Fri, 08/31/2007 - 01:46 pm
Tracer is a utility for digitizing data from images of graphs (which could be screenshots or scans). The interface includes tools for setting the image scale so that coordinates match those of the graph in the image. Data are created in an attempt to follow a trace from left to right across the image between endpoints marked by cursors. The data are extracted at the resolution of the image (one data point per pixel). When the trace does not form a continuous path between the cursors (owing to poor image resolution, crossing lines, or dashed or dotted line types), the procedure attempts to search for the next line segment. Tracer distinguishes between different trace colors.
If you want to digitize data as individual points picked from a graph image, check out the Wavemetrics procedure IgorThief. Look under File > Example experiments > Techniques > Trace Graph.
Note that (unlike Trace Graph) Tracer doesn't make any correction for image skew, i.e. the axes are assumed to run parallel to the edges of the image.
How to use Tracer:
- Select Tracer from the Macros menu.
- Load and display an image using the buttons in the Image Selection area of the Tracer panel.
- Set Scale: Click 'Show' to add two pairs of horizontal and vertical cursors to the plot. Drag the cursors to known positions at the ends of the plot axes, then type the axis values in the SetVariable controls. Make sure the cursor positions are accurately reported before moving on.
- Select trace color in the color selector area of the Tracer panel. To sample colors from the image, look for the eye dropper icon in the color-picker dialog.
- The 'fuzziness' slider affects how picky the tracer is about colors. You may have to adjust this setting for tracing to work.
- Extract: Select a name for the wave that will be created with the extracted data.
- Place cursors A and B at start and end of a trace and click on 'Extract Trace' to start digitizing.
- Play with the gaps, jump threshold, and minimum range settings to deal with incomplete lines and other problems.
- If you're tracing a series of open symbols, use the minimum range setting to avoid tracing the symbol stroke.
- If needed, you could use interpolate to clean up your traced data.
If you want to help Tracer to take the right path where traces cross one another, you can use the image editing button to touch up the image. Hold down the control key and click with the mouse to paint pixels with the trace color, or the option/alt key to paint with the background color. Expand the graph view for more detailed editing. Use command/ctrl and scroll to zoom in and out, hold the shift key to accelerate zoom.
If tracing fails, be sure to try changing the fuzziness, jump threshold and gaps settings.
Current Project Release
|Version Date:||Sun, 07/04/2021 - 05:59 am|
|Version Patch Level:||5|
|OS Compatibility:||Windows Mac-Intel|
Minor adjustments to code for setting image scale.
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