Slide Visualization

Visualization

Overview

Histolab provides several built-in visualization methods to help inspect slides, preview tile locations, visualize masks, and assess extraction quality. Proper visualization is essential for validating preprocessing pipelines, debugging extraction issues, and presenting results.

Slide Visualization

Thumbnail Display

from histolab.slide import Slide
import matplotlib.pyplot as plt

slide = Slide("slide.svs", processed_path="output/")

# Display thumbnail
plt.figure(figsize=(10, 10))
plt.imshow(slide.thumbnail)
plt.title(f"Slide: {slide.name}")
plt.axis('off')
plt.show()

Save Thumbnail to Disk

# Save thumbnail as image file
slide.save_thumbnail()
# Saves to processed_path/thumbnails/slide_name_thumb.png

Scaled Images

# Get scaled version of slide at specific downsample factor
scaled_img = slide.scaled_image(scale_factor=32)

plt.imshow(scaled_img)
plt.title(f"Slide at 32x downsample")
plt.show()

Mask Visualization

Using locate_mask()

from histolab.masks import TissueMask, BiggestTissueBoxMask

# Visualize TissueMask
tissue_mask = TissueMask()
slide.locate_mask(tissue_mask)

# Visualize BiggestTissueBoxMask
biggest_mask = BiggestTissueBoxMask()
slide.locate_mask(biggest_mask)

This displays the slide thumbnail with mask boundaries overlaid in red.

Manual Mask Visualization

import matplotlib.pyplot as plt
from histolab.masks import TissueMask

slide = Slide("slide.svs", processed_path="output/")
mask = TissueMask()

# Generate mask
mask_array = mask(slide)

# Create side-by-side comparison
fig, axes = plt.subplots(1, 3, figsize=(20, 7))

# Original thumbnail
axes[0].imshow(slide.thumbnail)
axes[0].set_title("Original Slide")
axes[0].axis('off')

# Binary mask
axes[1].imshow(mask_array, cmap='gray')
axes[1].set_title("Tissue Mask")
axes[1].axis('off')

# Overlay mask on thumbnail
from matplotlib.colors import ListedColormap
overlay = slide.thumbnail.copy()
axes[2].imshow(overlay)
axes[2].imshow(mask_array, cmap=ListedColormap(['none', 'red']), alpha=0.3)
axes[2].set_title("Mask Overlay")
axes[2].axis('off')

plt.tight_layout()
plt.show()

Comparing Multiple Masks

from histolab.masks import TissueMask, BiggestTissueBoxMask

masks = {
    'TissueMask': TissueMask(),
    'BiggestTissueBoxMask': BiggestTissueBoxMask()
}

fig, axes = plt.subplots(1, len(masks) + 1, figsize=(20, 6))

# Original
axes[0].imshow(slide.thumbnail)
axes[0].set_title("Original")
axes[0].axis('off')

# Each mask
for idx, (name, mask) in enumerate(masks.items(), 1):
    mask_array = mask(slide)
    axes[idx].imshow(mask_array, cmap='gray')
    axes[idx].set_title(name)
    axes[idx].axis('off')

plt.tight_layout()
plt.show()

Tile Location Preview

Using locate_tiles()

Preview tile locations before extraction:

from histolab.tiler import RandomTiler, GridTiler, ScoreTiler
from histolab.scorer import NucleiScorer

# RandomTiler preview
random_tiler = RandomTiler(
    tile_size=(512, 512),
    n_tiles=50,
    level=0,
    seed=42
)
random_tiler.locate_tiles(slide, n_tiles=20)

# GridTiler preview
grid_tiler = GridTiler(
    tile_size=(512, 512),
    level=0
)
grid_tiler.locate_tiles(slide)

# ScoreTiler preview
score_tiler = ScoreTiler(
    tile_size=(512, 512),
    n_tiles=30,
    scorer=NucleiScorer()
)
score_tiler.locate_tiles(slide, n_tiles=15)

This displays colored rectangles on the slide thumbnail indicating where tiles will be extracted.

Custom Tile Location Visualization

import matplotlib.pyplot as plt
import matplotlib.patches as patches
from histolab.tiler import RandomTiler

slide = Slide("slide.svs", processed_path="output/")
tiler = RandomTiler(tile_size=(512, 512), n_tiles=30, seed=42)

# Get thumbnail and scale factor
thumbnail = slide.thumbnail
scale_factor = slide.dimensions[0] / thumbnail.size[0]

# Generate tile coordinates (without extracting)
fig, ax = plt.subplots(figsize=(12, 12))
ax.imshow(thumbnail)
ax.set_title("Tile Locations Preview")
ax.axis('off')

# Manually add rectangles for each tile location
# Note: This is conceptual - actual implementation would retrieve coordinates from tiler
tile_coords = []  # Would be populated by tiler logic
for coord in tile_coords:
    x, y = coord[0] / scale_factor, coord[1] / scale_factor
    w, h = 512 / scale_factor, 512 / scale_factor
    rect = patches.Rectangle((x, y), w, h,
                             linewidth=2, edgecolor='red',
                             facecolor='none')
    ax.add_patch(rect)

plt.show()

Tile Visualization

Display Extracted Tiles

from pathlib import Path
from PIL import Image
import matplotlib.pyplot as plt

tile_dir = Path("output/tiles/")
tile_paths = list(tile_dir.glob("*.png"))[:16]  # First 16 tiles

fig, axes = plt.subplots(4, 4, figsize=(12, 12))
axes = axes.ravel()

for idx, tile_path in enumerate(tile_paths):
    tile_img = Image.open(tile_path)
    axes[idx].imshow(tile_img)
    axes[idx].set_title(tile_path.stem, fontsize=8)
    axes[idx].axis('off')

plt.tight_layout()
plt.show()

Tile Grid Mosaic

def create_tile_mosaic(tile_dir, grid_size=(4, 4)):
    """Create mosaic of tiles."""
    tile_paths = list(Path(tile_dir).glob("*.png"))[:grid_size[0] * grid_size[1]]

    fig, axes = plt.subplots(grid_size[0], grid_size[1], figsize=(16, 16))

    for idx, tile_path in enumerate(tile_paths):
        row = idx // grid_size[1]
        col = idx % grid_size[1]
        tile_img = Image.open(tile_path)
        axes[row, col].imshow(tile_img)
        axes[row, col].axis('off')

    plt.tight_layout()
    plt.savefig("tile_mosaic.png", dpi=150, bbox_inches='tight')
    plt.show()

create_tile_mosaic("output/tiles/", grid_size=(5, 5))

Tile with Tissue Mask Overlay

from histolab.tile import Tile
import matplotlib.pyplot as plt

# Assume we have a tile object
tile = Tile(image=pil_image, coords=(x, y))

# Calculate tissue mask
tile.calculate_tissue_mask()

fig, axes = plt.subplots(1, 3, figsize=(15, 5))

# Original tile
axes[0].imshow(tile.image)
axes[0].set_title("Original Tile")
axes[0].axis('off')

# Tissue mask
axes[1].imshow(tile.tissue_mask, cmap='gray')
axes[1].set_title(f"Tissue Mask ({tile.tissue_ratio:.1%} tissue)")
axes[1].axis('off')

# Overlay
axes[2].imshow(tile.image)
axes[2].imshow(tile.tissue_mask, cmap='Reds', alpha=0.3)
axes[2].set_title("Overlay")
axes[2].axis('off')

plt.tight_layout()
plt.show()

Quality Assessment Visualization

Tile Score Distribution

import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns

# Load tile report from ScoreTiler
report_df = pd.read_csv("tiles_report.csv")

# Score distribution histogram
plt.figure(figsize=(10, 6))
plt.hist(report_df['score'], bins=30, edgecolor='black', alpha=0.7)
plt.xlabel('Tile Score')
plt.ylabel('Frequency')
plt.title('Distribution of Tile Scores')
plt.grid(axis='y', alpha=0.3)
plt.show()

# Score vs tissue percentage scatter
plt.figure(figsize=(10, 6))
plt.scatter(report_df['tissue_percent'], report_df['score'], alpha=0.5)
plt.xlabel('Tissue Percentage')
plt.ylabel('Tile Score')
plt.title('Tile Score vs Tissue Coverage')
plt.grid(alpha=0.3)
plt.show()

Top vs Bottom Scoring Tiles

import pandas as pd
from PIL import Image
import matplotlib.pyplot as plt

# Load tile report
report_df = pd.read_csv("tiles_report.csv")
report_df = report_df.sort_values('score', ascending=False)

# Top 8 tiles
top_tiles = report_df.head(8)
# Bottom 8 tiles
bottom_tiles = report_df.tail(8)

fig, axes = plt.subplots(2, 8, figsize=(20, 6))

# Display top tiles
for idx, (_, row) in enumerate(top_tiles.iterrows()):
    tile_img = Image.open(f"output/tiles/{row['tile_name']}")
    axes[0, idx].imshow(tile_img)
    axes[0, idx].set_title(f"Score: {row['score']:.3f}", fontsize=8)
    axes[0, idx].axis('off')

# Display bottom tiles
for idx, (_, row) in enumerate(bottom_tiles.iterrows()):
    tile_img = Image.open(f"output/tiles/{row['tile_name']}")
    axes[1, idx].imshow(tile_img)
    axes[1, idx].set_title(f"Score: {row['score']:.3f}", fontsize=8)
    axes[1, idx].axis('off')

axes[0, 0].set_ylabel('Top Scoring', fontsize=12)
axes[1, 0].set_ylabel('Bottom Scoring', fontsize=12)

plt.tight_layout()
plt.savefig("score_comparison.png", dpi=150, bbox_inches='tight')
plt.show()

Multi-Slide Visualization

Slide Collection Thumbnails

from pathlib import Path
from histolab.slide import Slide
import matplotlib.pyplot as plt

slide_dir = Path("slides/")
slide_paths = list(slide_dir.glob("*.svs"))[:9]

fig, axes = plt.subplots(3, 3, figsize=(15, 15))
axes = axes.ravel()

for idx, slide_path in enumerate(slide_paths):
    slide = Slide(slide_path, processed_path="output/")
    axes[idx].imshow(slide.thumbnail)
    axes[idx].set_title(slide.name, fontsize=10)
    axes[idx].axis('off')

plt.tight_layout()
plt.savefig("slide_collection.png", dpi=150, bbox_inches='tight')
plt.show()

Tissue Coverage Comparison

from pathlib import Path
from histolab.slide import Slide
from histolab.masks import TissueMask
import matplotlib.pyplot as plt
import numpy as np

slide_paths = list(Path("slides/").glob("*.svs"))
tissue_percentages = []
slide_names = []

for slide_path in slide_paths:
    slide = Slide(slide_path, processed_path="output/")
    mask = TissueMask()(slide)
    tissue_pct = mask.sum() / mask.size * 100
    tissue_percentages.append(tissue_pct)
    slide_names.append(slide.name)

# Bar plot
plt.figure(figsize=(12, 6))
plt.bar(range(len(slide_names)), tissue_percentages)
plt.xticks(range(len(slide_names)), slide_names, rotation=45, ha='right')
plt.ylabel('Tissue Coverage (%)')
plt.title('Tissue Coverage Across Slides')
plt.grid(axis='y', alpha=0.3)
plt.tight_layout()
plt.show()

Filter Effect Visualization

Before and After Filtering

from histolab.filters.image_filters import RgbToGrayscale, HistogramEqualization
from histolab.filters.compositions import Compose

# Define filter pipeline
filter_pipeline = Compose([
    RgbToGrayscale(),
    HistogramEqualization()
])

# Original vs filtered
fig, axes = plt.subplots(1, 2, figsize=(12, 6))

axes[0].imshow(slide.thumbnail)
axes[0].set_title("Original")
axes[0].axis('off')

filtered = filter_pipeline(slide.thumbnail)
axes[1].imshow(filtered, cmap='gray')
axes[1].set_title("After Filtering")
axes[1].axis('off')

plt.tight_layout()
plt.show()

Multi-Step Filter Visualization

from histolab.filters.image_filters import RgbToGrayscale, OtsuThreshold
from histolab.filters.morphological_filters import BinaryDilation, RemoveSmallObjects

# Individual filter steps
steps = [
    ("Original", None),
    ("Grayscale", RgbToGrayscale()),
    ("Otsu Threshold", Compose([RgbToGrayscale(), OtsuThreshold()])),
    ("After Dilation", Compose([RgbToGrayscale(), OtsuThreshold(), BinaryDilation(disk_size=5)])),
    ("Remove Small Objects", Compose([RgbToGrayscale(), OtsuThreshold(), BinaryDilation(disk_size=5), RemoveSmallObjects(area_threshold=500)]))
]

fig, axes = plt.subplots(1, len(steps), figsize=(20, 4))

for idx, (title, filter_fn) in enumerate(steps):
    if filter_fn is None:
        axes[idx].imshow(slide.thumbnail)
    else:
        result = filter_fn(slide.thumbnail)
        axes[idx].imshow(result, cmap='gray')
    axes[idx].set_title(title, fontsize=10)
    axes[idx].axis('off')

plt.tight_layout()
plt.show()

Exporting Visualizations

High-Resolution Exports

# Export high-resolution figure
fig, ax = plt.subplots(figsize=(20, 20))
ax.imshow(slide.thumbnail)
ax.axis('off')
plt.savefig("slide_high_res.png", dpi=300, bbox_inches='tight', pad_inches=0)
plt.close()

PDF Reports

from matplotlib.backends.backend_pdf import PdfPages

# Create multi-page PDF report
with PdfPages('slide_report.pdf') as pdf:
    # Page 1: Slide thumbnail
    fig1, ax1 = plt.subplots(figsize=(10, 10))
    ax1.imshow(slide.thumbnail)
    ax1.set_title(f"Slide: {slide.name}")
    ax1.axis('off')
    pdf.savefig(fig1, bbox_inches='tight')
    plt.close()

    # Page 2: Tissue mask
    fig2, ax2 = plt.subplots(figsize=(10, 10))
    mask = TissueMask()(slide)
    ax2.imshow(mask, cmap='gray')
    ax2.set_title("Tissue Mask")
    ax2.axis('off')
    pdf.savefig(fig2, bbox_inches='tight')
    plt.close()

    # Page 3: Tile locations
    fig3, ax3 = plt.subplots(figsize=(10, 10))
    tiler = RandomTiler(tile_size=(512, 512), n_tiles=30)
    tiler.locate_tiles(slide)
    pdf.savefig(fig3, bbox_inches='tight')
    plt.close()

Interactive Visualization (Jupyter)

IPython Widgets for Exploration

from ipywidgets import interact, IntSlider
import matplotlib.pyplot as plt
from histolab.filters.morphological_filters import BinaryDilation

@interact(disk_size=IntSlider(min=1, max=20, value=5))
def explore_dilation(disk_size):
    """Interactive dilation exploration."""
    filter_pipeline = Compose([
        RgbToGrayscale(),
        OtsuThreshold(),
        BinaryDilation(disk_size=disk_size)
    ])
    result = filter_pipeline(slide.thumbnail)

    plt.figure(figsize=(10, 10))
    plt.imshow(result, cmap='gray')
    plt.title(f"Binary Dilation (disk_size={disk_size})")
    plt.axis('off')
    plt.show()

Best Practices

1. Always preview before processing: Use thumbnails and locate_tiles() to validate settings
2. Use side-by-side comparisons: Show before/after for filter effects
3. Label clearly: Include titles, axes labels, and legends
4. Export high-resolution: Use 300 DPI for publication-quality figures
5. Save intermediate visualizations: Document processing steps
6. Use colormaps appropriately: 'gray' for binary masks, 'viridis' for heatmaps
7. Create reusable visualization functions: Standardize reporting across projects