Dots per inch (DPI) refers to how many ink dots there are for each inch of an image printed on a piece of paper. When you want to have something printed professionally or need a high-quality print at home, 300 DPI is the standard for print resolution because it accommodates high detail in graphics. While you won't find an option specifically to change the DPI resolution in Photoshop, you can update an image's pixels per inch (PPI) to 300, which causes Photoshop to update the print resolution accordingly. However, it's important to note that making this change does not make a low-quality image look better.
How DPI and PPI Relate
It's common for the terms DPI and PPI to be confused and used interchangeably because both are related to resolution and clarity, but they differ in a focus on print versus digital image quality. The DPI refers to how sharp an image can print in terms of the number of physical printed dots. PPI refers to an actual image's resolution in terms of how many pixels there are for each inch on your computer's screen.
For example, printing a 300 DPI image means there are 300 dots for each inch on the paper. An image displayed at 100 percent size with a 300 PPI has 300 pixels for each inch on your screen.
Change DPI in Photoshop
To set the resolution at which your image prints, you can change your image's PPI through Photoshop's image sizing options. After you open the image in Photoshop, select the "Image" menu and choose "Image Size" to access those settings. Type "300" in the box for "Resolution," which is the term Photoshop uses for the PPI, and make sure that "Pixels/Inch" is set on the unit drop-down menu.
Below the image size options, you'll see a checkbox and menu named "Resample" that is checked by default. This option makes Photoshop update your image's actual height and width dimensions to align with the new 300 PPI resolution, and this increase in image size can make low-quality images look worse and pixelated. Therefore, if you want your image's actual dimensions to remain the same and the quality to be unaffected, uncheck the "Resample" option. Finally, click "OK" to update the image settings and then save the image.
Effects of Changing Print Resolution
After you set an image's PPI to 300, your image will use 300 pixels per each inch on your screen. You will also be able to see the updated 300 PPI value listed as the "print resolution" in the print preview within Photoshop. However, changing the image's resolution does not make an originally low-quality image display or print in high quality because you're limited by the image's original quality. Therefore, it's recommended to start with a high-quality image in the first place if you need to print it in good quality, whether you are creating a graphic on your own or seeking photos from another source.