If you are a long time hacker, you might remember all resistor color codes so well that you have no problem in reading them without thinking to much. For other there are those resistor color code tables and calculators.
But could this task be automated? Maybe with mobile phone? Reading Resistors With OpenCV posting mentions a new open source Android app to do that: Resistor Scanner. This app uses OpenCV Open Source Computer Vision Library to scan resistor colour bands and determines resistor values (source available at https://github.com/thegouger/ResistorScanner/). Take a look at the operation of this app with this video:
The app looks really interesting. So I had to try it. I installed it to my Android smart phone, but I has disappointed with the performance. The reading of the resistors did not seem to be very reliable and it did not read many resistors at all. The problems seem to be centered with the fact that I could not get goo big enough picture of the resistor on the smart phone screen (not enough zoom and smart phone does not focus well to very near objects). The app worked with some larger power resistors, but not with normal 1/4W resistors. Maybe I have to make second test with some smart phone macro lens or something some day. It also seemed to have some issues on detecting the correct colors. According to Hackaday discussion this app has things to improve “it is a naive implementation that will read the codes in the ideal conditions “.
If you can’t use this this Android app, because you have Apple device, then Hackaday tips that there is iOS app called called ResistorVision (plans to release an Android version of ResistorVision in the near future).