What is the relationship between dpi and resolution

dpi is one of the measurement units of resolution, used for dot matrix digital images, which means the number of sampled or displayable or output dots per inch of length. DPI is a unit of measurement for the resolution of printers, mice and other devices. It is an important standard for measuring print quality and a basic indicator for judging printer resolution. Generally speaking, the higher the DPI value, the higher the printing accuracy of the printer.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

dpi is one of the units of measurement for resolution.

DPI (Dots Per Inch) is a unit of measurement for dot matrix digital images, which refers to the number of sampled, displayable or output dots per inch of length.

DPI is a unit of measurement for the resolution of devices such as printers and mice. It is one of the main parameters to measure the printing accuracy of the printer. Generally speaking, the higher the DPI value, the higher the printing accuracy of the printer.

DPI refers to pixels per inch, which is the scanning accuracy. The lower the DPI, the lower the resolution of the scan. Due to the influence of network transmission speed, the pictures used on the web are all 72dpi. However, this parameter cannot be used for developing photos. It must be 300dpi or higher 350dpi. For example, if you want to develop a 4*6-inch photo, the scanning accuracy must be 300dpi, then the file size should be (4*300)*(6*300)=1200 pixels*1800 pixels.

#The higher the DPI value of the resolution set by the printer, the finer the printed image will be. Printers can usually adjust the resolution. For example, the resolution of a striker printer is usually 60 to 90 DPI. Inkjet printers can reach 300~720 DPI. Laser printers have 600~1200 DPI.

General monitors are 96 DPI, and the DPI number of bitmaps required for printing depends on the number of printing screen lines. Generally, 150-line printing quality requires a 350 DPI bitmap. And the D (dot) here is the pixel.

Because the color mixing method of the printer is CMYK, the color (that is, the color gamut) performance is not as abundant and vivid as the RGB color light performance of the screen, so the DPI of the printer should be greater than the PPI (Pixels Per Inch) of the monitor. pixels per inch), can achieve the same delicate picture quality as RGB on the screen.

DPI printer resolution refers to the number of dots the printer can print per inch (Dot Per Inch), that is, printing accuracy (DPI), which is a measure of print quality. An important standard and a basic indicator for judging printer resolution. The resolution of printers used by general home users and small and medium-sized office users should be at least between 300DPI and 720DPI, but the bigger the DPI indicator, the better.

Summary: The difference and connection between dpi, pixels and resolution

Pixels and resolution are mainly used for electronic pictures and displays The pixel on the device is the basic unit of image composition, that is, each image is composed of n pixels. The resolution is the number of pixels the image has in length and width. The size of each pixel is not fixed. The resolution is related. Just like a monitor, the pixels are different under different resolutions (1920x1080 has 1024x768 more pixels). The display effect of the same image under different resolutions of the monitor is not very distinguishable (note that it is not shown in the picture above). Yes, you can adjust your own monitor resolution to see the effect) Resolution can also be expressed in terms of dpi (dots per inch, the output resolution of images from printers and copiers) and ppi (pixels per inch, the resolution of electronic display screens).

Extended knowledge: The difference between ppi and dpi

ppi (pixels per inch): The sampling rate of the image (in the image , the number of pixels contained per inch)

dpi (dots per inch): printing resolution (the number of dots that can be printed per inch, that is, printing accuracy)

ppi and dpi are indeed two It’s a concept, but some things are conventional. The ppi of a picture cannot reflect the printing quality that this picture can get in a printing shop. Why don’t you go to the store and give it a try? Ask the operator what you will get if your picture is 72ppi. Most operators will be confused by this kind of printing quality. Only dpi is used in printing shops, because the pictures we take must be output into photos. For the operator, what he needs to know is the pixels of your picture and the size you need to print. These two elements constitute dpi. , so although it is not standardized, we can only use the dpi size to communicate the pictures that need to be printed.

"Getting it into Photoshop and changing it to 300ppi has no practical meaning, and it increases the size of the image." Because such a change is a modification of ppi under a fixed image size (dimension), which results in an inconsistent number of pixels in the image. The real increase will lead to the expansion of the picture size without improving the image quality (the extra pixels are calculated from the difference). The correct way is to first crop your picture according to the proportion of the size you need to enlarge. , then fix the pixels of the picture (remove the check mark in front of "Redefine pixels of the picture") and proportion, and adjust the width and height in "Document Size" to be consistent with the expansion size you want. The ppi that comes out at this time is The dpi that your picture can get at this printing size. If it is lower than 120, it means the printed effect will be poor. 120~200 means the effect is okay. 300 is the best effect. If it is greater than 300, first change the "Redefine" Check the box in front of "Picture Pixels" and then change the ppi to 300 or lower.

(Note: 300dpi is the limit of the printing machine. Pictures larger than 300dpi will not improve the photo clarity. In fact, 250 is enough. Even if you input picture files larger than 300dpi to the printing machine, the printing machine The image will also be calculated to 300dpi before enlarging it. In addition, don’t underestimate the 300dpi of the printing machine. The photo quality of the 300dpi of the printing machine is insurmountable by any printing equipment.)

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