Resolution and a Picture’s Appearance and Quality
Before you print a digital photo, you specify an output resolution, which determines the number of pixels per inch (ppi) in the printed picture. Output resolution, also called image resolution or simply resolution, helps determine the quality of your printed digital photos.
The more pixels per inch, the crisper the picture. These figures show the same image at different output resolutions.
Why does the 75-ppi image look so much worse than its higher-resolution counterparts? Because at 75 ppi, the pixels are bigger. After all, if you divide an inch into 75 squares, the squares are significantly larger than if you divide the inch into 150 squares or 300 squares.