Introduction to the principle of gel imaging analysis system CCD
The gel imaging system produced by each company is similar in structure, and can be used for non chemiluminescence imaging detection and analysis of DNA/RNA/ protein and other gel electrophoresis, such as EB, Coomassie brilliant blue and silver staining. It mainly distinguishes the sensitivity and resolution of gel imaging. The quality of image to be produced depends mainly on the size and pixel of CCD. There is also a software function of imaging.
Here is an introduction to CCD
1： CCD is the abbreviation of charge coupled device. It is a kind of semiconductor imaging device, so it has the advantages of high sensitivity, anti strong light, small distortion, small volume, long life, anti vibration and so on.
(1) CCD size and image quality
The size of CCD is a hard index that affects its imaging performance. It refers to the length of the diagonal of CCD. In other words, the size of CCD determines the area of the photosensitive device. The larger the area of the photosensitive device, that is, the larger the area of CCD / CMOS, the more photons captured, the better the photosensitive performance and the lower the signal-to-noise ratio. In the case of the same pixel, the larger the area of CCD, the larger the area of a single photosensitive unit, the stronger the signal-to-noise ratio and photosensitive ability, and the better the imaging quality. On the contrary, the smaller the area of a single photosensitive unit is, the weaker its signal-to-noise ratio and photosensitive ability will be, and the image quality will deviate.
(2) Pixels of CCD
How many pixels are usually used to describe the performance of a camera? Pixel is the basic material of an image. In France, there is a painting school called stippling school. It is a method to point out millions of tiny oil colored dots on the canvas to form a painting. When you stand at a certain distance to watch stippling school's oil paintings, these color dots are mixed to form a seamless painting; The principle of digital image and dot painting school is the same, but instead of small dots, they are small color squares called pixels.
There is no absolute relationship between pixel height and size. The general intuitive idea is that the higher the pixel of CCD, the more space it needs, and the larger the area size of CCD! Compared with the current production technology, this concept is right and wrong. In fact, the pixel area and the line layout precision are the key factors affecting the size of CCD; That is to say, the more precise the manufacturing technology is, the less space the circuit needs to occupy. When the relative pixel area is fixed, the circuit can be more compact, and the purpose of further reducing the area can be achieved. Therefore, in the case of a certain pixel area, the more compact the circuit layout, the higher the pixel, the larger the CCD size, and the better the imaging quality.
2： The upper layer of CCD structure decomposition is the brightening lens, the middle layer is the color separation filter, and the lower layer is the photosensitive layer
The first layer of "brightening lens"
We know that the key of digital camera imaging is its photosensitive layer. In order to expand the daylighting rate of CCD, we must expand the light receiving area of a single pixel. But the way to improve the lighting rate is also easy to make the image quality decline. This layer of "micro lens" is equivalent to adding a pair of glasses in front of the photosensitive layer. Therefore, the sensitive area is no longer determined by the opening area of the sensor, but by the surface area of the micro lens.
The second layer is "color separation filter"
The second layer of CCD is "color separation 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 concept of two color separation methods. RGB is the three primary color separation method. Almost all the colors that can be recognized by human glasses can be composed of red, green and blue, and the three letters of RGB are red, green and blue respectively. This shows that RGB color separation method is formed through the color adjustment of these three channels. In addition, CMYK is composed of four channel colors: cyan (c), magenta (m), yellow (y) and black (k). In the printing industry, CMYK is more suitable, but its adjusted color is less than RGB.
The advantage of primary color CCD is sharp image quality and true color, but the disadvantage is noise. Therefore, you can note that the general use of primary color CCD digital camera, most of the ISO sensitivity will not exceed 400. In contrast, the complementary color CCD has a Y yellow color filter, which is more careful in color resolution, but it sacrifices the resolution of some images. In ISO value, the complementary color CCD can tolerate higher sensitivity, which can generally be set above 800
Third layer: photosensitive layer
The third layer of CCD is "photosensitive film", which is mainly responsible for converting the light source passing through the color filter layer into electronic signal, and transmitting the signal to the image processing chip to restore the image.
Traditional camera film size is 35mm, 35mm is diagonal length, 35mm film sensitive area is 36 x 24mm. If the diagonal length is close to 35mm, the larger the size of CCD / CMOS is. In SLR digital cameras, many have a CCD / CMOS size close to 35mm. For example, the nikonda D100 has a CCD / CMOS size area of 23.7 x 15.6, which is much larger than that of consumer digital cameras. The CMOS size of Canon's eos-1ds is 36 x 24mm, which reaches 35mm, so the imaging is relatively good.