The concepts, expressions, decisive factors and influencing factors of optical density and contrast are briefly described.

The concepts, expressions, determining factors and influencing factors of optical density and contrast are as follows:

1. Optical density refers to the darkness or opacity of transparent photos, also known as blackness or photo density, which is expressed by the logarithmic value of light blocking rate, that is, D=lgI0/I, dimensionless.

2. Contrast refers to the difference of image density between two adjacent parts of a photo, which is expressed by k, that is, K=D2-D 1 1.

3. The decisive factors of optical density are tube voltage (kV), tube current (mAs), photographic distance (FFD), sensitivity of intensifying screen (F), film sensitivity (S), thickness and density of subject, post-processing factors (developer characteristics, developer temperature and development time) and so on.

1, tube current (mAs): increasing the tube current can improve the density of the photo, but at the same time it will also reduce the contrast of the photo.

2. Tube voltage (kV): Increasing the tube voltage can improve the contrast of the photo, but at the same time it will also reduce the density of the photo.

3. Shooting distance (FFD): Increasing the shooting distance can improve the contrast of photos, but it will also reduce the density of photos.

4. Sensitization ratio (f) of the intensifying screen: increasing the sensitization ratio of the intensifying screen can improve the density of the photo, but at the same time it will also reduce the contrast of the photo.

5. Sensitivity of film: Increasing the sensitivity of film can increase the density of photos, but it will also reduce the contrast of photos.

6. The thickness and density of the main body and the post-processing factors of the photo (developer characteristics, developer temperature and development time), etc. These factors have a certain influence on the optical density and contrast, and need to be properly controlled and adjusted.

Four, the decisive factors of contrast are X-ray contrast, film gamma, line quality, line number, scattered lines, post-processing technology of photos and the subject itself.

1, x-ray comparison? . X-ray contrast is the biggest factor that affects the contrast of photos.

2. What is the film gamma value? . The greater the film γ value, the greater the photo contrast.

3. Linear mass and linear quantity? . The harder the line quality, the greater the number of lines and the greater the contrast of photos.

4. Scattered lines? . Scattered lines will reduce the contrast of photos.

5. The post-processing technology of photos and the factors of the subject itself? . The influence of post-processing technology and the factors of the subject itself on the contrast of photos is complex and needs to be analyzed in detail.

Application of contrast

1, image enhancement: In digital image processing, contrast is an important means of image enhancement. By adjusting the contrast of the image, the details in the image can be clearer, thus improving the quality and clarity of the image.

2. Image segmentation: In image segmentation, contrast can help distinguish the contours and edges of different objects. By adjusting the contrast, the difference between different objects can be more obvious, so it is easier to segment the image.

3. Color correction: In digital image processing, contrast can also be used for color correction. By adjusting the contrast, the color in the image can be more vivid and true, thus improving the color reproduction degree of the image.