The first colorization was performed absolutely manually using aniline dyes for film. Then it was a very time-consuming process, because each frame had to be drawn with hands. At the beginning of the XX century the process of transforming black and white frames became somewhat more technological and special stencils were used for painting. In the mid-20th century, the first colorized frame of the cartoon appeared.
The manual decoration was replaced by digital colorization. For the first time, computers were used in 1970 and the process has not changed fundamentally.
First, a high quality digital copy is made using the scanner. A mask is created for each frame with the help of the corresponding software, and the necessary colors will be distributed. The mask of one frame serves as a mask for later ones.
Next, the black-and-white basis merges with the color information of each area of the film. Image processing takes place and a color film is obtained. Using this technology initially turned out rather muted tones, but with the development of computer technology movies began to look more plausible.
The main problem of colorization is the great cost of labor. Each frame needs to be divided into many zones, which often have to be marked manually, because automatic selection of the boundaries of significant areas is not always possible due to the blurring of the frame or the presence of complex, small details in the image.
Various companies are still developing technologies to improve the colorization process. So, some corporations use neural networks to highlight lines and objects. Different mechanisms are also created to recognize the shapes of objects on a frame that can change the shape of masks on each frame.