Grayscale Image Converter

The Grayscale Image Converter strips all colour from a picture and saves it as a greyscale JPG with the same pixel dimensions. Use it for a classic black-and-white look, to preview how something will print on a mono printer, or to check whether a chart or poster still makes sense without colour.

How colours turn into shades of grey

The tool applies the browser's standard grayscale filter, defined in the CSS Filter Effects specification. Instead of simply averaging red, green and blue, it weights them the way human vision does:

grey = 0.2126 × red + 0.7152 × green + 0.0722 × blue

These are the Rec. 709 luminance weights. Our eyes are far more sensitive to green than to blue, so a vivid green becomes a light grey, a vivid red a darker grey, and a pure blue very dark. A plain average would turn all three into the same flat grey, which is why photos converted this way keep more natural contrast.

Converting a picture

1. Drop a JPG, PNG, WEBP or iPhone HEIC photo onto the upload box; HEIC files are decoded first.
2. Click Process image. The Result preview appears next to the original with its dimensions and file size.
3. Click Download result to save the JPG.

The file is saved at a fixed JPEG quality of 92%, so the Quality slider shown on the page does not affect this conversion.

Watch out for transparent backgrounds

JPG has no transparency. Under the HTML canvas standard, transparent pixels are placed on an opaque black background when saving to a format without alpha, so a logo with a transparent background comes out on solid black. If you want white instead, first run the PNG through PNG to JPG, which fills transparency with white, and then convert that JPG to greyscale.

Practical uses

• Printing previews. Before sending a brochure or report to a mono laser printer or photocopier, see which elements merge into the same grey.
• Checking charts and maps. Red and green lines of similar brightness become nearly identical greys. If your chart only works in colour, add labels, patterns or line styles; this also helps colour-blind readers. For text, confirm legibility with the colour contrast checker.
• Document photos. A photographed page under yellow indoor light looks cleaner without the colour cast, and some forms ask for a black-and-white copy.
• Photography. Portraits, textures, architecture and scenes with strong light and shadow often look striking in monochrome.

Limits to know before you convert

• The conversion cannot be reversed; colour information is discarded. Keep your original file.
• Contrast is not boosted. A flat, hazy photo stays flat in grey; the best results come from images with a clear range of light and dark.
• "Grayscale" means up to 256 shades of grey, not pure black-and-white line art, and there are no sepia or tint options.
• Camera metadata is not copied into the new file. The picture is processed in your browser and is never uploaded.