Negative Image Converter

What inversion is, in one line of arithmetic

Each pixel stores three numbers from 0 to 255 — how much red, green and blue it contains. Inverting replaces each with 255 minus itself. That is the whole operation. Because subtraction is exact, nothing is lost: invert a file twice and you get back the identical original, byte for byte, provided you save losslessly in between.

The visual effect is that every colour swaps for its complement. Red becomes cyan, green becomes magenta, blue becomes yellow, and anything grey stays grey but flips between light and dark.

Scanning film negatives

This is where most people arrive. You have a shoebox of negatives, a flatbed scanner, and a set of scans that look like orange ghosts. Two things are going on.

• The image is inverted — bright becomes dark, which is the point of a negative.
• Colour film has an orange base, a deliberate mask built into the emulsion to correct for impurities in the dyes. Invert it naively and that orange becomes a strong blue cast over the whole frame.

The film mode above handles both: it finds the brightest value in each channel — which on a negative scan is the unexposed film base — and divides it out so each channel is normalised before the inversion. That is essentially what dedicated scanning software does, and it gets you to a usable positive in one step. Black and white negatives have no mask, so plain full inversion is correct for them.

After inverting, expect to need contrast. Negatives are low contrast by design, because the film holds far more range than a print does. Lifting contrast to 120-150% is normal, not a sign you did something wrong.

Scan settings that make the rest easier

• Scan at 2400 dpi or higher for 35mm. A frame is only 36 by 24 millimetres, so resolution is the whole game.
• Turn off the scanner's own automatic colour correction and dust removal for the first pass — you can always add them, but you cannot undo them.
• Save the raw scan as TIFF or PNG, not JPG. Everything you do afterwards is easier on a lossless file.
• Keep the negative flat and clean. Dust shows as white specks after inversion, which is far more obvious than dark ones.

Other reasons to invert

• Reading faint documents. Light pencil on white paper is often far easier to read as white on black.
• Dark-mode graphics. Inverting a simple black-on-white diagram is the quickest way to get a usable dark version, though it will flip your brand colours too.
• Screen printing and stencils. Many processes need the artwork the other way round.
• Checking a design. Inverting a layout is a decades-old trick for spotting balance problems your eye has stopped noticing.
• Astronomy. Faint detail in a star field is frequently easier to see inverted.

Save as PNG if you are not finished

The inversion is exact, but saving as JPG afterwards is not — it adds a fresh round of lossy compression on top of whatever the original already carried. If the inverted file is going into an editor for more work, save it as PNG. JPG is fine once you are done and just want to share it.