Four kinds of “invert”
| You have | Choose | What happens |
|---|---|---|
| Any picture, for a negative or X-ray look | All colours | Every value v becomes 255 − v. Black ↔ white, red ↔ cyan, blue ↔ yellow |
| A screenshot, diagram, drawing or logo that should work on a dark background | Light and dark only | Lightness flips, colours keep their hue: a red mark stays red |
| A phone photo or scan of colour negative film | Colour film negative | The orange film base is measured and divided out, then the film is turned into a positive |
| A photo or scan of black-and-white film | Black-and-white film negative | The film’s density range is measured and spread from black to white |
Why an inverted colour negative turns blue
Colour negative film is orange even where nothing was exposed. That orange base, the “mask”, is part of how the film reproduces colour, and every frame sits on top of it. A plain invert turns the orange into its opposite, dark blue, and pushes the whole photo towards blue. We modelled a typical scan (an orange base of RGB 222, 148, 100 and the usual contrast of colour negative film) and inverted it:
| Part of the picture | Plain invert | Colour film negative mode |
|---|---|---|
| Clear film edge (should be black) | RGB 33, 107, 155 — dark blue | RGB 16, 16, 16 |
| Mid grey in the scene (L* 50) | L* 80, b* −12.8 — pale and blue | L* 49.6, b* 1.6 |
| White in the scene | L* 88, b* −8.6 | L* 96.6, b* 0.1 |
Two things go wrong with a plain invert, not one: the blue cast, and the tones. Film stores light as density, on a logarithmic scale, so simply flipping the numbers squashes the photo into a pale, low-contrast picture. On a whole landscape photo turned into a modelled negative, the plain invert was off from the real photo by an average colour difference of 31; this page’s colour negative mode by 9.
How the film modes work
The page finds the clearest film in your scan, the brightest 0.2% of each colour, and takes it as the base. Each colour is divided by its base, which removes the orange, and turned into density. The density range of each colour is then measured and spread over about seven stops, from black to white. Because all three colours are stretched between the same two ends, something grey on the film comes out grey. The result note shows the base colour it found.
Two tips for photographing negatives with a phone: put the film on an even light source, such as a tablet showing a white page, and keep a little of the clear film edge in the frame. Pure white areas such as the light table around the film are left out of the measurement automatically, but cropping them away is still cleaner. Different film brands have different bases, and each frame is measured on its own, so a roll of mixed film works too.
Light and dark only: a dark-mode invert
A classic invert turns a red logo cyan and a blue link orange. For a screenshot or a chart that needs a dark version, that is rarely what you want. This mode flips lightness in the OKLab colour space and keeps the colour itself: on our red and green test pattern the hue of the coloured pixels moved by 1 degree on average. Some colours cannot exist at their new lightness (a dark yellow is brown), so those are made slightly less saturated and the note tells you how many.
Transparency stays exact
Inverting a PNG logo should not change its outline. Browsers read semi-transparent pixels through a canvas that rounds their colours, so this page reads PNG files itself. On our test logo all 4,336 semi-transparent edge pixels kept exactly their transparency, and every visible pixel came out as precisely 255 minus its value. Save as PNG to keep it.
Related tools
To fine-tune a converted negative, brighten it or make it black and white. To straighten a crooked scan, use Rotate image, and to cut away the film holder, Crop image. To make a logo’s white background see-through after inverting, use Make background transparent.