Smartphones have backlit screens, which makes it seem like certain images are bright enough. Most of your images will be printed without a significant difference, but it’s always best to improve the shadows or the brightness of an image that looks too dark or contrasty.
To do this, you can use your device's photo editor or use your favourite app. Our favourites are VSCO and Snapseed, as they are easy to use and free! However, any editor with Shadows/Highlights adjustments tools can be used. You can use “Brightness” or "Highlights" to increase the light of an image or “Shadows” to improve the dark areas only. "Contrast" also helps. " Exposure will affect the overall exposure.
The aim here is to have an image that it’s well balanced before printing to achieve a perfect result. Unless, of course, you like a dramatic look!