Five effects, one pass
Inverting subtracts each colour channel from its maximum, so black becomes white and every colour becomes its opposite. Greyscale drops the colour and keeps the brightness. Sepia maps the image onto a warm brown range. Inverted greyscale combines the first two. Threshold pushes every pixel to pure black or pure white against a cut-off.
A strength setting blends any of them back toward the original, which is what makes inversion and sepia usable as a treatment rather than a novelty. At full strength most read as obviously applied; at a third they read as a deliberate grade.
The [msm_tool slug="image-inverter"] does all five in a single pass over the pixels.
Inversion is a negative, and negatives are for inspecting
The most useful applications are diagnostic rather than decorative.
- Scanned film negatives. Inverting a scan of a negative gives the positive image. This is the original purpose and it still works.
- Checking a design reversed out. Inverting a layout shows immediately whether it survives being used light-on-dark, which is a question every design now has to answer.
- Finding faint detail. The eye is better at distinguishing dark tones than light ones, so inverting a very light image can reveal detail that was invisible — useful on faded documents and overexposed scans.
- X-rays and technical scans, where inverting is a standard viewing mode rather than an effect.
Threshold destroys information deliberately
Every pixel becomes one of two values. That is the point for line art — logos, signatures, scanned drawings, anything heading for a stencil or a single-colour print — and it is useless for photographs.
Adjust the cut-off until the strokes hold together without the background breaking up. On a scan with uneven lighting there may be no single value that works across the whole page; at that point the answer is a better scan rather than a better threshold.
Greyscale is not desaturation
Brightness is computed with the channels weighted for how the eye responds — green counts for far more than blue. That preserves the tonal separation between colours that a naive average flattens.
A pure red and a pure blue have identical average values and look nothing alike. Under an average they become the same grey; under proper weighting the red stays light and the blue stays dark, and the image keeps its structure.
Sepia is a look, not a repair
It makes a modern photograph resemble an old one. It does nothing for a genuinely old photograph, which usually needs contrast and dust removal rather than more brown.
Used at full strength it is a period pastiche. Used at a quarter, it is a warm grade that reads as intentional rather than as a filter someone found.
Transparency and format
PNG and WebP keep the alpha channel. Choosing JPEG flattens the image onto white first, since JPEG has no transparency — so an inverted logo with a transparent background will arrive with a white one.
Worth thinking about with inversion specifically: inverting an image with transparency inverts only the visible pixels. The transparent regions stay transparent, which is usually right and occasionally surprising when the result is placed on a dark background.
Dark mode is not an inversion
It is tempting to invert an interface screenshot and call it a dark theme. Inverting turns brand colours into their opposites, photographs into negatives, and carefully chosen accents into something unrecognisable.
Dark mode is a separate set of colour decisions against the same palette. Inversion is a quick way to see whether a layout's structure survives — not a way to produce the theme itself.