image tool
Convert image to black and white
Drop a photo and it turns black and white at once, each pixel set to its luminance: how bright it looks to the eye, not a plain average of red, green and blue. A contrast slider then pushes the greys apart or pulls them together before you save a PNG or JPG.
Loading the tool…
- Runs on your device, nothing is uploaded
- Free, no sign in
- No watermark, no file limit
How it works
- 1
Drop the image
The preview turns black and white straight away. Press Show original to flip back to the colour version and compare.
- 2
Set the contrast
Leave the slider at 0 for plain luminance. Move it right for deeper blacks and brighter whites, left for a flatter, softer grey.
- 3
Pick the format
PNG keeps every grey exactly and keeps transparency. JPG is smaller and suits photos. The tool starts on the source format when it is PNG or JPG.
- 4
Download
The full-size image is converted and saved with black-and-white added to its name. Nothing is uploaded and nothing is stored, ever.
Why green comes out lighter than blue
A plain average treats red, green and blue as equally bright, which they are not to the eye. Rec. 709, the standard behind HD video and the sRGB colour space used on the web, weights them at about 21% red, 72% green and 7% blue. So a pure green turns into a light grey and a pure blue into a near black, which is how they actually look. The tool converts each pixel to linear light first, applies those weights, then encodes the grey back to screen values, so mid tones keep the brightness you see in the colour photo.
What the contrast slider does
Contrast is applied after the grey is worked out. At 0 nothing changes. Positive values stretch every grey away from the middle, so shadows get darker and highlights brighter, up to three times the spread at 100. Negative values squeeze them towards a mid grey, down to a flat field at minus 100. A small push, 15 to 30, often helps a colour photo that looks muddy once the colour is gone, because two colours of similar brightness, such as a red jumper on green grass, turn into almost the same grey.
When black and white helps a design
A mono photo sits quietly behind text, so a headline in a strong brand colour reads clearly on top of it. It also hides a mix of photos taken in different light, which is why team pages and event flyers often go grey. And on a print job it saves a colour that would otherwise clash with the paper or the ink. If the design has one accent colour, keeping every photo grey lets that colour do all the work.
Limits worth knowing
The conversion uses Rec. 709 luminance, not a print dot gain curve. Ink spreads into paper, so a printed grey is darker than the same value on screen, and a photo with lots of shadow detail can close up in print. Check a proof on the paper you will use before printing hundreds. The tool opens images up to 8,192 pixels on the long side and refuses bigger ones with a plain message rather than freezing the tab. Re-encoding drops the EXIF block, so keep the original if you need the date it was taken.
Using the photo on a flyer
The flyer builder takes JPEG, PNG, WebP and GIF uploads up to 10 MB, and an image slot fills its frame, cropping whatever does not fit. Its text style controls include a custom hex colour per text slot, so a grey photo with one coloured headline is a few clicks once the image is converted here.
Limits
- It uses Rec. 709 luminance, not a print dot gain curve. Greys that look right on screen can print darker, so check a proof on paper before a long run.
- The file still has three colour channels holding the same value. It is grey in every way that shows, but it is not a single channel grayscale file.
- Images larger than 8,192 pixels on the long side are refused with a message.
- Saving as JPG fills transparent areas with white and compresses at quality 92.
What it does not do
- It does not convert to CMYK or add a colour profile for a printer.
- It does not tone the image sepia or with any other colour; the result is neutral grey.
- It does not keep EXIF data. The camera, date and location tags are not copied to the new file.
Questions people ask
Is black and white the same as greyscale?
In everyday use, yes: both mean a photo made only of greys. Strictly, black and white can also mean pure black and pure white with no greys at all, which is called a threshold or bitmap image. This tool makes the greyscale kind, with up to 256 shades between black and white, which is what people expect from a black and white photo.
Why does my black and white photo look flat?
Colours that stood apart in the original can have almost the same brightness, so they become the same grey. A red sign on green leaves is the classic case. Move the contrast slider right, 15 to 30 is a good start, to separate them. If two areas still merge, the photo needed colour to tell them apart and may suit a different crop.
Will it print in grey on a colour printer?
Usually, but not always neutral. Many colour printers build grey from cyan, magenta and yellow ink, which can drift warm or cool. The file holds equal red, green and blue values, so the colour is neutral in the data. For the most neutral print, choose the printer's greyscale or black ink only option in the print dialog.
Can I convert a transparent logo to grey?
Yes. Keep PNG as the format and the transparent background stays transparent, with only the visible parts turned grey. If you save as JPG instead, the transparent areas are filled with white, because JPG has no alpha channel. The checkered pattern behind the preview shows which parts of the image are transparent.
Does the tool make the file smaller?
Sometimes, but not by much. The output still stores three colour channels, so a JPG of the grey version is usually close to the size of the colour one. Grey photos do compress a little better because the channels match. If you need a much smaller file, run the result through the image compressor or reduce its pixel size.
Put a mono photo on a print flyer
Take what you made here into flyers.
Create a flyer with OneCraftMore tools like this
- Invert image coloursInvert image colours online: every red, green and blue value is flipped, transparency kept, saved as PNG. Made for icons and line art. Nothing is uploaded.
- Image colour changerTap a colour in the image, pick its replacement, and see a mask of exactly which pixels change. Runs on your device, so the artwork is never uploaded.
- Contrast checkerSet a text colour and a background and read the WCAG ratio on a live specimen, with a pass or fail attached to every size from 30px down to 13px.
- Image compressorCompress to WebP or JPEG and compare the result against the original under a divider you drag. Or ask for a size in KB. Nothing is uploaded.
- Convert an imageSee your own picture measured in PNG, JPEG and WebP before you choose, then convert. Transparency is handled deliberately, and HEIC is explained.
- Rotate image onlineRotate an image online by 90, 180 or 270 degrees, or flip it horizontally or vertically, and save it in the same format. Runs on your device, nothing uploaded.
Background reading: the question page on this.
Written and checked by the OneCraft team. Last checked .