Resolution Details

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　Resolution is an important concept related to image processing. It is a technical parameter that measures the ability to express image details. However, there are many ways to express resolution, and their meanings are also

different. Therefore, it is necessary to correctly understand the specific meaning of resolution in various situations and clarify the relationship between different expression methods. This article focuses on briefly

introducing the resolution of several common image input/output devices, and then introduces

the characteristics and relationship of images with different resolutions when input/output images on image input/output devices with different resolutions.

　　1. Several concepts about resolution

　　To accurately grasp and understand the meaning of resolution, it is necessary to clarify the following concepts. Resolution: includes device resolution, screen resolution

, graphic resolution, scanning resolution and bit resolution.

　　Device resolution: also known as output resolution, refers to the number of dots that can be produced per inch on various output devices, such as

the resolution of monitors, inkjet printers, laser printers, thermal wax printers, and plotters. This resolution is measured by the unit of DPI. Generally speaking, the device resolution of PC monitors is

between 60 and 120DPI. The resolution of printing devices is between 180 and 720DPI.

　　Screen Resolution: Also known as screen frequency, it refers to the number of dots per inch on the screen used to print grayscale graphics or color separations. This

resolution is calibrated by the number of lines per inch (RPI).

　　Image Resolution: It refers to the amount of information stored in a graphic. There are many ways to measure this resolution, typically measured in pixels per inch

(PPI). The image resolution and the image size value together determine the file size and output quality. The larger the value, the more disk space the image file occupies. Image

resolution affects the file size in a proportional relationship, that is, the file size is proportional to the square of its image resolution. If the image size remains unchanged and its image resolution is doubled

, its file size will increase by four times. Image resolution also affects the size of the image displayed on the screen. If the

image resolution is increased from 72PPI to 144PPI on a device with a resolution of 72DPI (keeping the image size unchanged), the image will be displayed on the screen at twice the actual size of the original image.

　　Scanning resolution: refers to the resolution determined before scanning a graphic. It will affect the quality and performance of the generated graphic file, and it determines how the graphic will

be displayed or printed. If the scanned graphic is used for a 640×480 pixel screen display, the scanning resolution does not need to be greater than the device resolution of the general monitor screen, that is, generally not more than

120DPI. But in most cases, the scanned graphics are prepared for later output in high-resolution devices. If the graphics scanning resolution is too low, the graphics processing software may

use the color value of a single pixel to create some halftone dots, which will result in a rough output effect. Conversely, if the scanning resolution is too high, the digital graphics will produce more

information than is needed for printing, which will not only slow down the printing speed, but also cause the subtle transition of the graphic tone to be lost when printed out. In general,

the screen resolution of the printout, the scanned and output graphic size should be used to calculate the correct scanning resolution.

　　Multiply the maximum size of the output graphic by the screen resolution, and then multiply it by the screen ratio (usually 2:1) to get the total number of pixels required for the graphic. The optimal scanning resolution is obtained by dividing the total number of pixels by

the maximum size of the scanned graphics, that is: Graphic scanning resolution = (maximum size of output graphics × screen resolution × screen ratio) / maximum

size of scanned graphics.

　　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. The most common ones are 8-bit, 24-bit or 32-bit colors. Sometimes we also call bit resolution color depth.

　　2. Resolution of several image input/output devices The resolution

　　of input/output devices such as scanners, printers, fax machines, monitors, digital cameras, projectors, televisions, commercial printing, and pointing devices such as mice and touch screens

has its own meaning.