Resolution Test Image

June 6, 2024

This page describes a basic resolving power test for verifying the angular resolution of a smartphone camera with or without a binocular/monocular attachment. A test image was created manually using the Win11 basic Paint application. The synthesized image size is 1440x2960 pixels, the display size of the Samsung S9 smartphone which I used as the image display device. The photo at right shows the S9 full screen test pattern photographed at close range with an S23 Ultra phone. The resolution test involves viewing/photographing this test pattern at a distance L = 30' (9144 mm) and checking which dots can be clearly resolved as separate features. The S9 display has a pixel density of 568ppi or 22.4 pixels-per-mm or 0.045 mm/pixel. For example, the two dots at the bottom of the test pattern are separated by 60 pixels, so the physical separation on the display is W = 2.7mm as verified by careful measurement of the S9 display. At the 30' measurement distance, the angular separation in radians of these 2 widest dots is:
θ = W/L = 2.7/9144 rad
   or in arc-seconds:
θ = 180/π*3600*(W/L) ~ 60∠"
which is about the angular resolution of a typical good human eye.
So at this 30' distance between test image on the S9 and camera (device to be tested), the angular width scale is conveniently ~ 1∠" per pixel. (For other display devices, see examples at bottom of page)

All "dots" in the test image are solid "white". A macro photo at right shows the actual RGB pixel details for the upper 20 pixel circle of the test pattern on the S9 phone display. The pattern from top to bottom is:
  A large 20 pixel diam circle   20 ∠" width
The remaining 6 rows each contain two 3x3 pixel squares with increasing separation:
  10 pixels   10 ∠"
  20 pixels   20 ∠"
  30 pixels   30 ∠"
  40 pixels   40 ∠"
  50 pixels   50 ∠"
  60 pixels   60 ∠"

Examples

The photos below were taken with the S23 Ultra alone (LEFT) and with the S23 Ultra + Gosky 12x55mm monocular (RIGHT) at a 30' distance from the test pattern on an S9 phone as discussed above. The image at left shows that the 30 ∠" spots are barely resolved. The is in reasonable agreement with the resolution expected for a 5mm camera lens using the X10 camera.
The image at right with the Gosky monocular shows resolution down to the closest spots of 10∠" clearly demonstrating the resolution improvement using a reasonably good larger lens in front of the S23 Ultra camera for increased resolution. For perfect lenses (both the smartphone 5mm and the 55mm monocular), the theoretical best resolution would be ~ 3 ∠").



For other display devices, in full screen mode, the horizontal distance measured for the widest "60 pixels" dots are: