)
std_x = max(np.std(xs), 1.0)
mask = np.abs(xs - median_x) < 2 * std_x
ys = ys[mask]
xs = xs[mask]
if len(ys) < 6:
return result
# Fit straight line: x = slope * y + intercept
# The slope tells us the tilt of the vertical edge
straight_coeffs = np.polyfit(ys, xs, 1)
slope = straight_coeffs[0] # dx/dy in pixels
fitted = np.polyval(straight_coeffs, ys)
residuals = xs - fitted
rmse = float(np.sqrt(np.mean(residuals ** 2)))
# Convert slope to angle: arctan(dx/dy) in degrees
import math
shear_degrees = math.degrees(math.atan(slope))
confidence = min(1.0, len(ys) / 15.0) * max(0.5, 1.0 - rmse / 5.0)
result["shear_degrees"] = round(shear_degrees, 3)
result["confidence"] = round(float(confidence), 2)
return result
def _apply_shear(img: np.ndarray, shear_degrees: float) -> np.ndarray:
"""Apply a vertical shear correction to an image.
Shifts each row horizontally proportional to its distance from the
vertical center. This corrects the tilt of vertical features (columns)
without affecting horizontal alignment (text lines).
Args:
img: BGR image.
shear_degrees: Shear angle in degrees. Positive = shift top-right/bottom-left.
Returns:
Corrected image.
"""
import math
h, w = img.shape[:2]
shear_tan = math.tan(math.radians(shear_degrees))
# Affine matrix: shift x by shear_tan * (y - h/2)
# [1 shear_tan -h/2*shear_tan]
# [0 1 0 ]
M = np.float32([
[1, shear_tan, -h / 2.0 * shear_tan],
[0, 1, 0],
])
corrected = cv2.warpAffine(img, M, (w, h),
flags=cv2.INTER_LINEAR,
borderMode=cv2.BORDER_REPLICATE)
return corrected
def dewarp_image(img: np.ndarray) -> Tuple[np.ndarray, Dict[str, Any]]:
"""Correct vertical shear after deskew.
After deskew aligns horizontal text lines, vertical features (column
edges) may still be tilted. This detects the tilt angle of the strongest
vertical edge and applies an affine shear correction.
Args:
img: BGR image (already deskewed).
Returns:
Tuple of (corrected_image, dewarp_info).
dewarp_info keys: method, shear_degrees, confidence.
"""
no_correction = {
"method": "none",
"shear_degrees": 0.0,
"confidence": 0.0,
}
if not CV2_AVAILABLE:
return img, no_correction
t0 = time.time()
detection = _detect_shear_angle(img)
duration = time.time() - t0
shear_deg = detection["shear_degrees"]
confidence = detection["confidence"]
logger.info(f"dewarp: detected shear={shear_deg:.3f}° "
f"conf={confidence:.2f} ({duration:.2f}s)")
# Only correct if shear is significant (> 0.05°)
if abs(shear_deg) < 0.05 or confidence < 0.3:
return img, no_correction
# Apply correction (negate the detected shear to straighten)
corrected = _apply_shear(img, -shear_deg)
info = {
"method": detection["method"],
"shear_degrees": shear_deg,
"confidence": confidence,
}
return corrected, info
def dewarp_image_manual(img: np.ndarray, shear_degrees: float) -> np.ndarray:
"""Apply shear correction with a manual angle.
Args:
img: BGR image (deskewed, before dewarp).
shear_degrees: Shear angle in degrees to correct.
Returns:
Corrected image.
"""
if abs(shear_degrees) < 0.001:
return img
return _apply_shear(img, -shear_degrees)
# =============================================================================
# Stage 4: Dual Image Preparation
# =============================================================================
def create_ocr_image(img: np.ndarray) -> np.ndarray:
"""Create a binarized image optimized for Tesseract OCR.
Steps: Grayscale → Background normalization → Adaptive threshold → Denoise.
Args:
img: BGR image.
Returns:
Binary image (white text on black background inverted to black on white).
"""
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
# Background normalization: divide by blurred version
bg = cv2.GaussianBlur(gray, (51, 51), 0)
normalized = cv2.divide(gray, bg, scale=255)
# Adaptive binarization
binary = cv2.adaptiveThreshold(
normalized, 255, cv2.ADAPTIVE_THRESH_GAUSSIAN_C,
cv2.THRESH_BINARY, 31, 10
)
# Light denoise
denoised = cv2.medianBlur(binary, 3)
return denoised
def create_layout_image(img: np.ndarray) -> np.ndarray:
"""Create a CLAHE-enhanced grayscale image for layout analysis.
Args:
img: BGR image.
Returns:
Enhanced grayscale image.
"""
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
clahe = cv2.createCLAHE(clipLimit=2.0, tileGridSize=(8, 8))
enhanced = clahe.apply(gray)
return enhanced
# =============================================================================
# Stage 5: Layout Analysis (Projection Profiles)
# =============================================================================
def _find_content_bounds(inv: np.ndarray) -> Tuple[int, int, int, int]:
"""Find the bounding box of actual text content (excluding page margins).
Returns:
Tuple of (left_x, right_x, top_y, bottom_y).
"""
h, w = inv.shape[:2]
# Horizontal projection for top/bottom
h_proj = np.sum(inv, axis=1).astype(float) / (w * 255)
top_y = 0
for y in range(h):
if h_proj[y] > 0.005:
top_y = max(0, y - 5)
break
bottom_y = h
for y in range(h - 1, 0, -1):
if h_proj[y] > 0.005:
bottom_y = min(h, y + 5)
break
# Vertical projection for left/right margins
v_proj = np.sum(inv[top_y:bottom_y, :], axis=0).astype(float)
v_proj_norm = v_proj / ((bottom_y - top_y) * 255) if (bottom_y - top_y) > 0 else v_proj
left_x = 0
for x in range(w):
if v_proj_norm[x] > 0.005:
left_x = max(0, x - 2)
break
right_x = w
for x in range(w - 1, 0, -1):
if v_proj_norm[x] > 0.005:
right_x = min(w, x + 2)
break
return left_x, right_x, top_y, bottom_y
def analyze_layout(layout_img: np.ndarray, ocr_img: np.ndarray) -> List[PageRegion]:
"""Detect columns, header, and footer using projection profiles.
Uses content-bounds detection to exclude page margins before searching
for column separators within the actual text area.
Args:
layout_img: CLAHE-enhanced grayscale image.
ocr_img: Binarized image for text density analysis.
Returns:
List of PageRegion objects describing detected regions.
"""
h, w = ocr_img.shape[:2]
# Invert: black text on white → white text on black for projection
inv = cv2.bitwise_not(ocr_img)
# --- Find actual content bounds (exclude page margins) ---
left_x, right_x, top_y, bottom_y = _find_content_bounds(inv)
content_w = right_x - left_x
content_h = bottom_y - top_y
logger.info(f"Layout: content bounds x=[{left_x}..{right_x}] ({content_w}px), "
f"y=[{top_y}..{bottom_y}] ({content_h}px) in {w}x{h} image")
if content_w < w * 0.3 or content_h < h * 0.3:
# Fallback if detection seems wrong
left_x, right_x = 0, w
top_y, bottom_y = 0, h
content_w, content_h = w, h
# --- Vertical projection within content area to find column separators ---
content_strip = inv[top_y:bottom_y, left_x:right_x]
v_proj = np.sum(content_strip, axis=0).astype(float)
v_proj_norm = v_proj / (content_h * 255) if content_h > 0 else v_proj
# Smooth the projection profile
kernel_size = max(5, content_w // 50)
if kernel_size % 2 == 0:
kernel_size += 1
v_proj_smooth = np.convolve(v_proj_norm, np.ones(kernel_size) / kernel_size, mode='same')
# Debug: log projection profile statistics
p_mean = float(np.mean(v_proj_smooth))
p_median = float(np.median(v_proj_smooth))
p_min = float(np.min(v_proj_smooth))
p_max = float(np.max(v_proj_smooth))
logger.info(f"Layout: v_proj stats — min={p_min:.4f}, max={p_max:.4f}, "
f"mean={p_mean:.4f}, median={p_median:.4f}")
# Find valleys using multiple threshold strategies
# Strategy 1: relative to median (catches clear separators)
# Strategy 2: local minima approach (catches subtle gaps)
threshold = max(p_median * 0.3, p_mean * 0.2)
logger.info(f"Layout: valley threshold={threshold:.4f}")
in_valley = v_proj_smooth < threshold
# Find contiguous valley regions
all_valleys = []
start = None
for x in range(len(v_proj_smooth)):
if in_valley[x] and start is None:
start = x
elif not in_valley[x] and start is not None:
valley_width = x - start
valley_depth = float(np.min(v_proj_smooth[start:x]))
# Valley must be at least 3px wide
if valley_width >= 3:
all_valleys.append((start, x, (start + x) // 2, valley_width, valley_depth))
start = None
logger.info(f"Layout: raw valleys (before filter): {len(all_valleys)}"
f"{[(v[0]+left_x, v[1]+left_x, v[3], f'{v[4]:.4f}') for v in all_valleys[:10]]}")
# Filter: valleys must be inside the content area (not at edges)
inner_margin = int(content_w * 0.08)
valleys = [v for v in all_valleys if inner_margin < v[2] < content_w - inner_margin]
# If no valleys found with strict threshold, try local minima approach
if len(valleys) < 2:
logger.info("Layout: trying local minima approach for column detection")
# Divide content into 20 segments, find the 2 lowest
seg_count = 20
seg_width = content_w // seg_count
seg_scores = []
for i in range(seg_count):
sx = i * seg_width
ex = min((i + 1) * seg_width, content_w)
seg_mean = float(np.mean(v_proj_smooth[sx:ex]))
seg_scores.append((i, sx, ex, seg_mean))
seg_scores.sort(key=lambda s: s[3])
logger.info(f"Layout: segment scores (lowest 5): "
f"{[(s[0], s[1]+left_x, s[2]+left_x, f'{s[3]:.4f}') for s in seg_scores[:5]]}")
# Find two lowest non-adjacent segments that create reasonable columns
candidate_valleys = []
for seg_idx, sx, ex, seg_mean in seg_scores:
# Must not be at the edges
if seg_idx <= 1 or seg_idx >= seg_count - 2:
continue
# Must be significantly lower than overall mean
if seg_mean < p_mean * 0.6:
center = (sx + ex) // 2
candidate_valleys.append((sx, ex, center, ex - sx, seg_mean))
if len(candidate_valleys) >= 2:
# Pick the best pair: non-adjacent, creating reasonable column widths
candidate_valleys.sort(key=lambda v: v[2])
best_pair = None
best_score = float('inf')
for i in range(len(candidate_valleys)):
for j in range(i + 1, len(candidate_valleys)):
c1 = candidate_valleys[i][2]
c2 = candidate_valleys[j][2]
# Must be at least 20% apart
if (c2 - c1) < content_w * 0.2:
continue
col1 = c1
col2 = c2 - c1
col3 = content_w - c2
# Each column at least 15%
if col1 < content_w * 0.12 or col2 < content_w * 0.12 or col3 < content_w * 0.12:
continue
parts = sorted([col1, col2, col3])
score = parts[2] - parts[0]
if score < best_score:
best_score = score
best_pair = (candidate_valleys[i], candidate_valleys[j])
if best_pair:
valleys = list(best_pair)
logger.info(f"Layout: local minima found 2 valleys: "
f"{[(v[0]+left_x, v[1]+left_x, v[3]) for v in valleys]}")
logger.info(f"Layout: final {len(valleys)} valleys: "
f"{[(v[0]+left_x, v[1]+left_x, v[3]) for v in valleys]}")
regions = []
if len(valleys) >= 2:
# 3-column layout detected
valleys.sort(key=lambda v: v[2])
if len(valleys) == 2:
sep1_center = valleys[0][2]
sep2_center = valleys[1][2]
else:
# Pick the two valleys that best divide into 3 parts
# Prefer wider valleys (more likely true separators)
best_pair = None
best_score = float('inf')
for i in range(len(valleys)):
for j in range(i + 1, len(valleys)):
c1, c2 = valleys[i][2], valleys[j][2]
# Each column should be at least 15% of content width
col1 = c1
col2 = c2 - c1
col3 = content_w - c2
if col1 < content_w * 0.15 or col2 < content_w * 0.15 or col3 < content_w * 0.15:
continue
# Score: lower is better (more even distribution)
parts = sorted([col1, col2, col3])
score = parts[2] - parts[0]
# Bonus for wider valleys (subtract valley width)
score -= (valleys[i][3] + valleys[j][3]) * 0.5
if score < best_score:
best_score = score
best_pair = (c1, c2)
if best_pair:
sep1_center, sep2_center = best_pair
else:
sep1_center = valleys[0][2]
sep2_center = valleys[1][2]
# Convert from content-relative to absolute coordinates
abs_sep1 = sep1_center + left_x
abs_sep2 = sep2_center + left_x
logger.info(f"Layout: 3 columns at separators x={abs_sep1}, x={abs_sep2} "
f"(widths: {abs_sep1}, {abs_sep2-abs_sep1}, {w-abs_sep2})")
regions.append(PageRegion(
type='column_en', x=0, y=top_y,
width=abs_sep1, height=content_h
))
regions.append(PageRegion(
type='column_de', x=abs_sep1, y=top_y,
width=abs_sep2 - abs_sep1, height=content_h
))
regions.append(PageRegion(
type='column_example', x=abs_sep2, y=top_y,
width=w - abs_sep2, height=content_h
))
elif len(valleys) == 1:
# 2-column layout
abs_sep = valleys[0][2] + left_x
logger.info(f"Layout: 2 columns at separator x={abs_sep}")
regions.append(PageRegion(
type='column_en', x=0, y=top_y,
width=abs_sep, height=content_h
))
regions.append(PageRegion(
type='column_de', x=abs_sep, y=top_y,
width=w - abs_sep, height=content_h
))
else:
# No columns detected — run full-page OCR as single column
logger.warning("Layout: no column separators found, using full page")
regions.append(PageRegion(
type='column_en', x=0, y=top_y,
width=w, height=content_h
))
# Add header/footer info
if top_y > 10:
regions.append(PageRegion(
type='header', x=0, y=0,
width=w, height=top_y
))
if bottom_y < h - 10:
regions.append(PageRegion(
type='footer', x=0, y=bottom_y,
width=w, height=h - bottom_y
))
col_count = len([r for r in regions if r.type.startswith('column')])
logger.info(f"Layout: {col_count} columns, "
f"header={'yes' if top_y > 10 else 'no'}, "
f"footer={'yes' if bottom_y < h - 10 else 'no'}")
return regions
# =============================================================================
# Stage 6: Multi-Pass OCR
# =============================================================================
def ocr_region(ocr_img: np.ndarray, region: PageRegion, lang: str,
psm: int, fallback_psm: Optional[int] = None,
min_confidence: float = 40.0) -> List[Dict[str, Any]]:
"""Run Tesseract OCR on a specific region with given PSM.
Args:
ocr_img: Binarized full-page image.
region: Region to crop and OCR.
lang: Tesseract language string.
psm: Page Segmentation Mode.
fallback_psm: If confidence too low, retry with this PSM per line.
min_confidence: Minimum average confidence before fallback.
Returns:
List of word dicts with text, position, confidence.
"""
# Crop region
crop = ocr_img[region.y:region.y + region.height,
region.x:region.x + region.width]
if crop.size == 0:
return []
# Convert to PIL for pytesseract
pil_img = Image.fromarray(crop)
# Run Tesseract with specified PSM
config = f'--psm {psm} --oem 3'
try:
data = pytesseract.image_to_data(pil_img, lang=lang, config=config,
output_type=pytesseract.Output.DICT)
except Exception as e:
logger.warning(f"Tesseract failed for region {region.type}: {e}")
return []
words = []
for i in range(len(data['text'])):
text = data['text'][i].strip()
conf = int(data['conf'][i])
if not text or conf < 10:
continue
words.append({
'text': text,
'left': data['left'][i] + region.x, # Absolute coords
'top': data['top'][i] + region.y,
'width': data['width'][i],
'height': data['height'][i],
'conf': conf,
'region_type': region.type,
})
# Check average confidence
if words and fallback_psm is not None:
avg_conf = sum(w['conf'] for w in words) / len(words)
if avg_conf < min_confidence:
logger.info(f"Region {region.type}: avg confidence {avg_conf:.0f}% < {min_confidence}%, "
f"trying fallback PSM {fallback_psm}")
words = _ocr_region_line_by_line(ocr_img, region, lang, fallback_psm)
return words
def _ocr_region_line_by_line(ocr_img: np.ndarray, region: PageRegion,
lang: str, psm: int) -> List[Dict[str, Any]]:
"""OCR a region line by line (fallback for low-confidence regions).
Splits the region into horizontal strips based on text density,
then OCRs each strip individually with the given PSM.
"""
crop = ocr_img[region.y:region.y + region.height,
region.x:region.x + region.width]
if crop.size == 0:
return []
# Find text lines via horizontal projection
inv = cv2.bitwise_not(crop)
h_proj = np.sum(inv, axis=1)
threshold = np.max(h_proj) * 0.05 if np.max(h_proj) > 0 else 0
# Find line boundaries
lines = []
in_text = False
line_start = 0
for y in range(len(h_proj)):
if h_proj[y] > threshold and not in_text:
line_start = y
in_text = True
elif h_proj[y] <= threshold and in_text:
if y - line_start > 5: # Minimum line height
lines.append((line_start, y))
in_text = False
if in_text and len(h_proj) - line_start > 5:
lines.append((line_start, len(h_proj)))
all_words = []
config = f'--psm {psm} --oem 3'
for line_y_start, line_y_end in lines:
# Add small padding
pad = 3
y1 = max(0, line_y_start - pad)
y2 = min(crop.shape[0], line_y_end + pad)
line_crop = crop[y1:y2, :]
if line_crop.size == 0:
continue
pil_img = Image.fromarray(line_crop)
try:
data = pytesseract.image_to_data(pil_img, lang=lang, config=config,
output_type=pytesseract.Output.DICT)
except Exception:
continue
for i in range(len(data['text'])):
text = data['text'][i].strip()
conf = int(data['conf'][i])
if not text or conf < 10:
continue
all_words.append({
'text': text,
'left': data['left'][i] + region.x,
'top': data['top'][i] + region.y + y1,
'width': data['width'][i],
'height': data['height'][i],
'conf': conf,
'region_type': region.type,
})
return all_words
def run_multi_pass_ocr(ocr_img: np.ndarray,
regions: List[PageRegion],
lang: str = "eng+deu") -> Dict[str, List[Dict]]:
"""Run OCR on each detected region with optimized settings.
Args:
ocr_img: Binarized full-page image.
regions: Detected page regions.
lang: Default language.
Returns:
Dict mapping region type to list of word dicts.
"""
results: Dict[str, List[Dict]] = {}
for region in regions:
if region.type == 'header' or region.type == 'footer':
continue # Skip non-content regions
if region.type == 'column_en':
words = ocr_region(ocr_img, region, lang='eng', psm=4)
elif region.type == 'column_de':
words = ocr_region(ocr_img, region, lang='deu', psm=4)
elif region.type == 'column_example':
words = ocr_region(ocr_img, region, lang=lang, psm=6,
fallback_psm=7, min_confidence=40.0)
else:
words = ocr_region(ocr_img, region, lang=lang, psm=6)
results[region.type] = words
logger.info(f"OCR {region.type}: {len(words)} words")
return results
# =============================================================================
# Stage 7: Line Alignment → Vocabulary Entries
# =============================================================================
def _group_words_into_lines(words: List[Dict], y_tolerance_px: int = 20) -> List[List[Dict]]:
"""Group words by Y position into lines, sorted by X within each line."""
if not words:
return []
sorted_words = sorted(words, key=lambda w: (w['top'], w['left']))
lines: List[List[Dict]] = []
current_line: List[Dict] = [sorted_words[0]]
current_y = sorted_words[0]['top']
for word in sorted_words[1:]:
if abs(word['top'] - current_y) <= y_tolerance_px:
current_line.append(word)
else:
current_line.sort(key=lambda w: w['left'])
lines.append(current_line)
current_line = [word]
current_y = word['top']
if current_line:
current_line.sort(key=lambda w: w['left'])
lines.append(current_line)
return lines
def match_lines_to_vocab(ocr_results: Dict[str, List[Dict]],
regions: List[PageRegion],
y_tolerance_px: int = 25) -> List[VocabRow]:
"""Align OCR results from different columns into vocabulary rows.
Uses Y-coordinate matching to pair English words, German translations,
and example sentences that appear on the same line.
Args:
ocr_results: Dict mapping region type to word lists.
regions: Detected regions (for reference).
y_tolerance_px: Max Y-distance to consider words on the same row.
Returns:
List of VocabRow objects.
"""
# Group words into lines per column
en_lines = _group_words_into_lines(ocr_results.get('column_en', []), y_tolerance_px)
de_lines = _group_words_into_lines(ocr_results.get('column_de', []), y_tolerance_px)
ex_lines = _group_words_into_lines(ocr_results.get('column_example', []), y_tolerance_px)
def line_y_center(line: List[Dict]) -> float:
return sum(w['top'] + w['height'] / 2 for w in line) / len(line)
def line_text(line: List[Dict]) -> str:
return ' '.join(w['text'] for w in line)
def line_confidence(line: List[Dict]) -> float:
return sum(w['conf'] for w in line) / len(line) if line else 0
# Build EN entries as the primary reference
vocab_rows: List[VocabRow] = []
for en_line in en_lines:
en_y = line_y_center(en_line)
en_text = line_text(en_line)
en_conf = line_confidence(en_line)
# Skip very short or likely header content
if len(en_text.strip()) < 2:
continue
# Find matching DE line
de_text = ""
de_conf = 0.0
best_de_dist = float('inf')
best_de_idx = -1
for idx, de_line in enumerate(de_lines):
dist = abs(line_y_center(de_line) - en_y)
if dist < y_tolerance_px and dist < best_de_dist:
best_de_dist = dist
best_de_idx = idx
if best_de_idx >= 0:
de_text = line_text(de_lines[best_de_idx])
de_conf = line_confidence(de_lines[best_de_idx])
# Find matching example line
ex_text = ""
ex_conf = 0.0
best_ex_dist = float('inf')
best_ex_idx = -1
for idx, ex_line in enumerate(ex_lines):
dist = abs(line_y_center(ex_line) - en_y)
if dist < y_tolerance_px and dist < best_ex_dist:
best_ex_dist = dist
best_ex_idx = idx
if best_ex_idx >= 0:
ex_text = line_text(ex_lines[best_ex_idx])
ex_conf = line_confidence(ex_lines[best_ex_idx])
avg_conf = en_conf
conf_count = 1
if de_conf > 0:
avg_conf += de_conf
conf_count += 1
if ex_conf > 0:
avg_conf += ex_conf
conf_count += 1
vocab_rows.append(VocabRow(
english=en_text.strip(),
german=de_text.strip(),
example=ex_text.strip(),
confidence=avg_conf / conf_count,
y_position=int(en_y),
))
# Handle multi-line wrapping in example column:
# If an example line has no matching EN/DE, append to previous entry
matched_ex_ys = set()
for row in vocab_rows:
if row.example:
matched_ex_ys.add(row.y_position)
for ex_line in ex_lines:
ex_y = line_y_center(ex_line)
# Check if already matched
already_matched = any(abs(ex_y - y) < y_tolerance_px for y in matched_ex_ys)
if already_matched:
continue
# Find nearest previous vocab row
best_row = None
best_dist = float('inf')
for row in vocab_rows:
dist = ex_y - row.y_position
if 0 < dist < y_tolerance_px * 3 and dist < best_dist:
best_dist = dist
best_row = row
if best_row:
continuation = line_text(ex_line).strip()
if continuation:
best_row.example = (best_row.example + " " + continuation).strip()
# Sort by Y position
vocab_rows.sort(key=lambda r: r.y_position)
return vocab_rows
# =============================================================================
# Stage 8: Optional LLM Post-Correction
# =============================================================================
async def llm_post_correct(img: np.ndarray, vocab_rows: List[VocabRow],
confidence_threshold: float = 50.0,
enabled: bool = False) -> List[VocabRow]:
"""Optionally send low-confidence regions to Qwen-VL for correction.
Default: disabled. Enable per parameter.
Args:
img: Original BGR image.
vocab_rows: Current vocabulary rows.
confidence_threshold: Rows below this get LLM correction.
enabled: Whether to actually run LLM correction.
Returns:
Corrected vocabulary rows.
"""
if not enabled:
return vocab_rows
# TODO: Implement Qwen-VL correction for low-confidence entries
# For each row with confidence < threshold:
# 1. Crop the relevant region from img
# 2. Send crop + OCR text to Qwen-VL
# 3. Replace text if LLM provides a confident correction
logger.info(f"LLM post-correction skipped (not yet implemented)")
return vocab_rows
# =============================================================================
# Orchestrator
# =============================================================================
async def run_cv_pipeline(
pdf_data: Optional[bytes] = None,
image_data: Optional[bytes] = None,
page_number: int = 0,
zoom: float = 3.0,
enable_dewarp: bool = True,
enable_llm_correction: bool = False,
lang: str = "eng+deu",
) -> PipelineResult:
"""Run the complete CV document reconstruction pipeline.
Args:
pdf_data: Raw PDF bytes (mutually exclusive with image_data).
image_data: Raw image bytes (mutually exclusive with pdf_data).
page_number: 0-indexed page number (for PDF).
zoom: PDF rendering zoom factor.
enable_dewarp: Whether to run dewarp stage.
enable_llm_correction: Whether to run LLM post-correction.
lang: Tesseract language string.
Returns:
PipelineResult with vocabulary and timing info.
"""
if not CV_PIPELINE_AVAILABLE:
return PipelineResult(error="CV pipeline not available (OpenCV or Tesseract missing)")
result = PipelineResult()
total_start = time.time()
try:
# Stage 1: Render
t = time.time()
if pdf_data:
img = render_pdf_high_res(pdf_data, page_number, zoom)
elif image_data:
img = render_image_high_res(image_data)
else:
return PipelineResult(error="No input data (pdf_data or image_data required)")
result.stages['render'] = round(time.time() - t, 2)
result.image_width = img.shape[1]
result.image_height = img.shape[0]
logger.info(f"Stage 1 (render): {img.shape[1]}x{img.shape[0]} in {result.stages['render']}s")
# Stage 2: Deskew
t = time.time()
img, angle = deskew_image(img)
result.stages['deskew'] = round(time.time() - t, 2)
logger.info(f"Stage 2 (deskew): {angle:.2f}° in {result.stages['deskew']}s")
# Stage 3: Dewarp
if enable_dewarp:
t = time.time()
img = dewarp_image(img)
result.stages['dewarp'] = round(time.time() - t, 2)
# Stage 4: Dual image preparation
t = time.time()
ocr_img = create_ocr_image(img)
layout_img = create_layout_image(img)
result.stages['image_prep'] = round(time.time() - t, 2)
# Stage 5: Layout analysis
t = time.time()
regions = analyze_layout(layout_img, ocr_img)
result.stages['layout'] = round(time.time() - t, 2)
result.columns_detected = len([r for r in regions if r.type.startswith('column')])
logger.info(f"Stage 5 (layout): {result.columns_detected} columns in {result.stages['layout']}s")
# Stage 6: Multi-pass OCR
t = time.time()
ocr_results = run_multi_pass_ocr(ocr_img, regions, lang)
result.stages['ocr'] = round(time.time() - t, 2)
total_words = sum(len(w) for w in ocr_results.values())
result.word_count = total_words
logger.info(f"Stage 6 (OCR): {total_words} words in {result.stages['ocr']}s")
# Stage 7: Line alignment
t = time.time()
vocab_rows = match_lines_to_vocab(ocr_results, regions)
result.stages['alignment'] = round(time.time() - t, 2)
# Stage 8: Optional LLM correction
if enable_llm_correction:
t = time.time()
vocab_rows = await llm_post_correct(img, vocab_rows)
result.stages['llm_correction'] = round(time.time() - t, 2)
# Convert to output format
result.vocabulary = [
{
"english": row.english,
"german": row.german,
"example": row.example,
"confidence": round(row.confidence, 1),
}
for row in vocab_rows
if row.english or row.german # Skip empty rows
]
result.duration_seconds = round(time.time() - total_start, 2)
logger.info(f"CV Pipeline complete: {len(result.vocabulary)} entries in {result.duration_seconds}s")
except Exception as e:
logger.error(f"CV Pipeline error: {e}")
import traceback
logger.debug(traceback.format_exc())
result.error = str(e)
result.duration_seconds = round(time.time() - total_start, 2)
return result