Are my images uploaded?

No. Pixels are read and rewritten with the canvas getImageData / putImageData API in your browser. The image never leaves your device.

How accurate are the colours?

The default uses the ITU-R BT.601 luminance formula (0.299R + 0.587G + 0.114B), which matches how the eye perceives brightness and is the standard for greyscale conversion. A simple-average option is also provided.

What is the difference between the two greyscale modes?

Perceptual luminance weights green most and blue least, giving natural-looking results. The simple average treats all channels equally, which can look flatter but is faster to reason about.

What does the sepia option do?

Sepia applies the classic warm reddish-brown tone of old photographs by mixing the channels with the standard sepia matrix instead of fully desaturating, giving a vintage look rather than neutral grey.

Will greyscale reduce file size?

The PNG is still saved in colour mode, so the file may not shrink much. Greyscale removes colour information visually but the canvas still writes three colour channels plus alpha.

Does this keep transparency?

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

Image to Grayscale — Gera Tools

Convert images to grayscale or sepia, privately

Turn any photo black and white, or apply a warm sepia tone. This is useful for print layouts, accessibility mock-ups, vintage effects, or simply reducing visual noise — and it all runs locally so your photos never leave your device.

How it works

The image is loaded into a <canvas> and read with getImageData. For each pixel the chosen formula computes a new value:

Perceptual greyscale (default): 0.299R + 0.587G + 0.114B (ITU-R BT.601 luminance), which matches how the human eye weights brightness — green contributes most, blue least.
Simple average: (R + G + B) / 3, treating all channels equally.
Sepia: the standard sepia matrix is applied for a warm tone.

The recomputed pixels are written back with putImageData and exported as a lossless PNG.

Example

A mid-blue pixel with R=40, G=90, B=200:

Perceptual: 0.299×40 + 0.587×90 + 0.114×200 = 87 (a dark grey)
Simple average: (40 + 90 + 200) / 3 = 110 (noticeably lighter)

The perceptual result looks more natural because blue is perceived as darker than its raw value suggests.

Every pixel is processed with a <canvas> on your device — your image is never uploaded — and the result downloads as a lossless PNG.