Convert an Image to Pure Black and White With a Threshold
Force every pixel to either solid black or solid white, with a slider deciding where the cut falls.
About the Black & White Image Converter
This is not the same operation as removing colour. Grayscale keeps a full range of intermediate tones; this tool keeps exactly two. Every pixel's perceived brightness is measured, compared against a threshold you control, and then written as either pure black or pure white with nothing in between. The threshold slider spans the full 0 to 255 range and sits at 128 by default, which is the midpoint.
Moving that slider is the whole craft of using this tool. Raise it and more of the image falls below the line and turns black; lower it and more survives as white. On a faded scan, a few points either way is the difference between text that reads cleanly and a page that has dissolved into blotches, so the live preview is doing real work here. Because the conversion runs locally, documents that should not be circulated can be cleaned up without leaving the machine.
Key Features
- Adjustable cut-off point: The threshold runs across the whole 0 to 255 brightness range so you can tune it to the specific image.
- Two tones only: Output contains solid black and solid white with no intermediate greys at all.
- Live threshold preview: The image redraws as the slider moves, which is essential for finding the value that makes faint text legible.
- Transparency untouched: Only the colour channels are rewritten, so an alpha channel in a PNG passes through intact.
- Batch processing: Run a stack of scans through under one threshold setting.
How to Use the Black & White Image Converter
- Add the image or scan you want to reduce to two tones.
- Drag the threshold slider and watch the preview — lower values keep more white, higher values push more to black.
- Settle on the value where the detail you care about is clearest.
- Choose an output format and convert.
How It Works
Each pixel's brightness is calculated in script from the red, green and blue values using the standard perceptual coefficients of 0.299, 0.587 and 0.114, then compared against your threshold and replaced with 0 or 255 across all three channels. Two limits follow from that being a single global comparison. There is no dithering, so a smooth gradient does not become a pattern of dots — it becomes a hard band. And the threshold is one number applied to the entire image, so a scan that is brighter on one side than the other cannot be corrected in a single pass; even out the lighting with the brightness and contrast tool first, then threshold the result.
When You Need It
An archivist digitising decades of paper personnel records finds the scans come out grey and washed out, with typed text barely separable from the paper. Thresholding hardens the letters into solid black on clean white, which both makes them readable and gives character recognition software a far better chance. Those files contain named individuals and employment history, so the cleanup has to happen on equipment the organisation controls rather than through a public image service. Makers preparing artwork for vinyl cutting or laser engraving threshold their files for the same two-tone output, driven by the machine rather than by legibility.