What is digital photography? Pixel, white balance, what do you mean? (noun explanation)

1. Definition of digital photogrammetry

At present, there are two main views on the definition of digital photogrammetry in the world.

A. Digital photogrammetry is a branch of photogrammetry. Based on the basic principles of digital image and photogrammetry, it applies the theories and methods of computer technology, digital image processing, image matching and pattern recognition to extract the geometric and physical information of the subject in digital form. The United States and other countries call it soft copy photogrammetry, and Professor Wang calls it full digital photogrammetry. This definition holds that in the process of digital photogrammetry, not only the product is digital, but also the original data of intermediate data recording and processing are digital.

B Another definition only emphasizes that the intermediate data record and the final product are in digital form, that is, digital photogrammetry is a branch of photogrammetry that uses computer technology to extract the geometric and physical information of the subject from images (including hard copies, digital images or digitized images) in digital form. The definition of digital photogrammetry includes computer-aided mapping (usually called digital mapping) and digital image mapping.

Digital image mapping is to process digital images or digitized images with computers, and replace the stereoscopic measurement and recognition of human eyes with computer vision (the core of which is image matching and image recognition), so as to complete the automatic extraction of geometric and physical information of images.

Another type is called hybrid digital photogrammetry. Usually, a pair of CCD digital cameras are installed on the analytical mapper to digitize the local image to be measured and obtain the coordinates of the points through digital correlation (matching).

2. The English name of White Balance is White Balance. The color of the object will change due to the color of the projected light, and the photos taken under different light conditions will have different color temperatures. For example, a photo taken under the illumination of tungsten lamp (light bulb) may be yellow. Generally speaking, CCD can't automatically correct the change of light like human eyes. Balance means that the digital camera defaults to "white" regardless of the ambient light, that is to say, it can recognize white under colored light and balance the tones of other colors. Color is essentially an explanation of light. What looks white in normal light may not look white in dark light, and "white" under fluorescent light is also "non-white". If the white balance can be adjusted for all this, other colors based on "white" can be correctly restored in the obtained photos. At present, most commercial digital cameras provide white balance adjustment function. As mentioned above, the white balance is closely related to the surrounding light, so the use of the flash will be restricted when the white balance function is started, otherwise the change of ambient light will invalidate the white balance or interfere with the normal white balance. Generally, there are many modes of white balance, which are suitable for different scenes, such as automatic white balance, tungsten wire white balance, fluorescent white balance, indoor white balance and manual adjustment.

3.Pixel and pixel are composed of the letters of the words "Picture" and "Element", which are the units used to calculate digital images. Like photographs, digital images have continuous shadows. If you enlarge the image several times, you will find that these continuous tones are actually composed of many small squares with similar colors, which are the smallest units of the image. This smallest graphic unit can usually display a coloring point on the screen. The higher the pixel, the richer the sample and the more realistic the color is. Pixel is usually considered as the smallest complete sample of an image. This definition is very relevant to the context. For example, we can say that pixels in a visible image (such as a printed page) are pixels represented by electronic signals, pixels represented by numbers, pixels on a display or pixels in a digital camera (photosensitive element). Many other examples can be added to this list. Depending on the context, there will be some more accurate synonyms, such as pixels, sampling points, bytes, bits, dots, spots, supersets, triples, edge sets, windows and so on. We can also discuss pixels abstractly, especially when using pixels as a measure of resolution, such as 2400 pixels per inch (ppi) or 640 pixels per line. Dots are sometimes used to represent pixels, especially computer marketers, so ppi is sometimes written as DPI (dots per inch). The more pixels used to represent an image, the closer the result is to the original image. Although there is a more specific definition of resolution, the number of pixels in an image is sometimes called image resolution. Pixels can be represented by a number, such as a "3 megapixel" digital camera with a rated pixel of 3 million, or by a pair of numbers, such as a "640 × 480 display" with 640 pixels in the horizontal direction and 480 pixels in the vertical direction (just like a VGA display), so its total number is 640× 480 = 307,200 pixels. The color sampling points of digital images (such as JPG files commonly used in web pages) are also called pixels. Depending on the computer monitor, these pixels may not have a one-to-one correspondence with the screen pixels. In this obviously different area, the points in the image file are closer to the texture elements. In computer programming, an image composed of pixels is called a bitmap or raster image. The word grating comes from analog TV technology. Bitmap images can be used to encode digital images and some types of computer-generated art.