What Is Pixel Density?

Pixels Per Inch is also called pixel density, which means the number of pixels per inch. Therefore, the higher the PPI value, it means that the display can display images at a higher density. Of course, the higher the display density, the higher the fidelity

PPI

(Number of pixels)

PPI concept

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 PPI ppi

ppi (pixels per inch) is a unit of image resolution. The higher the ppi value of an image, the richer the details of the picture. Because there are more pixels per unit area, the pictures taken by digital cameras may vary depending on the brand or production time. The difference is that there are 72ppi, 180ppi, and 300ppi in common, so there are so many by default (A710 shoots 180ppi, personally I feel that this parameter seems to have little effect, and 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.

PPI comparison

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 the difference). 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 checkmark in front of "Redefine the pixels of the picture") and proportions, adjust the width and height in "Document Size" to the same size as you want. The ppi at this time is your picture. The dpi that can be obtained under this print size. If it is lower than 120, the printed effect will be poor. 120 ~ 200 indicates that the effect is OK. 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 before printing)