Whether your document originates from a scanner or a camera, Adobe Acrobat’s Enhance Scans tool offers a powerful solution to significantly improve the quality, readability, and searchability of your PDF documents. Starting with a simple JPEG file that was previously scanned, but you can also initiate the process directly from your scanner using the Create PDF tool within Acrobat. This initial file is just an image, meaning text within it isn’t searchable or selectable.
To optimize this image and enable text recognition, navigate to Tools and select Scan & OCR.
From the dropdown menu within Scan & OCR, choose Enhance Scanned Document. Note that you can also begin with a Camera Image if your document source is a photograph.
Next, click the gear icon to access the settings. In the Enhanced Scanned PDF dialog box, you gain precise control over image settings, allowing you to fine-tune how scanned images are filtered and compressed. While the default settings are generally effective for a wide variety of scanned pages, customization is key for achieving higher image quality, smaller file sizes, or resolving specific scanning imperfections.
Diving into Image Enhancement Settings
Adaptive Compression: Smart Optimization
Activating Apply Adaptive Compression intelligently divides each page into distinct regions: black and white, grayscale, and color. It then applies the most appropriate compression method to each region, preserving visual fidelity while maximizing compression efficiency for each content type.
Compression and Quality Controls
When processing color or grayscale scans, you have the choice of JPEG2000, ZIP, or JPEG compression. It’s important to note that JPEG2000 is not recommended when creating PDF/A files, which are designed for long-term archiving. For black and white or monotone images, select either the lossless or lossy version of JPEG2 or CCITT Group 4. Lossless methods consistently deliver the highest quality. The Quality slider allows you to balance file size and image quality. Moving the slider to the right increases quality and file size, while moving it left reduces file size at the cost of some quality.
Filter Customization for Image Refinement
Click Edit to delve into modifying the filters applied during enhancement.
- Deskew: This automatically corrects any page rotation, ensuring pages are perfectly square, which is generally desirable for scanned documents.
- Background removal: This filter enhances clarity by adjusting the contrast between text and background, making text pop and backgrounds cleaner.
- Descreen: Descreen is designed to remove halftone dot patterns, which can arise from scanning printed materials. Removing these patterns can improve JPEG compression, prevent moiré patterns, and boost text recognition accuracy. If you are scanning pages without images or filled areas, it is advisable to turn Descreen off.
- Text Sharpening: This filter is invaluable when text characters appear to be touching. In such cases, a higher or brighter setting can improve separation. Conversely, if characters are too spaced out, a lower or darker setting might be more suitable.
Text Recognition (OCR) Settings
Select Edit within the Text Recognition section to modify OCR settings. Here, you can specify the document language, which is crucial for accurate text recognition. You also set the PDF Output Style:
- Searchable Image: This option retains the original image and places an invisible layer of text underneath. This allows you to search for and select text within the PDF while preserving the original visual appearance.
- Editable Text and Images: This option converts the PDF into fully editable text and graphics. This is ideal if you need to modify the document content or export it to other formats.
Once you have configured the desired settings, click Enhance to initiate the compression and filtering process. You’ll immediately notice improvements: scans are deskewed, optimized for viewing, and, most importantly, text becomes searchable, layered invisibly over the original image.
Essential Tips for Optimal Scanned Image Enhancement
Keep these key tips in mind to maximize the effectiveness of Acrobat’s Enhance Scans tool:
- Resolution (DPI): Acrobat supports images ranging from 10 dpi to 3000 dpi. For effective text recognition (OCR), a minimum of 72 dpi is required. Input resolutions exceeding 600 dpi will be automatically downsampled to optimize processing.
- Lossless Compression: Remember that lossless compression is exclusively applicable to monochrome images – those containing only a single color or shade.
- Saving Considerations: If you subsequently save the PDF using “Save As,” be aware that the scanned image may undergo further compression, potentially using lossy methods.
- Ideal Scan Settings for Text Recognition: For most documents, scanning in black and white at 300 dpi provides the optimal balance for text recognition. However, if you encounter frequent text recognition errors or are dealing with text smaller than nine points, increasing the scanning resolution is recommended. Always prioritize scanning in black and white whenever possible for text-centric documents.
Scanner-Specific Best Practices
- Avoid Dithering or Halftone: Scanner settings like dithering or halftone, while sometimes enhancing photograph appearance, can significantly hinder text recognition accuracy.
- Colored Paper Adjustments: When scanning text printed on colored paper, try increasing both brightness and contrast by approximately 10% to improve text clarity.
- Color Filtering: If your scanner offers color-filtering capabilities, consider utilizing a filter or lamp that effectively drops out the background color, enhancing text prominence.
- Text Crispness and Dropouts: If the scanned text appears unclear or is dropping out, experiment with adjusting your scanner’s contrast and brightness settings to clarify the scan and ensure crisp text reproduction.
- Manual Brightness Control: If your scanner has manual brightness control, adjust it so that characters are rendered cleanly and well-formed. For touching characters, use a higher or brighter setting; for separated characters, opt for a lower or darker setting.
By leveraging the compression, filter, and text recognition tools within Acrobat’s Enhance Scans feature, you can transform large, difficult-to-read scanned images into optimized, user-friendly documents that are both visually clearer and fully searchable.
