Convert a negative photo

This site reverses pictures: left for right, top for bottom. Inverting colour is the same kind of operation in a different direction — light for dark — and it shares the property that matters most here. Do it twice and you are back where you started, exactly. So the plain negative is written the same way the flips are: each red, green and blue value becomes 255 minus itself, transparency is left alone, and the result can be checked by inverting it again and comparing every value with the source.

Film is different. A colour negative is not just an inverted photo; its base is dyed orange so the colours print correctly on paper, and inverting that base gives the familiar blue cast. Film mode samples the base colour from the brightest part of the border (or from a point you pick), divides each channel by it to cancel the mask, inverts, and then stretches each channel from its 0.1 % to 99.9 % values. That is an approximation and it is labelled as one.

1. 1Open the picture. A photo to turn into a negative, or a phone photo or scan of a film negative to turn positive.
2. 2Choose the kind. Plain negative inverts every colour exactly. Brightness only inverts light and dark but keeps hues roughly where they were. Film negative removes the orange mask of colour film before inverting.
3. 3Adjust. For film, the base colour is sampled from the border automatically; pick a clear strip of film by hand if colours look off. Tick "also flip" if the negative was scanned from the wrong side.
4. 4Save and check. A plain negative saved as PNG can be checked: inverting it again gives back the original, value for value.

A 2400 × 1600 PNG inverted with the plain negative becomes a 2400 × 1600 PNG in which a pixel of (200, 120, 40) is (55, 135, 215) and its transparency is unchanged. Inverting the saved file again and comparing gives 0 differences in 15,360,000 channel values. A phone photo of a colour negative whose film base measures about (230, 150, 100) is divided by that colour before inverting, so the clear base becomes black and the orange cast drops out; the levels stretch then spreads each channel across the full range.

• Film mode is a starting point. Each film stock and scanner needs its own correction. The positive will usually need colour adjustment elsewhere.
• Only plain inversion is exact. Brightness-only, the levels stretch and film mode change values in ways that cannot be undone exactly.
• No dust or scratch removal. Cleaning up a scan is retouching, not reversal, and it is not offered.

Why is my colour negative blue after inverting?

Colour negative film has an orange mask built into its base. Inverting orange gives blue, so a plain inversion of a colour negative comes out with a strong blue cast. The film mode divides out the base colour first — sampled from an unexposed strip — then inverts and stretches each channel, which removes most of it.

Is inverting reversible?

Plain inversion is: each value becomes 255 minus itself, transparency is untouched, and doing it twice gives back the original exactly — the Check proves it on your picture. Brightness-only inversion, the levels stretch and film mode are approximations and have no exact inverse.

Can I flip and invert at once?

Yes. A negative or slide scanned from the wrong side needs a horizontal flip as well; tick "Also flip left to right" and both happen in one save.

Will this match a lab scan?

No, and the page says so. Every film stock needs its own correction; film mode gives a positive that is a starting point for colour work, not a finished print.

What about black-and-white negatives?

Use plain negative with "stretch the levels" on. A black-and-white negative has no orange mask, so it only needs inverting and its contrast opening up.