图片反色

Photograph or scan a strip of film and invert it to see the picture as a positive. Black-and-white negatives come out well straight away, often needing only a contrast tweak. Colour negatives are trickier: the film base has an orange mask, so a plain inversion gives a strong blue-cyan cast. Inverting still tells you what is on the frame, which is enough to decide which negatives are worth a proper lab scan; correcting the colour itself needs an editor with white balance or curves.

For the best result, light the film evenly from behind, for example with a tablet showing a white screen, and crop away the film edges before inverting.

A screenshot of a dark-mode app or code editor is mostly black, which wastes toner and prints muddy. Inverted, the background turns white and the light text dark, so it reads like a normal page. Coloured syntax highlighting changes hue too, blue becoming orange and green becoming magenta, so check that the colours still make sense.

PNG keeps screenshots pixel-exact. For an opaque PNG, running the result through a second time gives the original pixels back exactly, because 255 − (255 − v) = v. JPG and WebP add a little compression loss on each save.

Only the colour channels change. The image keeps its width and height, transparent areas of a PNG stay transparent, and semi-transparent edges keep their opacity, so an inverted logo still sits cleanly on a page. This is the same arithmetic as the CSS filter invert(100%) and the Invert command in most editors. It is not the smart invert of a phone’s accessibility settings, which leaves photos untouched; here every pixel is flipped.

A JPG stays close to its original size, because the amount of detail does not change: a 224,092-byte test photo came out at 222,771 bytes. A PNG can grow, because the browser’s PNG encoder packs less tightly than many editors; a 1,601,750-byte PNG photo was saved at 2,088,432 bytes. EXIF data, including GPS location, is not copied to the new files.

Because transparency is kept, inverting is a quick way to make a light variant of a dark icon or logo saved as PNG with a transparent background. A black mark turns white and its soft anti-aliased edges keep their opacity, ready for a dark website footer, a slide with a dark theme or a watermark on a dark photo. Grey parts of the logo flip around the middle: 30% grey becomes 70% grey, and a mid-grey of 128 lands on 127, so check those in the preview.