The gel imaging produced by each company is similar in structure, and can be used for non-chemiluminescence imaging such as DNA/RNA/protein gel electrophoresis (such as EB, Coomassie blue, silver staining). Detection and analysis, mainly to distinguish the sensitivity and resolution of gel imaging, the quality of the image to be taken is mainly depends on the size of the CCD, pixels, and a software function of imaging.
Introduction to CCD:
One: CCD is the abbreviation of Charge Coupled Device. It is a kind of semiconductor imaging device, which has the advantages of high sensitivity, strong glare, small distortion, small volume, long life and vibration resistance.
(1) CCD size and image quality
The CCD size is a hard indicator that affects its imaging performance. It refers to the length of the diagonal of the CCD. That is to say, the size of the CCD determines the size of the photosensitive device. The larger the area of ​​the photosensitive device, that is, the larger the CCD/CMOS area, the more photons are captured, the better the photographic performance, and the lower the signal-to-noise ratio. In the case of the same pixel, the larger the area of ​​the CCD, the larger the area of ​​a single photosensitive unit, and the stronger the signal-to-noise ratio and the photographic ability, the better the image quality. Conversely, the smaller the area of ​​a single photosensitive unit, the weaker its signal-to-noise ratio and sensitivity, and the quality of the image will be deviated.
(2) CCD pixels
Usually, how many pixels are used to describe the performance of the camera. The pixel is generally understood to be the basic material of the image. In France, there is a painting called the point color, which is to point out millions of small oil color points on the canvas. The method of composing the paintings, when you stand at a certain distance to see the oil paintings of the dot painting, these color points are mixed to form a seamless painting; the digital image is the same as the principle of the dot painting school, but instead of small The dots are colored small squares called pixels.
There is no absolute relationship between the pixel level and the size. Generally speaking, the higher the pixel of the CCD, the more space it needs, and the larger the area size of the CCD should be. Compared with the current production technology, this concept is correct and wrong. In fact, the pixel area size and the fineness of the line layout are the key factors affecting the size of the CCD; that is, the more precise the manufacturing technique, the smaller the space required for the line, and the relative pixel area can be fixed. Closer, you can achieve the purpose of further reducing the area, so in the case of a certain pixel area, the tighter the line layout, the higher the pixel, the larger the CCD size, the better the image quality.
Two: CCD structure decomposition upper layer is the brightness enhancement lens, the middle layer is the color separation filter, the lower layer is the photosensitive layer
The first layer of "enhanced lens"
We know that the key to digital camera imaging lies in its photosensitive layer. In order to expand the CCD's luminous rate, it is necessary to extend the light receiving area of ​​a single pixel. However, the method of increasing the daylighting rate is also likely to degrade the image quality. This layer of "micro lens" 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 is determined by the surface area of ​​the microlens.
The second layer is the "separation filter"
The second layer of the CCD is a "separation color filter". There are currently two color separation methods, one is the RGB primary color separation method, and the other is the CMYK complementary color separation method. First of all, let us first understand the concept of two color separation methods, RGB is the three primary color separation method, almost all the colors that human glasses can recognize, can be composed of red, green and blue, and the three letters of RGB are Red. Green and Blue, which means that the RGB color separation method is adjusted by the color of these three channels. Let's talk about CMYK, which is made up of the colors of four channels. They are 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 the primary color CCD is that the picture quality is sharp and the color is real, but the disadvantage is the noise problem. Therefore, you can note that digital cameras that use primary color CCDs generally do not exceed 400 in ISO sensitivity. In contrast, the complementary color CCD has a Y yellow color filter, which is more careful in color resolution, but sacrifices the resolution of some images. On the ISO value, the complementary color CCD can tolerate higher sensitivity, generally Can be set above 800
Third layer: photosensitive layer
The third layer of the CCD is a "photosensitive sheet". This layer is mainly responsible for converting the light source that passes through the filter color layer into an electronic signal, and transmits the signal to the image processing chip to restore the image.
The conventional camera film size is 35mm, 35mm is the diagonal length, and the 35mm film has a photosensitive area of ​​36 x 24mm. Converted to a digital camera, the diagonal length is approximately 35mm, and the CCD/CMOS size is larger. In SLR digital cameras, many have CCD/CMOS sizes close to 35mm, such as the Nikon D100. The CCD/CMOS size is 23.7 x 15.6, which is much larger than the consumer digital camera, and Canon's EOS-1Ds CMOS. The size is 36 x 24mm, which is 35mm, so the imaging is relatively good.
Comparison and difference between CCD and CMOS
The main difference between CCD and CMOS in manufacturing is that CCD is integrated on semiconductor single crystal material, and CMOS is integrated on semiconductor material called metal oxide. There is no essential difference in working principle. CCD only has a few manufacturers such as Sony and Panasonic to master this technology. Moreover, the CCD manufacturing process is more complicated, and the price of the camera using the CCD will be relatively expensive. In fact, after the technical transformation, the gap between the actual effects of CCD and CMOS has been reduced a lot. Moreover, the manufacturing cost and power consumption of CMOS are lower than that of CCD, so many CMOS sensors used by camera manufacturers. Imaging: The imaging transparency and sharpness of the CCD are very good under the same pixel, and the color reproduction and exposure can be basically accurate. The products of CMOS are generally transparent, the color reproduction ability of the object is weak, and the exposure is not very good. Due to its physical characteristics, the imaging quality of CMOS and the CCD still have a certain distance. However, due to its low price and high integration, it has been widely used in the field of cameras.
The difference between CCD and CMOS:
CCD is a relatively mature imaging device, and CMOS is regarded as a future imaging device.
Since the CMOS structure is relatively simple, it is the same as the existing large-scale integrated circuit production process, so that the production cost can be reduced. In principle, the CMOS signal is a charge signal in points, and the CCD is a current signal in the unit of action. The former is more sensitive, the speed is faster, and the power is saved. Now advanced CMOS is not worse than the general CCD, but the CMOS process is not very mature. Ordinary SMOS generally has low resolution and poor imaging.
The current situation is that many low-end entry-level digital cameras use inexpensive low-end CMOS chips, and the image quality is poor. Popular, advanced and professional digital cameras use different grades of CCDs, and individual professional or quasi-professional digital cameras use advanced CMOS chips. The X3 chip, which represents the future development of imaging technology, is actually a CMOS chip.
CCD and CMOS are not good or bad, but in general, the quality of imaging using CCD chips in popular digital cameras is better.
2CCD's dead pixels and repair problems
When shooting night scenes or when covering the lens cover for a long time, the color points on the image are not necessarily CCD dead spots, some are noise, and the CCD temperature will be improved after the temperature is lowered. Some firmware upgrades can also be improved.
If the CCD really has a bad point, it can be said that it cannot be repaired. Because it is a hardware problem of the CCD, it is almost impossible to repair an imaging unit of the CCD, and it is also uneconomical. Only change the camera or change the CCD.
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