Development Status and Prospects of Digital Imagery

With the end of the first year of the new millennium, mankind ushered in the new century. Looking back at the entire twentieth century, the greatest advancement of mankind in the field of science and technology is not the bombing of atomic bombs and the astronauts of space shuttles. It is the development of information technology; the most important breakthrough in human art is not film and television. The invention and development of technology, but the birth of digital video technology. Digital imagery is the result of a perfect combination of true science and technology and culture and art: it is the product of a true information revolution.

Broadly speaking, digital video technologies include digital television technologies (such as VCD, DVD, high-definition television and digital television transmission, etc.), digital cinema technologies (such as computer production, computer special effects and computer animation, etc.), digital printing technologies, and computers. Drawing technology and digital photography technology. The digital image technology we are talking about here mainly refers to digital photography technology. It includes digital photography technology, digital scanning technology, digital printing technology, computer production technology and digital darkroom technology.

First, the development and application of digital cameras

Since the French inventor Daguell invented "silver photography" in 1839, humans have always used photographic techniques that use silver halide as a photosensitive material. This phenomenon was not broken until the 1970s. At that time, due to the development of space technology, humans had to develop a photosensitive material instead of film in order to send images to the ground at any time. This is the original digital photography technology. Digital photography technology was used in the civilian field. It was started in the 1970s. It began to be developed in the 1980s and was officially put into production in the 1990s. Until 1993, digital cameras produced and sold in the world were less than 30,000. Year-on-year sales of digital cameras reached 100,000 units. In 1995, they exceeded 340,000 units. In 1996, they suddenly increased to 1.1 million units. In 1997, they reached 1.9 million units. 3 million units have reached 4.3 million units in 1999 and are expected to exceed 6 million units in 2000. However, as of October 2000, digital cameras have sold more than 7 million units. (In 2000, the data was developed on a weekly basis. It must be finalized before printing.) According to optimistic estimates of the industry, before 2002, the digital counterparts will enter the Chinese ordinary people's households. Before 2005, the digital figures will meet each other. Will be popular in the country. At that time, digital cameras will develop to a fairly mature level, and prices will also be greatly reduced. In 2010, digital cameras will occupy the vast majority of the camera market.

(A) The basic principle of digital cameras

1. Digital Camera CCD

The core part of a digital camera is a photosensitive device called CCD, which replaces traditional photographic film. CCD is the abbreviation of English Charged Coupled Devices, which means rechargeable charge couplers. This is a kind of "Metal-Oxide-Semiconductor" (MOS) integrated circuit device, which is composed of a large number of tiny optoelectronic coupling units, and the size of each unit is only a few micrometers to more than ten micrometers. A CCD chip is composed of hundreds of thousands, millions or even tens of millions of such photoelectric cells, and its small area is less than one square centimeter, and large ones can reach more than ten square centimeters. The digital camera's CCD area is usually only 4x6mm (1/2") to 6x9mm (2/3") far smaller than the area of ​​135 camera film, but the digital back CCD installed on the 120 SLR camera can Achieve 30×30mm to 40×40mm, it is close to 120 film area. The CCD chip is placed in the position of a conventional camera for film release.

The image formed by the lens is projected onto the CCD element. The CCD converts its optical signal into an electrical signal. The analog signal is converted into a digital signal by an analog-digital conversion circuit in the digital camera, and then stored on the magnetic card or Enter it into your computer. This digitalized image can be processed by computers in various special ways. It can be displayed on a computer monitor or printed out on a printer. It can also be printed on a printer or projected using a projector.

2. The number of pixels in the digital image

Each photoelectric element of the digital phase-coupled CCD chip records a tiny element of the image. The color and brightness of the image in this element are exactly the same. A digital image is composed of thousands of such tiny elements. Each tiny element of a digital image is called a pixel of the image, symbol P. Each micro-optical unit of the CCD records one pixel of the image. The more photoelectric element units of the CCD, the more pixels of the digital image, and the more delicate the image, the clearer it looks.

The number of pixels in the digital image is represented by the number of horizontal photovoltaic cells (H) on the CCD chip multiplied by the number of vertical photovoltaic cells (V). This is very similar to an image of a television set, with vertical (V) 625 scanning lines, and horizontal (H) lines can have a maximum of 800 points, and thus can be written as 800 (H) x 625 (V). The reference for the number of digital image pixels is 768 horizontal scanning points and 512 vertical scanning lines, and the multiplication is a total of 393,216 pixels. That is, 768 (H) × 512 (V) = 393,216 (P).

In the computer field, due to the large amount of data, the number of units is also set large, generally 1,000 (actual 1,024) as 1K; and ,000,000 (ie 106) as 1M, Called 1 trillion; write 1,000,000 for 1,000,000,000 (ie, 109). At the same time ignore the last few decimal places. The current digital image has a 1/16 reference, a 1/4 reference, and a 4x reference, a 16x reference, a 64x reference, and even a 256x reference.

Their number of pixels is:

1/16 benchmark: 192 (H) × 128 (V) = 24.58K (24K);

1/4 reference E384 (H) × 256 (V) = 98.30K (100K);

Benchmark: 768 (H) × 512 (V) = 393K (400K);

4 times the benchmark: 1,536 (H) × 1,024 (V0 = 1.57K (1.6M);

16 times the benchmark: 3,072 (H) × 2,048 (V) = 6.29 (M) (6M);

64 times the benchmark: 6,144 (H) x 4,096 (V) = 25.17 (M) (25M);

256 times the benchmark: 12,200 (H) x 8,192 (V) = 100.660 (M) (100).

The current 256-times reference CCD has only linear arrays, that is, the CCD is composed of 8192 tiny photoelectric cells that form a linear element. By scanning, the number of pixels reaches 12,200×8,192=100M.

3. Digital phase number of color

In the computer field, the smallest unit of data volume is "Byte" and the symbol is B. One byte is composed of binary 8 digits. Each bit of the binary system is called a "bit" and is represented by a symbol bit. One byte is 8 bits, that is, B=8 bit. For example, a Chinese character is composed of 2 bytes, that is, 1 Han Ding occupies 16 bits. Every pixel in a digital camera contains many colors. For example, each color of red, green, and blue can range from light to dark. The type of color contained in each pixel can also be represented by the number of bytes or bits. Generally, a monochrome CCD contains at least 8 bits of color per pixel. 8bit is 28 which is equivalent to decimal 256, which means 8bit black and white color is equivalent to 256 colors from white, light gray, medium gray, dark grey to black. The color CCD chip is composed of three basic colors (three primary colors): red, green, and blue. Each color has at least 8 bits of color. That is, each color of red, green, and blue is 256 colors from light to dark. Color composition. Then they can make up a total of 256×256×256=2563=28×3=224=16,777,216 colors, ie about 16 million (16M) colors. We say that its CCD has 24bit color, or its CCD has a 24-bit color depth. For the computer, 24bit color is 3 bytes, so a 6M pixel digital face, because each pixel accounted for 3 bytes of "document volume", so the camera photographs, if not shrink, then Occupy 18M files. Some digital cameras, each of red, green, and blue, have 10 bits or even 12 bits of color. Therefore, the color depth or "color bit number" of this camera is 30 bits to 36 bits. A 6M pixel 36bit digital camera requires 27M files per shot.

(B) Digital Camera Specifications

Digital technical indicators are mainly optical resolution and color number. The optical resolution of a digital camera mainly refers to the total number of pixels of its CCD chip. The number of pixels in digital cameras has grown from the initial number of hundreds of thousands, more than one million, to the current two million, three million, four million, and professional cameras have reached more than six million. The number of pixels in static scanning digital cameras has reached 24 million, or even more than 100 million. Digital cameras generally have 24 bits of color, high-end digital cameras have 30 bits, and professional digital cameras have 36 bits of color.

Other technical indicators of digital cameras include:

1. Liquid display area. Digital cameras currently have almost all LCD screens so that they can be seen instantly. At present, the main dimensions of the LCD display are 1.8 inches and 2 inches.

2. CCD chip area, digital camera's core technology is CCD chip. The larger the area of ​​the CCD chip, the higher the cost will be to accommodate more pixels. The current CCD area mainly has the following specifications: 1/2 inch (4.5 x 6.75 mm), 2/3 inch (6 x 9 mm), 14 x 21 mm, and 18 x 27 mm.

3. The optical zoom range of the lens, the general digital camera has two kinds of optical zoom and digital zoom zoom. The so-called "digital zoom" is the artificial insertion of some pixels through the computer chip to enlarge the image. So the key technical indicator of the digital camera is its optical zoom range. Normal digital cameras have twice the zoom function, and some digital cameras have three times the zoom function.

4. The focal length of the lens. In general, a digital camera has a small area of ​​a CCD chip and needs to cover the same range of scenes, and the focal length of the lens is generally short. Some digital CCDs have a larger area and the focal length of the lens is longer. Therefore, the absolute value of the lens focal length of a digital camera does not make sense. It is meaningful to use it to capture the range of scenes covered by the lens. In general, a digital camera does not specify the actual focal length of the lens, but only the value corresponding to the focal length of the 135 camera lens. This value is called the “equal focal length” of the digital camera. For example, the actual focal length of a digital camera lens is 9-27mm, and its CCD chip area is only 6 × 9mm (1/4 of the 135 film frame), its equivalent focal length is: 36-108mm, 35- 70mm, 35-105mm and so on. Inside the professional digital camera there is a device called a "focaller", which can reduce the image of an ordinary 135 camera lens to the CCD chip in the same range. Because it can directly install a 135 SLR camera lens, it The focal length of the lens is equivalent to the focal length of the mounted lens.

5. The shutter speed, digital camera shutter speed concept is exactly the same as the traditional camera. Due to the different photosensitivity of the CCD chip, the range of shutter speeds of digital cameras of different grades is also different. For example, some digital cameras have a shutter speed of 1/4 second - 1/400 second, some 1/2 second - 1/362 second, and some are 16 seconds - 1/400 second. In general, the maximum shutter speed is not fast. The shutter speed value of digital cameras is generally continuously adjustable, so its sub-range is also slightly different from the traditional camera, such as the traditional camera shutter time is not accurate to 1/332 second. Digital camera shutters are generally electronic shutters, so the time accuracy is very high.

6. Lens aperture. Like the shutter, the aperture of a digital camera is generally an electromagnetic diaphragm, so its value can also be continuous, and the grading is also different from the traditional lens aperture. In their zoom lens, the aperture is mostly drift (except for professional SLR type digital cameras). For example, the maximum aperture at the wide-angle end is F3.0, and some are F4.0. The minimum aperture is F13.5, some is 14.0; the maximum aperture of the telephoto end is F3.9, some F4.7, the smallest aperture is F16.0, some F22.0 .

7. The equivalent sensitivity, because the digital camera's photosensitive element is CCD, so it is equivalent to the traditional photographic film "equal brightness." The equivalent sensitivity of the CCD chip is equivalent to the ISO50 of the traditional film sensitivity, and some of the phase