I want to show an image as a fullscreen ad. What should be the image's size and pixel density, so that the same image can be used for Android and iOS phones/tablets.
I did some research and Google Admob's doc shows that they follow two different sizes - 480x320 for phone and 768x1024 for tablets.
Although I trust Google, but please let me know about other details like DPI of the image.
Thanks!
You can't use one image for all smartphones and tablets.
Apple uses @1x, @2x and @3x for different screen sizes and resolutions (phone/tablet and pre-retina/retina).
iOS uses a coordinate system to place content onscreen. This coordinate system is based on measurements in points, which map to pixels in the display. On a standard-resolution screen, one point (1/72 of an inch) is equal to one pixel. High-resolution screens have a higher pixel density. Because there are more pixels in the same amount of physical space, there are more pixels per point. As a result, high-resolution displays require images with more pixels.
Source: Human Interface Guidelines: Image Size and Resolution
Material Design (Android) talks about density-independent pixels (dp).
A dp is equal to one physical pixel on a screen with a density of 160. To calculate dp:
dp = (width in pixels * 160) / screen density
Source: Units & measurements
To help you out there are many online tools and tutorials. You can also setup documents and templates in Photoshop and Sketch.
