1. Application of CCD and CMOS in Digital Camera
Currently, image sensor chips for digital cameras are mainly divided into two types: CCD (Charge-coupled Device) and CMOS (Complementary Metal-Oxide-Semiconductor). Both can convert light signals into electrical signals.
In the past, CCDs were the most common type of image sensor in digital cameras. It delivers high-quality images, and it also does well for applications that take still photos in low light. However, due to factors such as manufacturing process and cost, CMOS sensors have replaced most of the CCD applications in recent years.
Regardless of CCD or CMOS, basically both use (photosensitive element) silicon photodiode to convert light and electricity and then output and collect image information. But in fact, they collect image information in different ways.
2. Image Acquisition Methods of CCD and CMOS Chips
The image acquisition method of the CMOS sensor is proactive, and the charge generated by the photosensitive diode will be directly amplified and output by the transistor next to it; while the CCD sensor is a passive acquisition and an external voltage must be applied to move the charge in each pixel to the transmission channel. And this external voltage usually needs 12~18V, so CCD must also have a more precise power line design and withstand voltage strength. High driving voltage makes the power consumption of CCD much higher than that of CMOS. The power consumption of CMOS is only 1/8 to 1/10 of that of CCD.
Because of different image collection methods, higher technical requirements and lower yield rate of producing CCD chips lead to the high cost of making CCD sensors, and currently, only SONY, Philips, Kodak, Matsushita, Fuji, and Sharp can produce CCD chips Most of these manufacturers are Japanese manufacturers.
Moreover, there are many processes for the CCD sensor to collect image information:
1. The photosensitive element receives the light signal and converts it into an electrical signal, and these electrical signals are transmitted one by one at only one or several ports, under the drive of the external voltage, to the buffer;
2. When all the charge signals are in the buffer, they are guided by the bottom line and output to the amplifier (Gain Amplifiers) for amplification;
3. All the amplified electrical signals are connected in series and then sent to the ADC ( Amplification and analog-to-digital signal converter) output;
4. Acquire images and store them. The image processing process is more complex and cumbersome. This also shows that the speed of converting image information of CCD cameras is relatively slow.
In CMOS sensors, each photosensitive element in the CMOS sensor directly integrates the amplifier and analog-to-digital conversion logic. When the photosensitive diode receives light and generates an analog electrical signal, the electrical signal is first amplified by the amplifier in the photosensitive element, and then Convert directly to the corresponding digital signal. In other words, in a CMOS sensor, each photosensitive element can generate a final digital output, and the resulting digital signals are combined and sent directly to the DSP chip for processing into image information. The image processing process is simple. The conversion speed of image information of CMOS cameras is relatively fast.
3. Summary of advantages and disadvantages of CCD and CMOS chips
The characteristic of the CCD sensor is that it reads the image at a slow speed, but the working principle of the CCD is to ensure that all signals are transmitted in a consistent manner without distortion, with high integrity, high image restoration, and high quality.
The characteristic of CMOS photoreceptors is that their image-processing process is relatively simple, fast, and highly integrated. When the CMOS photosensitive element receives the light signal and converts it into a charge signal, the electrical signal is directly amplified by its own amplifier in situ, and then moved to the ADC through the BUS channel for conversion into digital data. However, it is impossible to guarantee that the amplification ratio of each charge signal remains strictly consistent, so the amplified image data cannot represent the original appearance of the subject, and numerous amplifiers will greatly increase the noise of the CMOS sensor, affecting image quality.
The main conditions for determining CMOS chips as sensors for sports cameras
However, the quality of the current CMOS sensors has been greatly improved, and the image quality of many CMOS sensors is comparable to that of CCDs.
In summary, CCD chips have many advantages over CMOS chips, such as low noise, wide dynamic range, good color reproduction, and so on. However, for sports cameras that need to quickly capture high-speed motion, CCD chips are not the best choice, but CMOS chips are more suitable for the following reasons:
1. Slow speed: The readout speed of the CCD chip is relatively slow, which cannot meet the requirements of high-speed continuous shooting.
2. High power consumption: The CCD chip needs to consume a lot of power during high-speed readout, which will cause the camera to overheat and affect the life of the camera and user experience.
3. Easy to produce afterimages: Due to the readout method of the CCD chip, it is easy to produce afterimages in high-speed motion scenes, which affects the quality of photos.
In contrast, CMOS chips have the advantages of high-speed readout, low power consumption, and low noise, which can meet the needs of high-speed motion shooting. Therefore, most action cameras use CMOS chips to achieve high-speed continuous shooting and high-quality photos and videos.