Basic knowledge-knowledge of various resolutions from http://vod.sjtu.edu.cn/help/Article_Show.asp? ArticleID = 308

Preface

Resolution is an important concept related to images. It is a technical parameter for measuring the expressiveness of image details. However, there are many types of resolutions with different meanings. Correct understanding of the specific meaning of resolution in various situations, and clarifying the relationship between different representation methods is a crucial step. The following describes several common image input/output resolutions and different image input/output device resolutions for your reference.

PPI, DPI, LPI, and depth

Image resolution (PPI)
Imageresolution: the amount of information stored in the image. This resolution can be measured in multiple ways, typically by the number of pixels per inch (PPI. The value of image resolution and image size (height and width) determines the file size and output quality. The larger the value, the larger the disk space occupied by the image file.
The image resolution affects the file size proportionally, that is, the file size is proportional to the square of the image resolution. If the image size remains unchanged and the image resolution is doubled, the file size is increased to four times the original size.

Scan resolution (DPI)
Scan resolution: the resolution set before scanning an image. It affects the quality and performance of the generated image file. It determines the way in which the image will be displayed or printed. If the scanned image is used for Screen Display of 640x480 pixels, the scanning resolution does not need to be greater than the device resolution of the general display screen, that is, the scanning resolution generally does not exceed 120 DPI.
However, in most cases, scanned images are output in High-Resolution devices. If the image scan resolution is too low, the output will be very rough. If the scanning resolution is too high, the digital image will generate information that exceeds the printing requirement, which not only slows down the printing speed, but also will cause the slight transition of the image tone to be lost when printing the output. In general, the image resolution should be twice the screen resolution, which is the standard adopted by most output centers and printing plants in China. However, in fact, the image resolution should be 1.5 times the screen frequency. I am afraid there will be controversy about this issue, and the specific situations of different images are indeed different. For more information, see screen angle and output resolution.

Screen Resolution (LPI)
Screen Resolution (screenresolution): Also known as screen frequency (printing term), refers to the number of network cables per inch (that is, the number of mounted Network cables) of the screen used for printing images, with (LPI). For example, 150lpi adds 150 Network cables per inch.

Bit resolution (BIT) of an image)
Bitresolution: This is also called bitdepth. It is used to measure the number of bits in each pixel. This resolution determines how many color levels can be marked. Generally, there are 8-bit, 16-bit, 24-bit, or 32-bit colors. Sometimes we call bit resolution color depth. The so-called "bits" actually refers to the square number of "2". 8 bits are the eight power of 2, that is, 8 bits are multiplied by 2, which is equal to 256. Therefore, an 8-bit color depth image shows a color level of 256.

Device resolution (DPI)
Deviceresolution: Also known as the output resolution, refers to the number of points that can be generated on various output devices per inch, such as the display, inkjet printer, laser printer, and plotter resolution. This resolution is measured by DPI. Currently, the device resolution of a PC display is between 60 and DPI. The resolution of the printing device is between 360 and 1440dpi.

Resolution of scanners, printers, and displays

For hardware devices such as scanners, printers, and monitors, the resolution is measured by the number of dots per inch, namely, the DPI (dots per inch.
The resolution of a scanner must be determined in three aspects: Optical, hardware, and software. That is to say, the resolution of the scanner is equal to the resolution of its optical component plus the resolution obtained by processing and analyzing it through hardware and software. The optical resolution is the actual number of points of light that can be captured by the optical components of the scanner within each square inch. It refers to the physical resolution of the CCD and the real resolution of the scanner, the value is calculated by dividing the pixels of CCD by the maximum horizontal size of the scanner. The resolution of the optical part is only 400 ~ 600 dpi. The resolution of the extended part is produced by scientifically filling the blank part through computer analysis of the image (generated by hardware and software, this process is also called "interpolation ). Optical Scanning and output are one-to-one. What is scanned and what is output. After computer software and hardware processing, the output image will become more realistic and the resolution will be higher. Most of the scanners currently on the market have resolution-specific software and hardware expansion functions. Some scanner advertisements write 9600 × 9600 DPI, which is only the maximum resolution obtained by the software "interpolation", not the true optical resolution of the scanner. Therefore, for scanners, the resolution is 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), that is, when a scanner is used to input an image, you can set up to 4800x4800 pixels (pixel) on a 1 square inch scanned image ). The image size generated after scanning with a resolution of 1 inch DPI is 800 pixel × 4800 pixel. When you scan an image, the higher the Resolution, the more precise the generated image, the larger the generated image file, but the more interpolation components.
We say that the resolution of a printer is 360 DPI, which means that when the printer is used to output an image, 360 color points can be printed on the printing paper per inch to characterize the image output effect. The larger the number of printer resolutions, the smaller the color point of the image output, and the finer the output image. The size of the printer's color points is only related to the printer's Hardware process, but not to the resolution of the image to be output.
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 equipment can produce 80 bits per inch on the screen. For example, if a 14 inch-inch display (with a diagonal line length of 14 inch) is located at a distance of 0.28mm, the display resolution is 25.3995mm/inch large. 28mm/DOT ≈ 90 dpi (1 inch = 25.3995mm ). When the monitor leaves the factory, the DPI value indicating the resolution of the monitor is generally not marked. Only the dot distance is given, and the resolution of the monitor can be calculated based on the above formula. Based on the calculated DPI value, we can then calculate the maximum Display Mode Supported by the display. Assume that the diagonal line length of the valid display range of the 14 inch display is 11.5 inch, because the horizontal and vertical display ratio of the display is 4: 3, the horizontal width of the valid display range is 4, the vertical height is 3 inches. According to the math theorem, x = 11.5 ÷ 5 = 2.3 inch is obtained. Therefore, the valid display range is 2.3x4 = 9.2 inch, and the vertical height is 2.3x3 = 6.8 inch. The maximum display mode is about 800 (9.2 × 90) × 600 (6.8 × 90). A dot is used to represent a pixel ).
The above mainly describes the device resolutions of scanners, printers and monitors.
Note: The device resolution and the resolution of the image processed by the device are two concepts that have both links and differences.
The device resolution is determined by the hardware production process. Although the resolution of some devices can be adjusted through software, they all have a limited maximum resolution, users cannot make any breakthroughs in it. For images processed by scanners and printers, the resolution is measured by the number of pixels per inch, namely, the pixelsperinch. Images used for Computer Video Processing represent resolutions in the horizontal and vertical directions, such as 800 × 600, 640 × 480, and so on.
The resolution of an image is a measure of the precision of the image. Whether the image itself is fine depends only on the resolution of the image itself, but not on the resolution of the hardware device that processes the image, however, whether the image processing result is accurate is directly related to the resolution of the device that processes the image. For example, a 90ppi image is relatively fine. If it is printed on a printer with a resolution of 40 dpi, the print effect is also quite bad. For scanners, the resolution is proportional to the precision of the generated image, however, the resolution can only give an initial value for the image resolution (this PPI value is the same as the DPI setting value for the scanner's resolution) and does not limit the resolution of the image, we can use the software to adjust the resolution of the images generated by the scan. In addition, it should be noted that we usually refer to an image of 640x480, which is about the image size, excluding the meaning of the image resolution.

About the resolution of a digital camera

The resolution of a digital camera determines the final size of the image to be taken, or the size of the image to be displayed on a computer display. The resolution of a digital camera depends on the number of pixels on the CCD (chargecoupleddevice: Charge coupler) chip in the camera. The more pixels, the higher the resolution. The resolution of a digital camera is also determined by its production process. It is fixed at the time of factory delivery. Users can only choose a digital camera with different resolutions, but cannot adjust the resolution of a digital camera. For similar digital cameras, the higher the Resolution, the higher the camera grade, but the data files generated by high-resolution cameras are large, high requirements on the speed, memory, hard disk capacity, and corresponding software of the computer to be processed and processed.

Pixels in device space are generally not equivalent to points. A point is about 1/72 inch. Only when the resolution of the display device is 72 dpi and the scaling factor is 1.0, the pixels and points are roughly consistent.