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Imaging Principles Jul 21, 2017

Each film (including color film) consists of two basic components: a single layer or multilayer photosensitive emulsion layer, a photosensitive emulsion layer of the support body-the substrate. The emulsion is formed by suspending the fine particles of light sensitive to the gelatin medium. The gelatin on the film is similar to the gelatin used in certain foods.

The photosensitive substance suspended in gelatin is silver halide particles. This particle is so microscopic that it can only be observed at high magnification. In the 1-square-inch photographic film emulsion, the content of silver halide crystals is approximately 40 billion.

Silver halide crystals have properties that change as soon as their structure is exposed. The mechanism of the change of chemical properties is not important to us, the final effect of the change is the most important. How did this change come about? When you shoot, the light shoots through the camera's lens onto the emulsion layer of the film, and the clumps formed by the silver halide crystals when the light arrives at the silver halide crystals are still extremely tiny. The change and coalescence of the amount of light received by the emulsion layer. That is to say, different intensities of light on the film, film emulsion layer in the microscopic field of different quantities of crystal structure changes and mutual coalescence.

Once the film is exposed, it immediately produces a latent shadow-an invisible image. The film must be developed in order to convert the shadow into a visible solid image. When the film developed, the structure has changed the silver halide crystals are converted to ferrous metal particles of structure, resulting in image-negative images. Those that are not photosensitive on the film, i.e. crystals that do not have structural changes, are washed away by a chemical called a fixer, making these parts light or transparent. The result is a negative image of the dark (thick) part of the exposure of more parts, the bright (thin) part is less exposure, the whole transparent part is not exposed to light. This is the basic process of black recording images.

The color film has a three-layer photosensitive emulsion layer, in which the emulsion layer also contains different organic compounds capable of producing dyes, called color coupling agents (couplers). They are colorless in nature, but can be coupled with the oxide of the color developer in color development to become colored dyes. For the negative film, the upper layer blind emulsion contains the mixture in the color development of yellow, middle formation magenta, the lower layer to form cyan, this is the color film we have been developed. By printing or enlarging the image onto the photographic paper or by film reverse flushing, the yellow layer of the film is converted to its complementary color blue, the middle one is green, the lower level turns to red, we get the same colour photograph or transparent film as the natural state. This is the basic process of color film recording images. In a previous black-and-white film shoot, the director used the film to record the plot of the movie.

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