Method for changing a natural image based on a light environment in the natural image

A method for changing a natural image comprising the steps of:

• dividing a natural image into a sky area and an object area;
• defining a sky model having at least one parameter selected from parameters representing (1) a position of a sun in a sky, (2) a color of sunlight from the sun, (3) a weather condition, and (4) a time of day;
• generating a fundamental sky image approximating the sky area of the natural image based on the sky model, the step of generating a fundamental sky image including the step of assigning a value to the at least one parameter of the sky model to enable the fundamental sky image to approximate the sky area of the natural image;
• generating a texture image representing differences between values of pixels in the sky area of the natural image and values of corresponding pixels in the fundamental sky image;
• changing the fundamental sky image by changing the value assigned to the at least one parameter of the sky model to a desired value;
• generating an image of a changed sky area by adding together the changed fundamental sky image and the texture image;
• generating a surface light source vector representing a color of a surface light source for illuminating the object area of the natural image from the changed fundamental sky image;
• generating a main light source vector representing a color of a main light source for illuminating the object area of the natural image from the sky model after the value assigned to the at least one parameter of the sky model has been changed to the desired value;
• and
• producing an image of a changed object area representing the object area of the natural image illuminated by the main light source and the surface light source by modifying values of pixels in the object area of the natural image in accordance with the main light source vector and the surface light source vector.