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Henrik Jess Nielsen
2026-06-01 23:40:55 +02:00
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docs/snippets/php/ocr/image_preprocessing.php Normal file
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```php title="image_preprocessing.php"
<?php
declare(strict_types=1);
/**
* Image Preprocessing for OCR
*
* Improve OCR accuracy by preprocessing images before text recognition.
* Useful for poor quality scans, photos, and challenging documents.
*/
require_once __DIR__ . '/vendor/autoload.php';
use Kreuzberg\Kreuzberg;
use Kreuzberg\Config\ExtractionConfig;
use Kreuzberg\Config\OcrConfig;
use Kreuzberg\Config\ImagePreprocessingConfig;
$config = new ExtractionConfig(
ocr: new OcrConfig(
backend: 'tesseract',
language: 'eng',
imagePreprocessing: new ImagePreprocessingConfig(
denoise: true,
sharpen: true
)
)
);
$kreuzberg = new Kreuzberg($config);
$result = $kreuzberg->extractFile('noisy_scan.pdf');
echo "Basic Preprocessing Results:\n";
echo str_repeat('=', 60) . "\n";
echo substr($result->content, 0, 300) . "...\n\n";
$highDpiConfig = new ExtractionConfig(
ocr: new OcrConfig(
backend: 'tesseract',
language: 'eng',
imagePreprocessing: new ImagePreprocessingConfig(
targetDpi: 400,
denoise: true,
sharpen: true
)
)
);
$kreuzberg = new Kreuzberg($highDpiConfig);
$result = $kreuzberg->extractFile('small_text_scan.pdf');
echo "High DPI Preprocessing:\n";
echo str_repeat('=', 60) . "\n";
echo "Characters extracted: " . strlen($result->content) . "\n";
echo "Preview: " . substr($result->content, 0, 200) . "...\n\n";
$deskewConfig = new ExtractionConfig(
ocr: new OcrConfig(
backend: 'tesseract',
language: 'eng',
imagePreprocessing: new ImagePreprocessingConfig(
deskew: true,
autoRotate: true,
targetDpi: 300
)
)
);
$kreuzberg = new Kreuzberg($deskewConfig);
$result = $kreuzberg->extractFile('crooked_scan.pdf');
echo "Deskewed OCR Results:\n";
echo str_repeat('=', 60) . "\n";
echo $result->content . "\n\n";
$cleanConfig = new ExtractionConfig(
ocr: new OcrConfig(
backend: 'tesseract',
language: 'eng',
imagePreprocessing: new ImagePreprocessingConfig(
removeBackground: true,
denoise: true,
targetDpi: 300
)
)
);
$kreuzberg = new Kreuzberg($cleanConfig);
$result = $kreuzberg->extractFile('watermarked_document.pdf');
echo "Background Removal Results:\n";
echo str_repeat('=', 60) . "\n";
echo "Extracted " . strlen($result->content) . " characters\n";
echo "Text quality improved by removing background noise\n\n";
$comprehensiveConfig = new ExtractionConfig(
ocr: new OcrConfig(
backend: 'tesseract',
language: 'eng',
imagePreprocessing: new ImagePreprocessingConfig(
targetDpi: 400,
denoise: true,
sharpen: true,
autoRotate: true,
deskew: true,
removeBackground: true,
contrastEnhancement: true,
binarize: true
)
)
);
$kreuzberg = new Kreuzberg($comprehensiveConfig);
$result = $kreuzberg->extractFile('very_poor_quality.pdf');
echo "Comprehensive Preprocessing:\n";
echo str_repeat('=', 60) . "\n";
echo "Original quality: Very Poor\n";
echo "After preprocessing:\n";
echo " Characters: " . strlen($result->content) . "\n";
echo " Content preview:\n";
echo " " . substr($result->content, 0, 300) . "...\n\n";
$testFile = 'test_scan.pdf';
if (file_exists($testFile)) {
$configs = [
'No preprocessing' => new ExtractionConfig(
ocr: new OcrConfig(backend: 'tesseract', language: 'eng')
),
'Denoise only' => new ExtractionConfig(
ocr: new OcrConfig(
backend: 'tesseract',
language: 'eng',
imagePreprocessing: new ImagePreprocessingConfig(denoise: true)
)
),
'Denoise + Sharpen' => new ExtractionConfig(
ocr: new OcrConfig(
backend: 'tesseract',
language: 'eng',
imagePreprocessing: new ImagePreprocessingConfig(
denoise: true,
sharpen: true
)
)
),
'Full preprocessing' => $comprehensiveConfig,
];
echo "Preprocessing Comparison:\n";
echo str_repeat('=', 60) . "\n";
foreach ($configs as $name => $config) {
$kreuzberg = new Kreuzberg($config);
$start = microtime(true);
$result = $kreuzberg->extractFile($testFile);
$elapsed = microtime(true) - $start;
echo "$name:\n";
echo " Time: " . number_format($elapsed, 3) . "s\n";
echo " Characters: " . strlen($result->content) . "\n";
echo " Tables: " . count($result->tables) . "\n\n";
}
}
function getOptimalPreprocessing(string $file): ImagePreprocessingConfig
{
$quickScan = new Kreuzberg(new ExtractionConfig(
ocr: new OcrConfig(backend: 'tesseract', language: 'eng')
));
$quickResult = $quickScan->extractFile($file);
$fileSize = filesize($file);
$contentLength = strlen($quickResult->content);
$ratio = $contentLength / $fileSize;
if ($ratio < 0.01) {
return new ImagePreprocessingConfig(
targetDpi: 400,
denoise: true,
sharpen: true,
autoRotate: true,
deskew: true,
removeBackground: true,
contrastEnhancement: true
);
} elseif ($ratio < 0.05) {
return new ImagePreprocessingConfig(
targetDpi: 300,
denoise: true,
sharpen: true,
deskew: true
);
} else {
return new ImagePreprocessingConfig(
targetDpi: 300,
denoise: true
);
}
}
$file = 'auto_detect_quality.pdf';
if (file_exists($file)) {
$preprocessing = getOptimalPreprocessing($file);
$config = new ExtractionConfig(
ocr: new OcrConfig(
backend: 'tesseract',
language: 'eng',
imagePreprocessing: $preprocessing
)
);
$kreuzberg = new Kreuzberg($config);
$result = $kreuzberg->extractFile($file);
echo "Adaptive preprocessing applied\n";
echo "Result: " . strlen($result->content) . " characters extracted\n";
}
```