A converter for colour, black and white and slide film
One converter for three kinds of film. Pick the type, set the levels per channel and save the positive as a PNG or a JPG.
How to use the negative to positive converter
- Pick the film type before anything else, because it changes the formula: Colour negative, Black and white or Slide.
- Drop in the scan. For a colour negative, sample the film base; the other two types skip that step.
- Read the levels per channel under the film type. They show the black and white point of red, green and blue.
- Use Temperature and Tint for a cast that is left. The table on this page lists what each setting multiplies.
- Choose PNG or JPG and press Download positive. This page starts on PNG.
Three film types, three formulas
A converter hides its formula, so I wrote mine down and checked each line by hand. Black and white is the plain inverse: a pixel of 200 becomes 55. With levels from 0.1 to 0.9 the same pixel becomes 37, because (0.2157 − 0.1) ÷ 0.8 is 0.1446 of 255.
Slide skips the inversion. A pixel of 100 with levels from 0.2 to 0.8 becomes 82. Only colour negative needs the base, and I list the gains of its two colour sliders below.
What Temperature and Tint multiply
| Setting | Red | Green | Blue |
|---|---|---|---|
| Temperature −100 | 0.758 | 1 | 1.32 |
| Temperature −50 | 0.871 | 1 | 1.149 |
| Temperature +50 | 1.149 | 1 | 0.871 |
| Temperature +100 | 1.32 | 1 | 0.758 |
| Tint −100 | 1 | 1.32 | 1 |
| Tint +100 | 1 | 0.758 | 1 |
The gains act in linear light, before the picture is encoded again. A gain of 1.32 is 0.4 of a stop.
Which film type to choose
Choose Colour negative for film with an orange base, which is most colour print film. Choose Black and white for a negative with no colour, even if the scan has a tint: the tool reads the grey of each pixel and then inverts it. Choose Slide for a positive transparency, which needs no inversion and only the levels.
If a black and white negative looks flat after conversion, check the levels readout first. A narrow range means the points sit close together and Contrast is the better tool.
PNG or JPG for the result
PNG keeps every converted value as it is, so it suits a positive you will keep editing. JPG is written at quality 92 and is the smaller file for sharing. Both have the pixel size of the photo you dropped in, and both leave out camera data. The converter does not enlarge or crop.
Where the converter stops
It is a short method, not film software. The darktable manual describes sampling the unexposed film for a D min per channel, which I do here, and also sets a D max, an exposure bias and cast corrections for old film. I have only the base sample, automatic levels and the sliders. Treat the result as a very good first positive, not a measured one.
Tips for the converter
- Change the film type before the sliders, because switching it recalculates the levels.
- For black and white film, turn the automatic levels off if you want the plain inverse.
- Look at the levels readout: two close numbers mean a very flat scan.
- Keep PNG for the working copy and make the JPG at the end.
- A scan with a tint is still a good black and white negative; leave Temperature and Tint at zero.
Privacy
Your negative never leaves your device. It is opened, converted and saved in your browser, and nothing is uploaded.
Frequently asked questions
What does a negative to positive photo converter do?
It flips the tones of a negative so light areas become light again. For colour film it also removes the orange base first, which a plain flip of the tones would leave as a blue cast.
Does the converter work for black and white film?
Yes. Black and white mode reads the grey of each pixel and inverts it. A grey value of 200 becomes 55 with the levels off, and the base buttons are hidden because no base is needed.
Is there an online converter that needs no upload?
This one. The scan is opened, converted and saved inside your browser, and the page tests that no request carries image data. You need no account or software.
Can the converter handle slides?
Yes. Slide mode does not invert. It only sets the levels per channel, so a value of 100 with levels from 0.2 to 0.8 becomes 82, and a slide scan keeps its orientation of tones.
Is it as accurate as converter software?
Not for demanding work. Dedicated software such as darktable negadoctor has more controls and models film more closely. This converter is faster, free and in the browser, and it samples the base for every channel.
Related tools and guides
- Film Negative to Positive: Fix the Orange Cast: Convert a film negative scan or phone photo to a positive, with the orange base removed.
- Turn a negative photo into a positive in your browser: Photograph a negative with your phone or scan it, then turn it into a positive here. Tap the orange film edge, adjust the look and save the file.
- Image Resizer: Resize images by pixels, percentage or longest side.
- Image Cropper: Crop images to exact ratios or popular preset sizes.
- Put your photos together in one image: Join photos side by side, stacked or in a grid, with adjustable gaps and borders.
- Add text to your photo and keep it readable: Put captions on a photo with a gradient, tint or box behind them and a live contrast check.
- How I Edit Photos in GIMP: A Practical Workflow for GIMP 3.2: Another way to adjust levels and colour by hand.