How to Convert a Photo to Black and White
Taking the colour out of a photograph is one click. Getting a black and white photograph that looks intentional is a different matter, because once colour is gone the only thing left carrying the image is contrast. The Grayscale Image Converter does the conversion properly using luminance weighting.
Why the maths matters
The obvious way to remove colour is to average the red, green and blue channels. It is also wrong, because the eye does not weigh those channels equally - green reads as much brighter than blue at the same numeric value. Averaging turns a vivid red and a deep blue into the same mid grey, and the picture goes flat.
Proper conversion uses luminance weighting: roughly thirty per cent of the red, fifty-nine per cent of the green and eleven per cent of the blue. That matches how human vision responds, so tones that looked different in colour still look different in grey. It is the difference between a photograph and a photocopy.
Which pictures suit it
Black and white rewards strong shapes, texture and a clear difference between light and dark. Architecture, faces in directional light, weather, anything with a strong silhouette. It also rescues a photograph taken under mixed lighting, where one side is orange from a lamp and the other blue from a window - a colour cast nobody can fix becomes irrelevant the moment colour goes.
It does not suit a picture whose whole point was the colour. A sunset, a market stall, a painted door: strip the colour and there is nothing left to look at. The test is simple - squint at the photograph until you cannot make out the detail. If the shapes still read, it will work in grey.
Fix the exposure first
A flat, underexposed photograph becomes a flat grey one. Brightness and contrast are worth adjusting before the conversion rather than after, and the Image Editor handles both. A conversion is also a good moment to crop, since black and white is less forgiving of clutter at the edges.
Common questions
Does converting to black and white make the file smaller?
A little, since there is less colour information to store, but not dramatically - the file still holds a full tonal range. For a real reduction use the Bulk Image Compressor.
Can I get the colour back afterwards?
Only from your original. The conversion discards the colour information permanently, so keep the colour version.
Is grayscale the same as black and white?
In everyday use, yes. Strictly, grayscale has the full range of greys while true black and white has only two tones, which is what a fax or a line drawing uses.
Why does my converted photo look muddy?
Usually low contrast in the original, which the conversion then has nothing to work with. Lift the contrast before converting and the tones separate.
Should I convert before or after cropping?
Crop first. Black and white draws the eye straight to shape, so anything untidy at the edges of the frame becomes more obvious rather than less.
Ready to see a photograph without its colour?