Digitising published graphs of component characteristics

Component manufacturers often publish in hardcopy or electronic form, graphs of component characteristics. This article presents a method of capturing that data for use in spreadsheets and other tools.

Step 1: Obtain / extract a digital image. If the source document is a hardcopy, scan it and crop out the graph of interest, if the source is electronic, extract and crop the graph image. A good format for the final image is PNG, do not at any stage create a JPG image as the compression algorithm creates artifacts that degrade the line art.
Step 2: Import the graphic into a suitable graph digitising package, I recommend Engauge digitiser and digitse the points. Be generous in taking samples in regions where the slope changes rapidly.

Above is an example of the characteristics of #52 ferrite material cropped from Fair-rite’s catalogue and digitised in engauge.

An excellent tool for capturing and cropping screen displays is Screenshot Captor, it was used to grab the above graphic from a displayed PDF file.

The next step in using the discrete samples is to use some form of interpolation such as discussed at Using my Excel cubic spline interpolation functions.

(The Engauge distribution lacks a Windows installer. For convenient installation, I have created a installable package of Engauge V4.1, you can download it here.)