About Threshold (Black & White)

The Threshold tool converts images into pure black and white (binary) images by comparing each pixel's brightness against a threshold value. Pixels brighter than the threshold become white, while darker pixels become black. This creates high-contrast images perfect for document scanning, OCR preparation, artistic effects, and technical applications.

How Threshold Works

The threshold process evaluates each pixel's brightness value (0-255) and makes a binary decision. For example, with a threshold of 128:

• Pixels with brightness ≥ 128 become white (255)
• Pixels with brightness < 128 become black (0)
• No gray values remain - only pure black and white

Calculation Modes

• Luminance (Recommended): Uses weighted formula (0.299R + 0.587G + 0.114B) that matches human eye sensitivity. Green is weighted most heavily as our eyes are most sensitive to green light. Best for most photographs and natural images.
• Simple Average: Calculates (R+G+B)/3 for equal weighting of all color channels. Faster but less perceptually accurate than luminance. Good for images where color channels are equally important.
• Red Channel: Uses only red channel intensity. Useful when red content is most significant, such as highlighting red text or features.
• Green Channel: Uses only green channel intensity. Often produces best contrast in natural photographs due to green's dominance in vegetation and lighting.
• Blue Channel: Uses only blue channel intensity. Can emphasize sky, water, or blue-heavy content.

How to Use

1. Click "Choose Image" to upload your photo or document
2. Adjust the threshold slider (0-255) - start at 128 (middle value) and adjust based on results
3. Select calculation mode - use Luminance for most cases, or experiment with specific channels
4. Click "Apply Threshold" to process the image
5. Compare original and binary versions in the side-by-side preview
6. Fine-tune the threshold value if needed and reapply for better results
7. Download your binary black and white image

Choosing the Right Threshold Value

• Low values (0-85): More pixels become white, less black. Good for dark images or when you want to preserve lighter details.
• Medium values (85-170): Balanced conversion. Default 128 works well for most images with normal contrast.
• High values (170-255): More pixels become black, less white. Good for bright images or emphasizing dark details.
• Tip: If your image is mostly black, lower the threshold. If mostly white, increase it.

Common Use Cases

• Document scanning: Convert photos of documents to clean black text on white background
• OCR preparation: Prepare images for optical character recognition software
• Barcode/QR code enhancement: Improve readability of codes for scanning
• Artistic effects: Create high-contrast graphic art, silhouettes, or poster-style images
• Technical drawings: Convert sketches or blueprints to clean line art
• Stamp/signature extraction: Isolate stamps or signatures from documents
• Pattern recognition: Prepare images for computer vision or machine learning
• Print optimization: Reduce file size and improve printing clarity

Frequently Asked Questions

1. What's the difference between threshold and grayscale?

Grayscale preserves all brightness levels (0-255), showing varying shades of gray. Threshold creates binary images with only two values: pure black (0) and pure white (255). Threshold is more extreme and removes all gray tones, making it ideal for high-contrast applications like document scanning where you need clear separation between text and background.

2. Why does my image look mostly black or mostly white?

Your threshold value needs adjustment. If mostly black, your threshold is too high - lower it so more pixels pass the brightness test and become white. If mostly white, your threshold is too low - raise it so fewer pixels qualify as "bright enough" to become white. Try starting at 128 and adjusting in increments of 20-30 until you get better balance.

3. Which calculation mode should I use?

Use Luminance for 95% of cases as it best matches human vision. Try Simple Average if you want equal treatment of all colors. Use individual color channels when your image has distinct color information you want to emphasize. For example, use Green Channel for vegetation-heavy photos or Red Channel when isolating red-stamped text on documents.

4. Can I use this for scanning handwritten notes?

Yes! Threshold is excellent for handwritten notes. Take a photo of your notes, apply threshold with a value around 140-180 (depending on lighting), and you'll get clean black text on white background. This removes shadows, improves contrast, and makes text more readable. It also significantly reduces file size compared to grayscale photos.

5. How is this different from the Black & White filter?

The Special Filters Black & White creates a grayscale image with smooth tones from black through gray to white. Threshold creates a binary image with only pure black and pure white - no grays at all. Use Black & White filter for artistic photography, use Threshold for documents, technical work, or when you specifically need high-contrast binary output.

6. Why do I see jagged edges in my thresholded image?

Binary images create hard edges because there are no intermediate gray values to smooth transitions. This "aliasing" or "jaggedness" is normal for threshold conversion. It's actually desirable for documents and text as it creates sharp, crisp edges. For smoother results in artistic work, consider using the High Contrast filter instead, which preserves some tonal gradation.

7. Can this tool prepare images for laser engraving?

Yes, threshold is commonly used for laser engraving preparation. Binary images work perfectly with most laser engravers since they operate in on/off mode (burn/don't burn). Experiment with threshold values to get the right amount of detail - typically 110-140 works well for photos, but this depends on your source image and engraver settings.

8. How do I handle images with uneven lighting?

Uneven lighting (like shadows on one side of a document) can make threshold challenging. No single threshold value will work well across the entire image. Pre-process your image first: use the Brightness & Contrast or Exposure tools to even out lighting, or try the Equalize Image tool to balance brightness before applying threshold. Photography tip: ensure even lighting when capturing images you plan to threshold.

9. What threshold value is best for QR codes and barcodes?

For QR codes and barcodes, use values between 120-140. These codes are designed to be binary (black modules on white background), so threshold works perfectly. If your code photo has good lighting and contrast, 128 is ideal. Adjust slightly if the code has shadows or glare. After thresholding, the code should scan reliably with any QR/barcode reader.

10. Can I batch process multiple images with the same threshold?

This single-image tool requires individual processing. For batch processing of documents or multiple images with consistent threshold settings, you'll need to process them one at a time. When processing a series of related images (like pages of a document), find the optimal threshold value for the first image, then use that same value for all subsequent images to ensure consistency.