Clear resolution

Resolution is an important concept related to image processing. It is a technical parameter to measure the ability of detail representation of an image. However, there are many ways to represent resolution, and their meaning varies. Therefore, it is necessary to correctly understand the specific meaning of resolution in various situations and to clarify the relationship between different representation methods. This article focuses on a brief introduction to the resolution of several common image input/output devices, and then describes the characteristics and relationships of different resolutions of the image, input/output of images on different resolution image input/output devices.

First, a few concepts about the resolution To accurately understand and understand the meaning of resolution, it is necessary to make clear the following concepts. Resolution: Includes device resolution, screen resolution, graphic resolution, scan resolution, and bit resolution.

Device Resolution: Also known as output resolution, refers to the number of dots per inch that can be produced by various types of output devices, such as the resolution of displays, inkjet printers, laser printers, thermal wax printers, and plotters. This resolution is measured in units of DPI. Generally, PC monitors have device resolutions between 60 and 120 DPI. The print device resolution is between 180 and 720 DPI.

Screen Resolution: Also known as the screen resolution, refers to the number of dots per inch on the screen used to print grayscale graphics or color separations. This resolution is scaled by the number of lines per inch (RPI).

Image Resolution: Refers to the amount of information stored in the graphic. There are many ways to measure this resolution, typically measured in pixels per inch (PPI). The resolution of the graphics and the size of the graphics together determine the size of the file and the quality of the output. The larger the value, the more disk space the graphics file occupies. The resolution of the graphic affects the size of the file in a proportional relationship, ie the file size is proportional to the square of its graphic resolution. If you keep the size of the graphics unchanged and double its graphics resolution, the file size will increase by a factor of four. The graphics resolution also affects the size of the graphics on the screen. If you increase the graphics resolution from 72 PPI to 144 PPI (keep the graphics size unchanged) on a monitor with a device resolution of 72 DPI, the graphics will be displayed on the screen at twice the actual size of the original graphics.

Scan resolution: The resolution determined before scanning a graphic. It will affect the quality and performance of the generated graphic file. It determines how the graphic will be displayed or printed. If the scanning pattern is used for a 640×480 pixel screen display, the scanning resolution does not have to be greater than the device resolution of a typical display screen, ie generally not exceeding 120 DPI. However, in most cases, the scanning pattern is prepared for later output in a high-resolution device. If the resolution of the graphics scan is too low, graphics processing software may use the color values ​​of a single pixel to create some halftone dots, which can result in rough output. Conversely, if the scanning resolution is too high, the digital graphics will produce more information than needed for printing, which not only slows down the printing speed, but also causes a slight transition of the graphical hue when the printout is output. In general, the print resolution, scan, and output image size should be used to calculate the correct scan resolution. Multiply the maximum size of the output graphic by the screen resolution, and then multiply by the ratio of screen lines (usually 2:1) to get the total number of pixels required for the graphic. The optimum scanning resolution is obtained by dividing the total number of pixels by the maximum size of the scanning pattern, that is, the pattern scanning resolution=(the maximum size of the output pattern×the screen resolution×the ratio of the screen lines)/the maximum size of the scanning pattern.

Bit Resolution: Also known as bit depth, it is used to measure the number of bits of information stored in each pixel. This resolution determines how many colors can be displayed on the screen at a time, typically 8 bits, 24 bits, or 32 bits. Sometimes we also refer to bit resolution as color depth.

Second, the resolution of several types of image input/output devices The resolution of scanners, printers, fax machines, monitors, digital cameras, projectors, televisions, commercial printers, and other input/output devices and pointing devices such as mice and touch screens have their own respective resolutions. The meaning of it, clarifying its meaning, is conducive to our purchase and use of these devices. The reader must note that the resolution mentioned here refers to the device resolution.
1. Scanners, printers, fax machines, and display resolutions For hardware devices such as scanners, printers, fax machines, and displays, the resolution is measured in dots per inch (DPI). The resolution of the scanner is determined from three aspects: the optical part, the hardware part and the software part. That is, the resolution of the scanner is equal to the resolution of its optical components plus its own resolution obtained through hardware and software processing and analysis. The optical resolution is the actual number of light spots that can be captured by the scanner's optics within the area per square inch. It refers to the physical resolution of the scanner CCD and the true resolution of the scanner. Its value is determined by the CCD. The number of pixels divided by the scanner's horizontal maximum scan size. Resolution of 1200DPI scanner, the optical part of the resolution only accounts for 400 ~ 600DPI. The resolution of the extended part (generated by hardware and software) is generated by computer analysis of the image and scientific filling of the blank part (this process is also called interpolation processing). Optical scanning and output are one-to-one, what is scanned and what is output. After the computer hardware and software processing, the output image will become more realistic and the resolution will be higher. Most scanners currently on the market have software and hardware extensions to the resolution. Some scanner ads only write 9600×9600 DPI, which is the maximum resolution obtained by software interpolation, not the actual optical resolution of the scanner. So for the scanner, its resolution has optical resolution (or optical resolution) and maximum resolution.

We say that a scanner has a resolution of up to 4800 DPI (this 4800 DPI is the sum of the optical resolution and software differential processing), which means that when the image is input by the scanner, 4800× can be acquired on a 1 inch square scan frame. 4800 pixels (ixel). Scan area of ​​1 inch square, scanned with a resolution of 4800 DPI produces an image size of 4800 pixels x 4800 pixels. When scanning an image, the higher the scanning resolution is set, the finer the effect of the generated image, and the larger the generated image file. We say that the resolution of a certain printer is 360 DPI, which means that when using the printer to output images, 360 color dots representing the output of images 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 output of the image, and the finer the effect of the output image. For a fixed-size image, the larger the printer resolution, the smaller the printed image size. The size of the printer's color point is only related to the printer's hardware process, regardless of the resolution of the image being output.
The facsimile has both scanning (before sending) and printing (post-reception) functions, and you can refer to the relevant parts of the meanings of the scanner and the printer resolution when understanding the resolution. We say that the resolution of a certain brand of display is 80 DPI, which means that within the effective display range of the display, the display's imaging device can produce 80 spots on each inch of the screen. For example, for a 14-inch display (with a screen diagonal of 14 inches) with a pitch of 0.28 mm, then: Display resolution = 25.35995 mm/inch ÷ 0.28 mm/Dot ≈ 90 DPI (1 inch =25.3995mm). The DPI value that represents the resolution of the display is generally not displayed when the display is shipped from the factory. Only the dot pitch is given. We can calculate the resolution of the display according to the above formula. Based on the DPI value we calculated, we can then calculate the maximum display mode that the monitor can support. Assume that the diagonal length of the effective display range of the 14-inch display screen is 11.5 inches. Since the horizontal and vertical display ratio of the display is 4:3, the horizontal width of the effective display range is 4X inches and the vertical height is 3X. Inches, according to the mathematical Pythagorean theorem, X = 11.5 ÷ 5 = 2.3 inches. So the effective display range width is 2.3 x 4 = 9.2 inches and the vertical height is 2.3 x 3 = 6.8 inches. The maximum display mode is approximately: 800 (9.2 × 90) × 600 (6.8 × 90). In this case, one dot is used to represent one pixel.

The above mainly describes the device resolution of scanners, printers, fax machines and displays. Strictly speaking, the resolution of the device and the resolution of the image processed by the device are two related and different concepts. The device resolution 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 limited maximum resolution, and the user cannot make any breakthrough on it. In describing and understanding the device resolution, we must rely on the resolution of the image it processes. The resolution of the image is a measure of the fineness of the image itself. For images processed by scanners, printers, and fax machines, the resolution is measured in pixels per inch, or PPI (Pixels Per Inch). For computer-processed images, the resolution is represented by the number of pixels that can be displayed in the horizontal and vertical directions, such as 800 x 600, 640 x 480, and so on. Whether the image itself is fine depends only on the resolution of the image itself, but not on the resolution of the hardware device processing it, but whether the result of the image processing is fine is directly related to the resolution of the device processing it. For example, a 90 PPI image is finer. If you print it on a 40 DPI printer, the print effect is quite bad. For the scanner, the resolution is proportional to the fineness of the generated image, but its resolution can only give an initial value for the image resolution (the value of the DPI of the PPI value and the resolution of the scanner is Equally, there is no restriction on the resolution of the image. We can use software to arbitrarily adjust the resolution of the scanned image (as shown in Figure 1 and Figure 2). In addition, it should be noted that we usually say a 640×480 image, which is the size of the image, which does not include the meaning of image resolution.

2. The resolution of a digital camera The resolution of a digital camera determines the size of the high-quality picture that the captured image can ultimately print, or the size of the picture that can be displayed on a computer monitor. The resolution of a digital camera depends on the number of pixels on the CCD (Charge Coupled Device) chip in the camera. The more pixels, the higher the resolution. It can be seen that the resolution of a digital camera is determined by its production process, and it is fixed at the factory. Users can only select digital cameras with different resolutions, but they cannot adjust the resolution of a digital camera. For a digital camera of the same type, the higher the resolution, the higher the camera grade, but the high-resolution camera generates a large data file, which is comparable to the speed, memory, hard disk capacity, and corresponding software of the processed and processed computer. High demand. The level of the pixel level of the digital camera and the size of the photo that can be printed at a certain resolution can be calculated simply by the following method: if the resolution of the color printer is N DPI , the horizontal pixel of the digital camera is M, and the maximum printable picture is M. N inches. For example, a printer with a resolution of 300 DPI and a digital camera with a horizontal pixel of 3600 can print an image with a maximum size of 12 inches (3,600÷300) without interpolation. Obviously, the larger the size of digital photos to be printed, the more digital cameras with higher pixel levels are required. The method of calculating the display size is the same as the method of printing the size.

3. Projector resolution &n