Colorization artists determine the accurate colors to use when colorizing black and white photos by considering various factors such as the lighting conditions during the time the photo was taken, the type of surface or material being photographed, and the overall tone and mood of the image. For example, if the photo was taken during the golden hour, the artist may recognize the long shadows and the orange glow in certain parts of the photo, and use this information to determine the appropriate colors to add. Similarly, if the photo was taken on a cloudy day, the colors may look washed out, and the artist would take this into consideration when selecting the colors to use.
When colorizing black and white movies, the process is different as the original colors are not known. The set, costumes, and makeup were designed to look good in black and white, not necessarily to have accurate colors. Therefore, colorization artists use their artistic judgment to decide on the colors to use, taking into consideration the style and tone of the movie, as well as the intended audience. They may also use software to color each pixel, which is then blended together to create a continuous image. Overall, the process of colorizing black and white photos and movies requires a combination of technical skill and artistic creativity to produce a final image that is both visually appealing and historically accurate.