How does AI colorize manga? A plain explainer
How an AI colorizer turns black-and-white manga into color: what the model sees, how it picks colors, why hints help and where it goes wrong.
An AI colorizer works by predicting a color for every region of a black-and-white page, based on what it learned from many pairs of black-and-white and colored images. It finds shapes such as hair, skin and sky, guesses a likely color for each and paints them under the line art. RuneManga's own colorizer is in development; this is how the technique works in general.
This is a general explainer. RuneManga's colorize mode is planned, not available yet, so it should not be read as a description of something you can use today.
What the model sees
The input is a grayscale page: black line art, white paper and screentone. The model has no color to start with, so it has to work out what each shape is from its outline and surroundings. A round shape at the top of a figure, framed by long lines, is probably hair. A flat area behind the figure is probably a wall or a sky.
How it picks colors
During training, the model is shown a very large number of examples: a colored image and the same image turned into black and white. It learns which colors usually go with which shapes. At use time it applies those habits to your page. It is a prediction, not a lookup, so the same character can end up with a slightly different shade each time.
Why line art and screentone matter
- Line art tells the model where one region ends and the next one begins. Clean, closed lines produce clean color areas, and broken lines let color leak.
- Screentone is a printed dot or line pattern used for shading. To a model it can look like texture or like noise, and it can produce dirty or blotchy color. Some colorizers remove or smooth tones first.
- Text is a nuisance. Letters in a bubble can get colored like part of the picture, which is why RuneManga's planned order is to erase lettering before colorizing.
Automatic, hints and references
- Automatic: the model chooses everything. Fast, and the easiest to get wrong.
- Hinted: you place a few color strokes or points, and the model spreads them over the shapes. This gives you control over hair and clothes.
- Reference-based: you supply a colored picture of the character and the model tries to match it. This helps with consistency.
Where it goes wrong
- Wrong colors for important details, such as a character's eyes.
- Colors that change from one page to the next, because each page is predicted on its own.
- Spills across gaps in the line art.
- Muddy or noisy areas where screentone was.
- Colors that do not fit the scene's light, for example a night scene painted in daylight colors.
What it can't know
A model cannot know what the artist intended. If a character's hair is silver in the story but the page is black and white, the model cannot see that. It can only guess from habits learned in training, which is why a few hints or a reference picture often make a large difference.
How this fits into a translator
Translating and colorizing are separate jobs, and the order matters. Reading the text works best on the original black-and-white page, and colorizing works best on a page with the old lettering removed. So the sequence is: read, translate, erase and rebuild, colorize, then typeset the translation on top. RuneManga plans to do all of this in one run once colorize is ready.
Questions
Is AI colorized manga the artist's real coloring?
No. It is a prediction made by a model. Official color editions are made by or with the artist and a colorist.
Why do some AI colorings look flat?
The model predicts regions of color and may not add the shading and lighting a colorist paints by hand.
Does it work on any manga?
It works best on clean line art with clear outlines. Busy screentone, rough scans and unusual styles are harder.
Does RuneManga colorize manga?
Not yet. Colorize is planned, not available yet, and the colorizer is in development. Translate is the mode to use today.