What is "CCD" in photography?

When it comes to the size of CCD, it actually refers to the area of photosensitive devices, including CCD and CMOS. The larger the area of photosensitive device, the larger the CCD/CMOS area, the more photons captured, the better the photosensitive performance and the lower the signal-to-noise ratio. CCD/CMOS is an element used for photosensitive imaging in digital cameras, which is equivalent to the film in traditional optical cameras.

The surface of photosensitive elements on CCD has the ability to store charges and is arranged in a matrix. When its surface feels the light, it will reflect the charge to the components, and the signals generated by all the photosensitive components on the whole CCD constitute a complete picture.

If you decompose CCD, you will find that the structure of CCD has three layers, the first layer is "microlens", the second layer is "dichroic filter" and the third layer is "photosensitive layer".

The first layer of "microlens"

We know that the key to digital camera imaging lies in its photosensitive layer. In order to expand the lighting rate of CCD, it is necessary to expand the light receiving area of a single pixel. However, the method of improving the lighting rate is also easy to reduce the image quality. This layer of "microlens" is equivalent to adding a pair of glasses in front of the photosensitive layer. Therefore, the photosensitive area is no longer determined by the opening area of the sensor, but by the surface area of the microlens.

The second layer is a "dichroic filter"

The second layer of CCD is the "dichroic filter". At present, there are two color separation methods, one is RGB primary color separation method, the other is CMYK complementary color separation method. These two methods have their own advantages and disadvantages. First of all, let's understand the concepts of two color separation methods. RGB is a method for separating three primary colors. Almost all the colors that human glasses can recognize can be composed of red, green and blue. The three letters of RGB are red, green and blue respectively, which shows that RGB color separation is formed by adjusting the colors of these three channels. Let's talk about CMYK, which is composed of four channels of colors, namely cyan (C), magenta (M), yellow (Y) and black (K). In the printing industry, CMYK is more suitable, but its adjusted color is not as much as RGB.

The advantage of primary color CCD is sharp image quality and true color, but the disadvantage is noise. Therefore, we can notice that the ISO sensitivity of digital cameras that generally use primary color CCD will not exceed 400. In contrast, complementary color CCD has a Y-yellow color filter, which pays more attention to color resolution, but sacrifices the resolution of some images. On the ISO value, complementary color CCD can tolerate higher sensitivity, which can generally be set above 800.

The third layer: photosensitive layer

The third layer of CCD is the "photosensitive plate", which is mainly responsible for converting the light source of the filtered color layer into an electrical signal and transmitting the signal to the image processing chip to restore the image.

The film size of the traditional camera is 35mm, the diagonal length is 35mm, and the photosensitive area of the 35mm film is 36 x 24mm. When converted into a digital camera, the diagonal length is about 35mm, and the larger the CCD/CMOS size is. In SLR digital cameras, many have CCD/CMOS dimensions close to 35mm. For example, Nikon D 100, CCD/CMOS size area reaches 23.7 x 15.6, which is much larger than consumer digital cameras, while Canon EOS- 1Ds CMOS size is 36 x 24mm, reaching an area of 35mm, so the imaging is relatively good.

There are four kinds of consumer digital cameras in the market: 2/3 inch,11.8 inch, 1/2.7 inch, 1/3.2 inch. The larger the CCD/CMOS size, the larger the photosensitive area and the better the imaging effect. 11.8-inch 3-megapixel camera is usually better than 1/2.7-inch 4-megapixel camera (the light-sensitive area of the latter is only 55% of the former). The increase of CCD/CMOS pixels with the same size is a good thing, but it will also lead to the decrease of the photosensitive area of a single pixel, which may lead to underexposure. However, in order to increase the number of CCD/CMOS pixels while maintaining the existing image quality, it is necessary to increase the total area of CCD/CMOS on the basis of at least maintaining the area of a single pixel. At present, it is difficult to manufacture larger CCD/CMOS, and the cost is very high. Therefore, the larger the CCD/CMOS size, the more expensive the digital camera is. The size of the photosensitive device directly affects the volume and weight of the digital camera. The CCD/CMOS size of ultra-thin and ultra-light digital cameras is generally relatively small. The more professional digital cameras are, the larger the CCD/CMOS size is.