Digital camera basics

 (Charge Coupled Device), or for capturing graphics, widely used in scanners, copiers and no film cameras and other equipment. and the film's principle is similar to the light through a lens, will be projected onto the CCD on the graphic information. But the difference is with the film, CCD neither ability to record image data, no ability to permanently preserved, or even do not have the (such as memory chips or memory card). CCD with a variety of sizes and shapes, the largest square inch with 2t2.
CMOS
CMOS (Complementary Metal Oxide Semiconductor), or .
White Balance (White Balance)
in different lighting conditions, due to different color temperature, color cast photo is taken out. If the color temperature is low in red light, yellow light content is more, the color photographs will be reddish and yellow, the color of light in the high culture of blue, green more photos will be bluish and green. At this point we need to use the white balance function to amend, its principle is to control the light in the red, green and blue Three color brightness, the image light level reaches the largest white, can make other colors accurately.
Interpolation (Interpolation)
not generate pixels in the case of image pixels to increase the size of a method In the surrounding pixels based on the color of a mathematical formula to calculate the color pixels is missing. Some cameras use interpolation to artificially increase the image resolution system.
Bit (bit)
This is the computer image of the term used to describe the resulting image can contain the number of colors. all is made of red, green and blue three colors mixed together,Bailey UGG boots, so the color of the image contains up to 256t256t256 total of 167 million kinds, that is, the so-called 24-bit color.
TWAIN
This is a digital camera very common technique in a word. TWAIN is a special kind of software, with it, other TWAIN-compliant software can share the image resources. For example, PaintShopPro, this is a good sharing of image processing software, it can work with TWAIN devices. PaintShopPro so you can directly use digital camera images. TWAIN devices including scanners, fax machines, of course, a digital camera.
distinguish between CCD and CMOS
Image Processing industry in 1970 is a landmark year, Bell Labs invented the CCD. Twenty years later, people use this technology to produce a digital camera, the image processing industry to promote a new field. Digital Camera No film and rinse, repeat shooting and instant adjustment; images can be copied infinitely without loss of quality, easy to permanent preservation, can be used for electronic transmission and processing. its birth to the image processing industry has brought a revolution. < br> And then, it was found that the computer system for processing a chip can be used as sensitive sensors in digital cameras, the CMOS, the ease of mass production and low cost characteristics are businessmen dream of. industry analysis, It is possible in the near future to replace CCD, the two still exist today. Many people think:
> And is not the case: light sensor, in particular CCD, the camera's function is to capture through the lens of the light and converted to electronic signals, not so much the heart of digital cameras, digital camera, as it is the eyes. In research grade webcam, CCD or CMOS light sensor, although very important components to a large extent determines the camera's pixels, but the CCD / CMOS chip in the cost of the camera is not the dominant position, particularly The more areas in the high-end performance of the more prominent this feature.
comparison from a technical point of view, CCD and CMOS has four different aspects:
information read mode
CCD charge-coupled device charge storage information, to be under the control of a synchronous signal in the implementation of a read after the transfer, charge transfer and read out the information needs of a clock control circuit and the power of three different match, the entire circuit is more complex. CMOS optical sensor by the optical converted directly from current (or voltage) signal, the signal is very easy to read.
speed
CCD charge-coupled device to be under the control of the synchronization clock to conduct unit of output information bit by bit, slow ; and CMOS optical sensor, while optical signals to electrical signals can be removed, the unit can handle both image information, the speed is much faster than the charge-coupled device CCD.
power supply and power consumption
CCD charge-coupled device most requires three power supply, power consumption is large; CMOS optical sensor using only one power supply, power consumption is very small, only charge-coupled device CCD 1 / 8 to 1 / 10, CMOS Sensor to energy conservation has great advantage.

CCD charge-coupled device image quality, production technology started early, mature technology, the use of PN junction or silicon dioxide (SiO2) isolation barrier noise, image quality has some relative advantages of CMOS optical sensors. As CMOS Optical sensor is highly integrated, the photoelectric sensor, the distance between the circuit very close to each other optical, electrical and magnetic interference is more serious and significant impact of noise on image quality, the CMOS optical sensors for a long time can not enter the utility . In recent years, with the CMOS circuit noise cancellation technology continues to evolve, for the production of high-density high-quality CMOS image sensor provides a good condition.
In addition, CCD and CMOS sensors in both the external structure zone. photodiodes to light (photons) into charge (electrons), aggregation number of electrons and light intensity is proportional to. In reading the charges, each row of data is moved to the vertical charge transfer direction of the buffer are. per line The charge information is read out continuously, and through the charge / voltage converter and amplifier sensing. This structure produces an image with low noise, high-performance features. But the production requires the use of CCD clock signals, bias technology, so the whole structure complex, increasing the power consumption, also increased the cost.
CMOS sensors around the electronic device, such as digital logic circuits, clock drivers and analog / digital converter, etc., can be integrated in the same processing procedure. CMOS sensor construction is as a memory, each image point contains a photodiode, a charge / voltage conversion unit, a re-setting and select transistor, and an amplifier, covering the entire sensor is the metal interconnect devices (applications and read timing signals ) and the vertical arrangement of the output signal interconnect device, it can simply read the signal XY addressing technique.
external structure (the application of sensors in the product structure)
CCD charge-coupled devices need to synchronize the clock under the control of behavioral output unit bit by bit, slow; and CMOS optical sensor, while optical signals to electrical signals can be removed, the unit can handle both image information, speed, faster than the charge-coupled device CCD a lot.
CMOS processing photoelectric sensor manufacturers of integrated circuits using semiconductor processes, digital cameras can be integrated into a single chip all the components, such as a photosensitive element, the image signal amplifier, the signal read circuit, ADC, image signal processor and controller, can be integrated into a single chip, also has the additional advantage of DRAM. only one chip can achieve a lot of features, so optical chips using CMOS image conversion system, the overall cost is very low. < br> What is a digital camera CCD chips are
all analog components, but when the image data into the computer Shique is a digital signal. If the data is in the camera, capture card to complete two digital, this camera is to simulate camera. The digital camera is done internally in the digital camera, so images can reduce the noise. Compared with the analog camera, digital camera, camera significantly improved signal to noise ratio, an increase of the dynamic camera range, maximum range of gray. the vast majority of research-grade CCD / CMOS chips are from the Kodak, Sony, SIT produced.
CCD and COMS classification
CCD and CMOS imaging process according to divided into two categories: dynamic (fast scan) and static (slow scan); by different applications can be divided into professional and civil level. common video chat camera (such as Logitech) and were used in a variety of digital cameras civilian level dynamic and static CCD / CMOS.
CCD imaging principle
CCD imaging process is like this: CCD photosensitive surface coating of silicon photonic components generated after capturing light electrons, the e-savings in the CCD was first below the insulation layer,bailey UGG boots, and then by the control circuit to the serial number of ways to export to the circuit module, and then through the DSP and other imaging circuit form the image. fast scan and slow scan biggest difference is the speed of light electrons and export systems and circuit different. fast scan frequency of very fast electronic export in order to achieve the level of the video refresh rate, but this will lead to electron loss, increased noise, light electrons is not completely empty; and slow scan, in contrast, focuses on circuit design protection photoelectron savings, the export rate is not high, but to ensure that the process came down to a very small electron loss and loss of its sensitivity and high dynamic range ADC to ensure that the signal conversion process is not distorted, while To reduce the noise generated by thermal effects, the general use Cooling system cooling.
read the above explanation we can know with professional-grade research why so expensive camera, from the CCD light-sensitive layer of the material and size began to photo-electron savings, the export of electronic circuits, transmission circuits, analog to digital conversion circuit, image display circuit, Cooling circuit, every step of the professional-grade camera, the process of scientific research and commercial level are different, the cost in several times to several hundred times or more. only one purpose, professional-grade cameras can capture as complete as possible to all of the optical signal. In general, the civilian level camera or digital camera can only reflect 50% of the light signal.
evaluation of the basic indicators of CCD < br> including the pixel value, SNR, signal to noise ratio
cooling temperature (SNR)
true reflection of the camera signal to noise ratio detection. all of the CCD camera manufacturers to improve the performance of the camera all try to make the signal (which can reach full well the number of electrons) the maximum extent possible, to reduce noise.
SNR = full well electronic / noise dynamic range = e = maximum number of gray = 2bit full well in the same electronic
the CCD, reducing CCD noise, can enhance the monitoring capacity of CCD, heat, or the CCD dark current noise is the noise in the Cool CCD can be the depth of the basic cooling of the Peltier eliminated. in exposure over 5-10 seconds, CCD chip It can generate heat, no cooling device chips, camera recording time can be more than 1 hour.
CCD design, digital methods will affect the noise generated. adopted to improve the structure, optimization method, the same can reduce the noise generated.

the pixel area indicators are an important indicator of the chip. pixel area is larger, more sensitive to light. because there are more pixels in an area of electronics, produce more signal. large pixels to increase sensitivity, a small increase in the pixel resolution. to improve image quality to CCD pixels must be increased, so the CCD size of certain circumstances, increase the pixel means to reduce the pixel in the photodiode. We know that the smaller the area per pixel, the lower its photographic properties, signal to noise ratio lower, more narrow dynamic range, so this method can not indefinitely increase the resolution, so if you do not blindly increase the CCD area and improve the resolution, would lead to the deterioration of image quality. But if the increased pixel CCD At the same time to maintain the existing image quality, it must at least maintain the unit pixel area based on the increase not decrease the total area of CCD. The larger CCD is currently processing more difficult, the yield is relatively low, so costs has been cut down, this contradiction in terms for the CCD is difficult to overcome.
camera and digital camera
As mentioned above, professional camera and digital camera technology, cost, technical content, image quality differences are significant, not a level of product. specific to the practical application, a digital camera of the following main issues:
digital camera with automatic exposure function, under different light sources are not the same image on film, it is difficult qualitative, To measure the image area, light density, insisted none other than the professional camera.
digital camera can not achieve real-time preview.
in special lighting conditions, such as fluorescence, dark field imaging conditions, is difficult to guarantee quality.
gel imaging instrument in the digital camera, then if the cause electronic loss, loss, etc., so can not fully capture the signal, the results of the analysis is not very accurate