What Are Pixels Per Inch?

It describes the number of pixels contained in an image per inch of distance in the horizontal and vertical directions.

Pixels per inch

Right!

It describes the number of pixels contained in an image per inch of distance in the horizontal and vertical directions (

The higher the PPI value, the higher the density of the display screen. Of course, the higher the display density, the higher the fidelity. The standard for photos is approximately 300 PPI.

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

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

The relationship between the print size, the number of pixels of the image, and the print resolution can be expressed using the following calculation formula:

Number of horizontal (vertical) pixels of the image = print horizontal (vertical) resolution × horizontal (vertical) size of the print,

Number of horizontal (vertical) pixels of the image / printing horizontal (vertical) resolution = horizontal (vertical) size of the print.

For a particular image, the number of pixels in the image is fixed, so the print resolution and print size have an inverse relationship.

For example: If you want to print a photo with a size of 4 * 3inch, and the print resolution is 300dpi both horizontally and vertically, you need at least (300 * 4) * (300 * 3) = 1080000 pixels, about one megapixel. Too low the number of captured pixels will reduce the print quality of the image, and too high will not improve the print quality.

ppi Pixels per inch ppi

ppi (pixels per inch) is the unit of image resolution. The higher the ppi value of the image, the richer the details of the picture. Because there are more pixels per unit area, the pictures taken by the digital camera may vary depending on the brand or production time. Different, the common ones are 72ppi, 180ppi and 300ppi, which are so many by default (A710 shoots 180ppi, personally feel that this parameter seems to have little effect, generally no one mentions this). dpi (dots per inch) refers to output resolution. For output equipment, the output resolution of a general laser printer is 300dpi-600dpi, the typesetting machine for printing reaches 1200dpi-2400dpi, and the common printing is generally between 150dpi and 300dpi. between.

Pixel per inch contrast

ppi and dpi are indeed two concepts, but some things are agreed upon. The ppi of a picture cannot reflect the print quality that this picture can get in a print shop. You might as well go to the shop and try it. You ask the operator your The picture shows what kind of print quality 72ppi will get, and most operators will be confused. In the print shop, only dpi is used, because the pictures we take must be output as photos. For the operator, all he needs to know is your picture pixels and the size you need to print. These two elements constitute dpi. Therefore, although it is not standardized, we only use dpi to communicate the pictures that need to be printed.

"Getting to 300ppi in Photoshop has no practical significance and increases the volume of the image." Because this modification is a modification of the ppi under a fixed image size (size), which leads to the unreal expansion of the picture pixels. As a result, the volume of the picture is enlarged and the image quality is not improved (the extra pixels are calculated by interpolation). The correct way is to first crop your picture according to the proportion of the size you need to enlarge, and then fix the picture. Pixels (remove the check mark in front of "Redefine the pixels of the picture") and proportions, adjust the width and height in the "Document Size" to the same size as you want. The ppi at this time is your picture in this The dpi that can be obtained under the print size. If it is lower than 120, the printed effect will be worse. 120 ~ 200 indicates that the effect is okay. 300 is the best effect. If it is greater than 300, first "redefine the pixels of the picture". Check the box and change the ppi to 300 or lower.

(Note: 300dpi is the limit of the printer. Pictures larger than 300dpi will not improve the sharpness of the photo. In fact, 250 is enough. Even if you input an image file larger than 300dpi to the printer, the printer will calculate the picture first. 300dpi and then expand the printing. In addition, don't underestimate the 300dpi of the printer. The photo quality of the printer's 300dpi cannot be surpassed by any printing equipment.)