Multispectral photography

To record and reproduce the colors of natural objects, we can use multispectral photography technology according to the principle of color vision, that is, through the decomposition and synthesis of color light.

Multispectral photography has three basic contents:

(1) Decompose the color of the scene through the color filter;

(2) film processing;

③ Color synthesis in additive photography system.

Suppose we take a group of chromatographic photos with additive photography, and the composition of this group of chromatograms is shown in Figure 2- 17(a). In order to obtain the color separation film shown in Figure 2- 17(b), the following methods should be adopted:

(1) Add a red filter to the lens of the camera, put on a black-and-white negative, and take photos of the scene;

(2) Don't move the camera, use a green mirror instead of a red filter, and then take photos of the scene with a black-and-white negative;

(3) Replace the green filter with the blue filter, then shoot the scene and develop three negatives, with the density as shown in Figure 2- 17(b).

Before color projection, print the negative into a positive film, as shown in Figure 2- 17(c). Obviously, the image density (or gray scale) of positive film is just the opposite of that of negative film.

Figure 2- 16 tricolor schematic diagram

Fig. 2- 17 color reproduction using additive multispectral technology

Then recombine the images of the three positive films on the observation screen as follows. Put three positive films into three projectors respectively (Figure 2- 17(d)), and put red, green and blue filters in front of the light source of the projector. Adjust the three projectors to make the three projected images on the screen strictly coincide. According to the principle of additive color reproduction, three positive images are synthesized by projection to reproduce the color of the original scene (Figure 2- 17(d)). As can be seen from the above, multi-spectral photography can accurately reproduce scenes of various colors. Color synthesis of optical processing of remote sensing images (see Chapter 6, section 1) is to enhance some information on the images by using multispectral photography (Table 26-).