Inverting your film negative

Your negative, converted the way film records light. The conversion works in density, so your highlights keep their room and your photo edits like a print.

From your negative to your photo, in three steps.

Open your negatives, say what the film is, edit. Density inversion is not an option to find: every conversion goes through it.

Open your negatives. Choose Open Folder… in the File menu (⌘O, or Ctrl+O on Windows) on the folder of one film.
NegativePositiveB&W
Say what your film is. Negative, Positive or B&W, in the first step of Prepare the Roll or later in the Roll tab.
Exposure+0.00 EV
Edit your photo. Exposure reads in EV: a full stop in the shadows, while the highlights roll toward white instead of clipping.

Every stop of your scene gets the same room.

The conversion works in density. A plain invert leaves a cyan cast and squashes your highlights. Film records light in stops, so your negative is converted in stops: the sky stays above the ground and every tone keeps its room.

Read the research

The model gliders photograph inverted value for value: a cyan cast over the grass and the glider, under a dark teal sky. — **A plain invert.** Your scan flipped value for value: a cyan cast over everything, and a sky darker than the ground.

The same photograph converted in Open Negative Initiative: a blue sky over golden grass and an orange glider. — **Converted in Open Negative Initiative.** The same scan, inverted in density: the sky back above the ground.

Ten stops of one scene on an illustrative film

Stop	In the scan	After a plain invert	Density
1	0.631	0.369	0.20
2	0.416	0.584	0.38
3	0.275	0.725	0.56
4	0.181	0.819	0.74
5	0.120	0.880	0.92
6	0.079	0.921	1.10
7	0.052	0.948	1.28
8	0.034	0.966	1.46
9	0.023	0.977	1.64
10	0.015	0.985	1.83

Ten stops of one scene, two ways. In the scan, the highlights, dense on the negative, crowd near zero, and a plain invert keeps the crowd at the other end: the brightest five stops share 6 % of the scale. In density, every stop is the same distance apart. A diagram of the principle, on an illustrative film.

What it changes when you edit your photo.

Exposure works like a print exposure. Exposure, and the Source Balance of the Roll tab, both read in EV.

Exposure+0.00 EV
Exposure, in stops. It reads in EV and starts at zero. A stop is a full stop in the shadows; the highlights roll toward white instead of clipping.
Cyan ↔ Red+1.00 EV
Colour balance, in stops too. Source Balance, in the Roll tab, pushes each channel of your negative in EV: a colour negative's three channels never start from the same point.

Density inversion: questions

Inversion, cyan casts and slide film. The short answers first, then the detail.

Why not simply invert a negative with 1 − x?

Because a scan is linear: the dense areas of the negative, which are the highlights of the scene, arrive as very small numbers, crowded into the first few percent of the range. Subtracting them from one keeps the crowd, at the other end, and every control then works on a badly stretched axis.

Do I have to turn density inversion on?

No. The whole chain already works in density. The film type you set for the roll only changes the sign of one step, for a slide.

Does it work for slide film?

Yes. Slide film is Positive, the film type you set for the roll in the first step of Prepare the Roll or in the Roll tab, and it is the one case where a sign is flipped, because a slide was already a positive picture before it was scanned. Black and white has its own type beside it, B&W.

Can a channel that hit the scanner's black level be recovered?

No. A channel clipped at the scanner's black level arrives at nothing at all, or a hair below it as sensor noise, and no setting recovers it.

What happens at zero

The logarithm has no answer at zero, and a scan holds zeros for two reasons: a channel clipped at the scanner's black level, and an area brighter than the film base, which is a negative density and a perfectly healthy reading.

So every value is lifted by a small constant, the pedestal, set by the Density Ceiling, and the small ones keep their differences instead of being clamped to one floor. A numerical guard an eighth of the pedestal lower catches the rest.

A track graduated in density

The levels track runs from −0.35 to 3.0 in density, the film's own unit, so a number on a handle reads like a number on a datasheet. A black point can sit under zero, where a channel transmitting more light than the film base lands, so the track keeps room below the bare film for a reading that is perfectly healthy.

What do converted frames look like?

See all sixteen conversions, real photographs converted in Open Negative Initiative, each with its raw scan.

The rest of the conversion.

From your scan to your export. One page per feature.

Convert your first roll tonight.

Add your folder, prepare the roll once, export. Free, and nothing else to install.

Download for MacDownload for Windows

How to convert a film negative, step by step

Mac: macOS 13 or later on Apple Silicon or Intel
Windows: Windows 10 or 11 (64-bit)

Blocked at first launch?

A snowy Paris street at night, a lit cafe under arcades, tyre tracks in the snow. — **Snow night.** Kodak Gold, converted in Open Negative Initiative.

The research.

Film is measured in density. What your scan holds, why a colour negative is orange, and what that means for your shadows, your highlights and your colour.

Density	Light through	Stops held back
0.1	79 %	0.3
0.3	50 %	1
0.6	25 %	2
1.0	10 %	3.3
2.0	1 %	6.6
3.0	0.1 %	10

Density, step by step. Every 0.3 of density holds back about one more stop of light. A deep shadow, barely exposed, sits near 0.1 and lets 79 % of the light through; a white sky, exposed hard, reaches 2.0 and lets through 1 %.

What density is

Density is how much light a piece of film blocks. 1.0 lets a tenth of the light through, 2.0 a hundredth, 3.0 a thousandth: D = −log₁₀(T), where T is the transmittance, the fraction of the light that gets through.

Film has been measured this way since its first datasheets, because density follows exposure the way your eye follows light: doubling the light always moves density by about 0.301. On that scale a stop is the same distance in the deepest shadow and in the brightest highlight, and that is the scale your negative is converted on.

The mask is one density per channel. Density per channel, on an illustrative film: the mask (in grey) sits under every tone of the frame, densest in blue. Measured at the BASE step, it comes off each channel, and a grey of the scene stands at the same 0.5 in all three.

Why your colour negative is orange

The orange mask is there on purpose. The magenta and cyan dyes of a colour film absorb a little of the light they should pass, so the film carries coloured couplers that compensate for it, and they leave the whole negative orange. A printing lab balanced it out with filters; a scan keeps all of it.

The couplers are used up where dye forms, so the mask and the dyes' stray absorption add up to an even density across the frame: in density, one constant per channel, which comes off by measuring the bare film. Pick it at the BASE step of Prepare the Roll, the border or the gap between two frames, and it becomes each channel's black: the scene's own zero.

One grey, two inversions. The value each channel ends with, for the same grey through the same illustrative mask. Subtracted from one, red falls behind green and blue, and the grey turns cyan. Inverted in density, the three channels read alike.

Where the cyan cast comes from

Flip an orange negative value for value and the orange becomes its complement: a blue-cyan veil over the whole frame. It is the same in every photo editor, because the mask is a density and subtraction treats it as a colour.

Taken off in density, the mask goes the way it went on, channel by channel, and the three channels then share one black. The roll's measurement finishes the job: it reads every frame and brings red and blue onto green, as an enlarger's colour head did with its filters.

How a film answers light. An illustrative colour negative curve: below the meter reading the tones flatten onto the bare film; above it, density keeps climbing for stops, where an overexposed frame keeps its highlights.

Thin and dense negatives

An underexposed negative is thin: the shadows of your scene sit almost on the bare film, with little density to tell them apart. An overexposed one is dense: the highlights pile up where the film blocks the most light, and colour negative film holds a lot of overexposure there, which is why photographers rate it generously.

Both convert on the same scale. A thin frame keeps the difference that made it thin, and the Lighting block of the Color tab lifts it like a print given more light. A dense frame keeps its highlights, and the Density Ceiling of the Roll tab reveals more detail in its densest parts.

How the Density Ceiling reads your scan. The app's own reading, D = −log₁₀(x + 10^−ceiling), at three of its settings. The higher the ceiling, the further the darkest values of your scan, the densest parts of the negative, stay apart before they level off.

More detail in a dense negative

The Density Ceiling, in the Roll tab, sets how deep into your negative the conversion reads: 2.097 by default on a scanner file, the floor of its range, which runs to 2.6, and 3.5 on a camera RAW negative, whose range runs to 4. A slide, already a positive, works without one.

Raise it on a dense negative and the app reveals more detail in the densest parts, the brightest areas of your scene, with the grain and noise of those areas more visible too. It is the roll's setting, so one move reaches every frame measured with it.

The same negative, scanned twice. Ten tones of an illustrative film on a scanner whose black level sits at 1 % of its light. Exposed for the bare film, the ten stay apart; three stops darker, the four densest arrive as one value.

Scanning so every density survives

On a scan, the bare film is the brightest thing in the frame and the highlights of your scene are the darkest. So expose the scan for the bare film: as bright as it goes while the film base stays clear of white, which lifts the densest parts well above the scanner's black level.

A channel that reaches the black level arrives as one flat value, and a frame scanned a little brighter brings that detail back. With a camera scan, shoot the whole roll in manual, at one shutter speed, aperture and ISO, so every frame starts from the same light.

Five points per channel. Illustrative positions on the levels track, which runs from −0.35 to 3.0 in density, the film's own unit: three channels, each with its own black and white.

The per-channel levels

A colour negative's three channels never start from the same point, so each gets its own black and white. The per-channel levels live in the Roll tab, and the roll's measurement places them for every frame.

Each channel carries five points: black, shadows, midtone, highlights and white. Above them, Source Balance pushes each channel in EV, on three tracks: Cyan ↔ Red, Magenta ↔ Green and Yellow ↔ Blue.

Light	What daylight film records	In Source Balance
Daylight	The colours of the scene	Every track at zero
Tungsten bulbs	A warm, orange scene	Yellow ↔ Blue toward Blue, Cyan ↔ Red toward Cyan
Fluorescent tubes	A green scene	Magenta ↔ Green toward Magenta

Casts on daylight film, and the track that answers each. Source Balance, in the Roll tab, corrects the roll once; Auto White Balance then sets each frame's own light.

A colour cast, corrected in stops

Most colour negative film is balanced for daylight. Shot under tungsten bulbs it records a warm, orange scene; under fluorescent tubes, a green one. In the darkroom the printer dialled filters on the enlarger's colour head, each a fraction of a stop of one colour, and the cast went away while the greys stayed grey.

Source Balance works the same way: each track pushes one channel of your negative in EV, so a stop of red is the same correction in the shadows and in the highlights. Fix the roll's cast once there, then give each frame its own light with Auto White Balance in the Color tab.

Film type	Your film	Orange mask	The conversion
Negative	Colour negative film	Yes, measured at the BASE step	Inverted in density, the mask taken off channel by channel
Positive	Slide film, already a positive	No	Kept positive, balanced on a white or grey you click
B&W	Black and white negative film, in silver	No	Inverted in density, like a colour negative

Three film types, one choice per roll. Set in the first step of Prepare the Roll, or later in the Roll tab.

Slides and black and white

A slide was already a positive picture before you scanned it, so Positive is the one film type that flips a sign. Prepare the Roll balances a roll of slides on a white or grey you click on one slide, its colour alone, and leaves each slide's black and white as you shot them; without a click, your slides keep the camera's 5500 K.

Traditional black and white film is silver, with no orange mask, and B&W is its own film type beside Negative and Positive. Choose the film type once for the roll, in the first step of Prepare the Roll or in the Roll tab: the wrong one converts every frame of the roll wrong.