What is the difference between greyscale and black & white?

Greyscale keeps many shades of grey based on each pixel's brightness. Pure black & white forces every pixel to either fully black or fully white using a threshold, giving a high-contrast 1-bit look.

How is greyscale brightness calculated?

It uses the perceptual luminance formula 0.299R + 0.587G + 0.114B (ITU-R BT.601), which matches how the human eye weights red, green, and blue.

What does the threshold slider control?

In black & white mode the threshold (default 128, range 0-255) is the brightness cutoff. Pixels brighter than the threshold become white and the rest become black, so a lower threshold keeps more white and a higher one makes the image darker.

When should I use black & white instead of greyscale?

Use 1-bit black & white for high-contrast art, scanning line drawings, logos, or preparing images for risograph or laser engraving where only pure black and white print. Use greyscale when you want to keep tonal detail.

Does it keep transparency?

Yes. Only the red, green and blue channels are recomputed; the alpha channel is preserved, so transparent PNGs stay transparent.

Is my image uploaded anywhere?

No. The conversion happens entirely in your browser using the canvas API, so your photo never leaves your device.

What is the Image to Grayscale / Black & White?

Free grayscale and black & white image converter. Turn any photo into perceptual greyscale shades or a pure black-and-white image with an adjustable threshold. Runs entirely in your browser — no upload. It runs free in your browser on Gera Tools, with nothing uploaded.

Image to Grayscale / Black & White

Name: Image to Grayscale / Black & White
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Grayscale and black and white image converter

Convert any photo to perceptual greyscale or a pure 1-bit black and white image. Greyscale keeps the full range of grey tones, while black and white mode forces every pixel to either black or white for a crisp, high-contrast result — ideal for line art, scans, logos, stencil-style output, and risograph print preparation.

How it works

The image is read into a <canvas> and every pixel is converted to a brightness value using the perceptual luminance formula:

lum = 0.299R + 0.587G + 0.114B (ITU-R BT.601)

Greyscale: each pixel’s red, green and blue are all set to lum, keeping the full 0-255 range of shades.
Black and white: the luminance is compared against a threshold (default 128). If lum ≥ threshold the pixel becomes white (255), otherwise it becomes black (0).

Worked example

A pixel with R=200, G=180, B=120 gives lum = 0.299×200 + 0.587×180 + 0.114×120 ≈ 179.

Mode	Threshold	Output pixel
Greyscale	—	grey 179
Black and white	128	white (179 ≥ 128)
Black and white	200	black (179 < 200)

Understanding the threshold slider

The threshold controls how “dark” a pixel must be before it prints as black. The default of 128 is the mathematical midpoint (halfway between 0 and 255).

Lower threshold (closer to 0): only very dark pixels become black; most of the image becomes white. Good for images with dark line art on a light background where you want to preserve fine thin lines.
Higher threshold (closer to 255): more pixels become black. Good for capturing mid-tone detail in a photo-realistic source image, or for printing where the paper absorbs ink and dark areas need to dominate.
Extreme thresholds (below 30 or above 220): most pixels will be one colour; useful for silhouette effects.

Greyscale vs. black and white: choosing the right mode

Greyscale is best when tonal nuance matters: portrait photography, technical diagrams, print layouts where you want continuous shading, accessibility reviews where you check colour-independence of UI designs.

Pure black and white is best when the output goes to a process that can only handle two values: laser engravers, pen plotters, risograph printers, two-colour screen printing, stencil cutting, and certain OCR pre-processing workflows that need maximum contrast.

The ITU-R BT.601 luminance formula is the standard used by video and broadcast systems. It weights green at 58.7%, red at 29.9%, and blue at only 11.4%, reflecting the eye’s greater sensitivity to mid-range green wavelengths. This makes greens appear natural and prevents blues from looking unexpectedly bright in the output.

Everything runs in your browser — your image is never uploaded. The output downloads as a lossless PNG.