The resolution is how many pixels per inch (PPI) there are in a photo, and this value determines your image's sharpness. While it's common for images shown on the web to have a lower 72 PPI resolution, the University of Michigan recommends a higher resolution of at least 200 to 300 PPI for images you want to print in good quality. Whether you need to increase the resolution of the image or reduce it, you can find tools for Windows and Mac that can do the job easily.
Basics of Changing Image Resolution
Raising the resolution of an image increases how many pixels it has vertically and horizontally, while reducing the resolution decreases the number of pixels. When you change a picture's resolution, this does not also change the actual dimensions or the file size. However, it does affect how large the image is physically printed on paper since you're increasing or decreasing the pixels per inch. For example, changing a 300 PPI image to 600 PPI would reduce the printed image size to half.
Popular image editing tools often by default select an additional option to resample your image when you make any changes to its size or resolution. When you use this option, the program will adjust how many pixels there are in the image to align with the new resolution. This can cause your image quality to degrade, so you may prefer to avoid resampling.
Change Image Resolution With Photoshop
If you subscribe to Adobe Creative Cloud and have Photoshop CC installed, you can open the photo in the program and then select "Image Size" from the "Image" menu to access the image sizing information. Type the resolution you want beside "Resolution" and ensure "Pixels/Inch" is selected in the unit drop-down menu. If you don't want to resample your image, uncheck the "Resample" box. You can then click "OK" to set the new image resolution.
Change Image Resolution With Preview
Mac OS users can change the resolution of image files using the built-in Preview app used to view, convert and edit images and PDF documents. After opening your image in Preview, select the "Tools" menu and choose "Adjust Size" to see the image's current size and resolution. Use the "Resolution" box to specify the resolution you want. If you don't want the number of pixels to go up or down with the resolution, uncheck "Resample Image." Click "OK" to change the resolution.
Change Image Resolution With GIMP
Whether you run Windows, Linux or Mac OS, you can download and use the free image editing tool GIMP to change the resolution of image files. Open your image in GIMP and then select "Scale Image" from the "Image" menu. Set the desired resolution value in both the "X resolution" and "Y resolution" boxes. If you don't want resampling enabled, select "None" for the "Interpolation" setting. Click "Scale" to apply the new image settings.