I've been using Datathief III for a few years. It is a shareware java app that can extract data from an image. It works best on line graphs, but you can use it on any type of data with two axes (that excludes pie charts). All you need is define three reference points on the axes
(0,500) in your first image, then you are ready to go.
It has two modes, trace and points. Trace automatically captures data by following the color of the selected line, whereas points allows you to place points manually.
Using trace mode requires defining the start and end points of the data, as well as the line color. Here is an example:
Using points mode is better when you have a specific set of points:
The output here is:
Better accuracy can be achieved with further fine tuning.
- Fast and accurate
- Traces data automatically, and allows for manual adjustments
- Does not support pie graphs
- Shareware - not open source