Various resolution resolution (2)
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Most scanners currently on the market have software and hardware extensions for resolution. Some scanners only write 9600×9600 DPI, which is only the maximum resolution obtained by software interpolation, not the true optical resolution of the scanner. So for the scanner, the resolution has optical resolution (or optical resolution) and maximum resolution.
We say that the resolution of a scanner is as high as 4800 DPI (this 4800 DPI is the sum of optical resolution and software difference processing), which means that when the image is input by the scanner, 4800×4800 Pixel can be collected on the scanning plane of 1 inch 2 . The scanning area of the 1 inch 2 square is 4800 × 4800 Pixel after scanning with a resolution of 4800 DPI. When scanning an image, the higher the scanning resolution is set, the finer the generated image is, and the larger the generated image file is.
(2) printer
We say that the resolution of a printer is 360 DPI, which means that when the image is output by the printer, 360 color points representing the image output effect can be printed on each inch of printing paper. The larger the number representing the resolution of the printer, the smaller the color point that characterizes the image output, and the finer the output image.
For images with a fixed file size, the larger the resolution of the printer, the smaller the size of the printed image. The size of the printer's color point is only related to the hardware process of the printer, regardless of the resolution of the image to be output.
(3) display
We say that the resolution of a brand's display is 80 DPI, which means that the display device of the display can produce 80 spots per inch of the screen in the effective display range of the display. For example, a 14-inch display (screen length of 14 inches) with a dot pitch of O.28mm, then: display resolution = 25.3995mm / inch ÷ 0.28mm / Dot = 90DPI (1Inch=25.3995mm).
When the display is shipped from the factory, the DPI value that represents the resolution of the display is generally not indicated. Only the dot pitch is given. We can calculate the resolution of the display according to the above formula. Based on our calculated DPI value, we can infer the highest display mode that the display can support. Assume that the diagonal length of the effective display range of the 14 inch display screen is 11.5 inches. Since the display ratio of the horizontal direction and the vertical direction of the display is 4:3, the effective display range can be set to a horizontal width of 4 inches and a vertical height of 3Xinch. The mathematical Pythagorean theorem can be obtained by x=11.5÷5=2.3inch. Therefore, the effective display range width is 2.3×4=9.2inch, vertical height is 2.3 x3 = 6.8 inches. The highest display mode is approximately 800 (9.2 x 90) x 600 (6.8 x 90), in which case one pixel (Pot) is represented by a dot (Dot).
The above mainly describes the device resolution of the scanner, printer and display. Strictly speaking, the resolution of the device and the resolution of the image processed by the device are two concepts that are both connected and different. The resolution of the device is determined by the production process of the hardware device. Although the resolution of some devices can be adjusted by software, they all have a very high resolution and the user cannot make any breakthrough.
When describing and understanding device resolution. We have to rely on the resolution of the image it handles. The resolution of an image is a measure of how fine the image itself is. For images processed by scanners and printers, the resolution is the number of pixels per inch, PPI (Pixels).
Per Inch) to measure. An image used for computer video processing, representing the resolution in terms of the number of pixels that can be displayed in the horizontal and vertical directions, such as 800×600, 640×480, etc. Whether the image itself is fine is only related to the resolution of the image itself, and It is independent of the resolution of the hardware device that handles it, but the processing result of the image is fine but directly related to the resolution of the device that handles it.
2. Digital camera resolution
The resolution of a digital camera determines the size of the high-quality image that can be printed in the final image, or the size of the image displayed on a computer monitor. The resolution of the digital camera depends on the CCD in the camera (Charge Coupled Device: Charge coupled device) The number of pixels on the chip, the more pixels, the higher the resolution. It can be seen that the resolution of the digital camera is also determined by its production process. It is fixed at the factory, and the user can only select a digital camera with different resolutions, but cannot adjust the resolution of a digital camera. For a similar digital camera, the higher the resolution, the higher the camera grade, but the high-resolution camera generates a large data file, which is higher for the speed of the processed computer, the memory and hard disk capacity, and the corresponding software. Requirements.
The pixel level of the digital camera and the size of the photo that can be printed at a certain resolution can be easily calculated by the following methods: If the resolution of the color printer is NDPI, the horizontal pixel of the digital camera is M, and the maximum printable photo is M÷N. inch. For example, the resolution of the printer is 300 DPI, and the maximum size of the photo image that can be printed by the digital camera with a horizontal pixel of 3600 is 12 inches (3600 ÷ 300). Obviously, the larger the size of the digital photo to be printed, the higher the pixel level of the digital camera. The method of calculating the display size is the same as the method of printing the size.
3. Resolution in the printing field
In the field of printing, the resolution is how many network lines are arranged in equal distances per inch, ie LPI (Lines Per Inch) said. In the traditional printing plate making process, a screen is added in front of the original image during the plate making process, and the screen is composed of a grid of transparent and opaque portions. These wires are also gratings, which function to cut the anatomical image of the light. Since the light has a diffractive physical property, the light passes through the mesh line to form dots that reflect different sizes of the original image image, and these dots are halftone dots. A halftone dot does not exceed a mesh area at most. The more the network cable, the more layers of the image are displayed, and the better the image quality. Therefore, the LPI representation resolution is used in the commercial printing industry.
4. Mouse resolution
The resolution of the mouse refers to the number of points that can be detected per 1 inch of movement. The higher the resolution, the higher the quality. Previously, the resolution of the mouse was usually 100 DPI, and the current mouse resolution ranged from 200 DPI to 400 DPI. High-resolution mice are commonly used for graphics and accurate computer graphics.
5. Touch screen resolution
The resolution of the touch screen refers to dividing the screen into identifiable number of contacts. It is usually expressed in terms of the number of contacts in the horizontal and vertical directions, such as 32 x 32. Some people think that the higher the resolution of the touch screen, the better. This is not the case. When using the touch screen, it should be considered according to the specific use. The touch screen with analog technology has a high resolution of 1024×1024, which is suitable for some work like screen painting and writing (handwriting recognition). In most cases, the application of touch technology is only to let people touch the button to select the "button" of software design, it is not necessary to use such high resolution. For example, when using a touch screen on a 14-inch display, the actual size of the display area is generally 25 × 18.5 cm, and a touch screen with a resolution of 32 × 32 can divide the screen into 1024 0.78 × 0.58 cm (smaller than a cigarette) Contact. The contact of the human finger against the touch screen is much larger than the diameter of the cigarette, so such a contact is sufficient.
Third, the difference between dots (Dot) and pixels (Pixel)
The dot in the DPI and the pixel in the image resolution (Pixel) are two concepts that are easily confused. The point in the DPI can be said to be the smallest display unit of the hardware device, and the pixel can be either a point or a multi-pixel. A collection of points. When the scanner scans the image, each sample of the scanner corresponds to each pixel of the formed image, so the DPI value set during scanning is equal to the PPI value of the scanned image. Can be equal.
But in many cases, the difference between the two is quite large. For example, an image with a resolution of 1 PPI is output on a 300 DPI printer. At this time, each pixel of the image corresponds to 300×300 Dot when printed. Similar problems exist in the use of computer monitors. For example, the effective display area of a 12-inch display is about 200×160 mm. If the spot diameter of the screen is 0.31 mm, the maximum number of spots that can be displayed on the screen is 640 (200÷0.31). ) × 480 (160 ÷ 0.31), the corresponding resolution is 80 DPI.
Fourth, the role of resolution
There are many ways to represent image resolution, depending on the application. The following discussion is about the role of resolution in various situations and their relationship to each other.
1. The role of resolution in graphic design
In flat design, the resolution of an image is measured by PPI, which together with the width and height of the image determines the size and image quality of the image file. For example, an image is 8 inches wide and 6 inches high with a resolution of IOOPPI. If the size of the image file is kept constant, that is, the total number of pixels is the same, the resolution is reduced to 50 PPI, and the aspect ratio is constant. The width of the image will become l6inch and the height will become 12inch.
The two images before and after the printout change, we will find that the latter's format is four times that of the former, and the image quality has dropped a lot. So what happens to the pictures before and after the two changes are sent to the computer monitor? For example, if they are sent to a display with a display mode of 800×600, we will find that the picture size of the two pictures is the same, and the picture quality is not different. For a computer display system, the PPI value of an image is meaningless, and the total number of pixels contained in the image is used, which is another resolution method described above: horizontal direction Number of pixels × number of pixels in the vertical direction. This resolution representation also indicates the width and height of the image when it is displayed. The two pictures before and after the change of the PPI value mentioned above have a total pixel count of 800X600, so they are two images with the same resolution and the same format when displayed.
2. The role of resolution in print output
Images processed in a computer are sometimes output for printing. In most printing methods, CMYK (magenta, cyan, yellow, black) four-color inks are used to express colorful colors, but the way to print colors is different from the photo, which uses a halftone dot treatment. The method is to express the continuous tone change of the image, unlike the latter, which can directly exhibit the change of continuous tone. According to the experience of the printing industry, all LPI values on the printing have such a relationship with the PPI value of the original image, namely: PPI value = LPI value × 2 × maximum size of the printed image maximum size of the original image.
In general, only by following this formula, the original image can be better reflected in the printing. The LPI value used in printing is relatively fixed, usually 75LPI for newspaper printing and 150LPI or 175LPI for color printing. Therefore, in the case of 1:1 printing, the resolution of the original image should be 150PPI, 300PPI and 350PPI for different purposes.
In fact, most of our commonly used desktop printers use halftone dot processing. The above formulas are also applicable, but they do not use a physical screen during printing, but rely on mathematical calculations to achieve halftone dots. Processing. A halftone dot produced in these printers consists of a number of printed dots. Obviously, the more dots that make up a halftone dot, the greater the range of grayscale variations it can represent. For example, to simulate 256-level grayscale changes, you need 16 × 16 = 256 print dots to form a halftone dot.