Tracer is a utility for digitising data from images of graphs (which could be scanned or perhaps extracted from PDF files). The image is scaled according to the plot axes, and data are created in an attempt to follow a trace across the image between endpoints marked by cursors. The data are extracted at the resolution of the image (one data point per pixel). In the event that the curve does not form a continuous path between the cursors (due to poor image resolution or use of dashed lines), the procedure attempts to search for the next line segment. I've tried to build in some colour recognition features.

If you want to digitise data as individual points picked from a graph image, check out the Wavemetrics procedure IgorThief, available from the FTP archive.

How to use Tracer:

• Select Start Tracer from macros menu.
• Load and display an image using the buttons on the Tracer panel.
• Check boxes for log axes
• Place cursors on a pair of known x or y values, type those values
  into the relevant boxes in the Set Scale area of the Tracer panel,
  then click on 'Set X' or 'Set Y' to set the image scaling. Make
  sure the cursor positions are accurately reported in the panel before
  moving on.
• Select trace and background colours in the colour selector area
  of the Tracer panel. To sample colours from the image, click the
  'csr' button and move the cursor over the image. When the popup
  menu shows the colour you want to select, click with the mouse to
  set the colour.
• The 'fuzziness' slider affects how picky the tracer is about colours.
• Select a name for the wave that will be created with the extracted
  data.
• Place cursors at start and end of a trace and click on 'Trace'
  to start digitising.
• Play with the gaps and jump threshold settings to deal with incomplete
  lines and other problems.
• If needed, you could use interpolate to clean up your traced data.

Releases