http://dev.gameres.com/program/visual/3d/EXPOSURE.HTM World looks like? Yeah, there are some things in this world look so dark, such as cave, coal, evening bed Wait. Some things are not so dark even at night, such as sand, and face. Some parts are bright, white shirts, snow, light bulbs, and some things are of course very dazzling, such as spotlights, sky, sun And lasers, etc. Is computer graphic look? There is a brightness range that is displayed on the display, which is generally 255, from 0 (black) to 255 (white), now our head There have been these concepts, so how can I create a real world image on the computer screen? The natural world has a wide range of brightness, but the computer can only display them very narrow part, you may need Reduce the brightness of the real world to adapt to him, such as using 0 to express a very dark cave, and use 255 to express the sun. But if you do this, you will encounter very serious problems when you express images, such as people face It will become very dark. For example, the following:
The brightness of the sun is assumed to be 255. It can be seen that the sun's performance is very beautiful, but the sky is very dark, and even like the evening. One choice is to cut the brightness value, for example, if an object is more than snow If you want to be white, give him a brightness of 255. You can see this picture below:
Now the ground looks great, but the sky looks unusually bright, even all white. You will not see the sun, and the clouds are like a window on light blue Beijing. I want to ask again. One problem, how is the photo look? Just like a computer screen, the camera can only show a narrow range for brightness. In photos, the darkest thing does not look very black, and the brightest part It will not be a bright environment than him (the translator's note: the original is Environment, you should understand a small piece of space around this object). But why didn't the photo do not encounter the problem mentioned? In fact? The photo also has a similar problem, but in handling such a large range of brightness, the camera is doing very well. Different cameras also have exposed control. If you understand these, you will help us better understand the generation. Take photos The process: When the photo is photographed, the shutter only opens a very short time to enable a small amount of light into it. The light is focused by the camera lens into a slightly photolithography film. Once the film is protected under light, the chemicals contained in the film Will decompose, the image recorded on the film will also be destroyed, and the possible photos will be brighter. The light entering the camera lens can be controlled by the shutter time and the aperture size. The film is then stopped and the color is developed. This is a negative piece. This is a photo with a light bulb. So, then what is the relationship with the computer graphic? The simplest photo model tells us why the camera should be good at a wider range of brightness. Let us consider the exposure of the scene light. Imagine with a 100W mol of photosensitive chemicals on a fast small film. Light falls in that area, there is 50W mol substance to decompose, so he can only The image of half brightness is displayed. If the same number of light falls on this area, there are half of the chemical substance decomposition, the remaining 1/4, the image will be 75% brightness. As more and more Multi-light falls in this area, more and more chemicals will be decomposed. However, as increasing chemicals exist on this area, decompose the same substance, you need more light.
