The CCD is a chip for capturing images in a digital camera. It was originally designed for cameras. With the continuous advancement of technology, its resolution has been gradually improved, and color reproduction has become more and more realistic. Today, megapixel digital cameras have become The digital camera is the protagonist of this new stage. Two of the world's leading CCD vendors, IBM and SONY, recently released their latest megapixel (IBM, see left) and 1.4 million (SONY, for their DSC-D700) CCDs.
In order to distinguish the advantages and disadvantages of the CCD, it is necessary to know the basic principles of the CCD. Using an image metaphor to illustrate, CCD's structure is like a row of conveyor belts and full of small buckets, the light is like raindrops scattered into each bucket, each bucket is a pixel. The process of pressing the shutter to take a picture is to measure in a certain order how many "drops of light" fall into the keg during a short interval of time and record it in the file (see the figure on the right). The luminosity of each CCD of an ordinary CCD is recorded with 8 bits, that is, its scale on the keg has 8 cells, and some are 10 or even 12 bits. A 10- or 12-bit CCD can be more accurate in recording color, especially in When the light is dark. Early CCDs were interlaced. At the same time, only one row was measured for every two rows of kegs. This increased the shutter speed, but the image accuracy was greatly reduced. With the advancement of technology, people have been able to let CCD records fall into the amount of “light drops†of each “keg†within a few tens of seconds or even thousands of seconds. Therefore, new CCDs are generally progressive scans. Although CCDs have been able to achieve a resolution of 1.3 million or higher at present, this does not mean that each pixel can capture every color. In fact, the CCD itself cannot distinguish color, so in practical applications You need to use a color filter, which is generally a different color in the filter layer of the CCD device. The different color patches on the filter are arranged like a mosaic in the order of GRGB (green-red-green-blue) so that each pixel under the "mosaic" senses a different color. For example, on a 1.3 megapixel CCD, 325,000 pixels sense red, 325,000 pixels sense blue, and 650,000 pixels sense green. In a digital camera with a resolution of 12801024 using this CCD, there are 640512 red pixels, 640512 blue pixels, and 6401024 green pixels. The green pixels are a bit more because of human eye sensitivity to green and other Color is not the same. Finally, when recording an image, the true color of each pixel is the average of its mix with the surrounding pixels.
There is also another method, which is the method used by Canon's CCD (for example, the one used by its Power Shot series digital cameras). It uses another arrangement of filters, the color of which is directly coated on the surface of the CCD. , (see left) The colors are arranged in the order of CYGM (Cyan-Yellow-Green-Magenta). The final color of each pixel is also the average value of its surrounding pixels, but this algorithm is more complicated. In a digital camera using this CCD with a resolution of 12801024, there are 640 x 512 cyan pixels, 640 x 512 yellow pixels 640 x 512 green pixels, and 640 x 512 magenta pixels. Thanks to the unique CCD process, Canon developed a novel, non-destructive recording method that saves storage space, which is the CCD raw data method it used on POWER SHOTPRO 70. The value of each pixel recorded by the CCD is a 10-bit photometric value of a single color, rather than the calculated 24-bit true color value, so it saves a lot of storage space, a 1536x1024 true color image, only 1.9MB can be recorded instead of 4.5MB in TIFF format. The calculation of the color value is left to the computer to complete.
According to the above introduction, it is not difficult to understand why the level of resolution does not fully reflect the quality of the CCD. The arrangement of pixels, filter technology, and calculation methods on the top of the pixel will have a serious impact on the final image quality.
In order to distinguish the advantages and disadvantages of the CCD, it is necessary to know the basic principles of the CCD. Using an image metaphor to illustrate, CCD's structure is like a row of conveyor belts and full of small buckets, the light is like raindrops scattered into each bucket, each bucket is a pixel. The process of pressing the shutter to take a picture is to measure in a certain order how many "drops of light" fall into the keg during a short interval of time and record it in the file (see the figure on the right). The luminosity of each CCD of an ordinary CCD is recorded with 8 bits, that is, its scale on the keg has 8 cells, and some are 10 or even 12 bits. A 10- or 12-bit CCD can be more accurate in recording color, especially in When the light is dark. Early CCDs were interlaced. At the same time, only one row was measured for every two rows of kegs. This increased the shutter speed, but the image accuracy was greatly reduced. With the advancement of technology, people have been able to let CCD records fall into the amount of “light drops†of each “keg†within a few tens of seconds or even thousands of seconds. Therefore, new CCDs are generally progressive scans. Although CCDs have been able to achieve a resolution of 1.3 million or higher at present, this does not mean that each pixel can capture every color. In fact, the CCD itself cannot distinguish color, so in practical applications You need to use a color filter, which is generally a different color in the filter layer of the CCD device. The different color patches on the filter are arranged like a mosaic in the order of GRGB (green-red-green-blue) so that each pixel under the "mosaic" senses a different color. For example, on a 1.3 megapixel CCD, 325,000 pixels sense red, 325,000 pixels sense blue, and 650,000 pixels sense green. In a digital camera with a resolution of 12801024 using this CCD, there are 640512 red pixels, 640512 blue pixels, and 6401024 green pixels. The green pixels are a bit more because of human eye sensitivity to green and other Color is not the same. Finally, when recording an image, the true color of each pixel is the average of its mix with the surrounding pixels.
There is also another method, which is the method used by Canon's CCD (for example, the one used by its Power Shot series digital cameras). It uses another arrangement of filters, the color of which is directly coated on the surface of the CCD. , (see left) The colors are arranged in the order of CYGM (Cyan-Yellow-Green-Magenta). The final color of each pixel is also the average value of its surrounding pixels, but this algorithm is more complicated. In a digital camera using this CCD with a resolution of 12801024, there are 640 x 512 cyan pixels, 640 x 512 yellow pixels 640 x 512 green pixels, and 640 x 512 magenta pixels. Thanks to the unique CCD process, Canon developed a novel, non-destructive recording method that saves storage space, which is the CCD raw data method it used on POWER SHOTPRO 70. The value of each pixel recorded by the CCD is a 10-bit photometric value of a single color, rather than the calculated 24-bit true color value, so it saves a lot of storage space, a 1536x1024 true color image, only 1.9MB can be recorded instead of 4.5MB in TIFF format. The calculation of the color value is left to the computer to complete.
According to the above introduction, it is not difficult to understand why the level of resolution does not fully reflect the quality of the CCD. The arrangement of pixels, filter technology, and calculation methods on the top of the pixel will have a serious impact on the final image quality.
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