Image Threshold

What is thresholding?

Thresholding is the simplest method of converting a grayscale image into a binary (black and white) image. Every pixel whose brightness exceeds a chosen threshold value becomes white, and every pixel at or below the threshold becomes black. The result is a high-contrast, two-tone image that strips away all tonal information and keeps only the structural outline. Thresholding is a fundamental operation in image processing, used for segmentation, document scanning, edge detection and artistic effects.

This tool runs entirely in your browser. When you upload an image, it is decoded through the Canvas API. As you drag the threshold slider, the tool converts each pixel to grayscale using the standard luminance weighting, compares it to the threshold, and sets the pixel to pure black or pure white. The preview updates instantly, and the result can be downloaded as a PNG file. Nothing is ever uploaded to a server.

Binary images

A binary image contains only two pixel values: 0 (black) and 255 (white). This is the most compact representation of an image's structure — every pixel is either on or off. Binary images are used in optical character recognition (OCR), document analysis, fingerprint analysis, and any application where the exact tonal values are less important than the shapes and boundaries they define. Because each pixel needs only 1 bit of storage, binary images also compress extremely well.

When to use thresholding

Thresholding is useful whenever you need to separate foreground from background or create a stark, high-contrast image. Common use cases include:

Otsu vs manual threshold

Thresholding is useful whenever you need to separate foreground from background or create a stark, high-contrast image. Common use cases include:

• Document scanning. Convert a photographed document into a clean, high-contrast black-and-white scan suitable for OCR or printing.
• Line art extraction. Separate pencil or ink lines from paper background in scanned drawings.
• Silhouette creation. Turn a subject into a solid black silhouette against a white background.
• Stencil and screen-print preparation. Reduce an image to two tones for cutting stencils or making screen-print separations.
• Image segmentation. Separate objects from their background as a first step in analysis or compositing.

Whenever you need a clean, two-tone image that preserves only the structural information, thresholding is the fastest and simplest approach.

How to threshold an image

Thresholding an image with this tool takes only a few seconds and runs entirely in your browser — no uploads, no sign-up, no watermark. Follow these steps:

1. Upload your image. Click the upload area or drag and drop a JPG, PNG, WebP, GIF or BMP file.
2. Adjust the threshold. Drag the slider from 0 to 255. A lower threshold makes more of the image white, while a higher threshold makes more of it black. The preview updates in real time.
3. Download the result. Click "Download Threshold Image" to save the binary PNG.

Because every step runs locally through JavaScript, your image is never sent to a server. This makes the tool completely private and fast.