You can import an image that contains log axes into Grapher. The method described in the knowledge base article, "Import an image and extract data from it in Grapher" will not work because Grapher only allows linear coordinates to be defined for calibrating the image. However a slight work-around can be used.

 

Follow these steps if the image has log, ln, or other Grapher recognized axis scales:

1. Click the File | Import command.
2. Select the image and click Open.
3. Click the Home | New Graph | Basic | Y=f(X) Function Plot () command.
4. Click on the X Axis to select it.
5. In the Property Manager, click on the Axis tab.
6. Set the Scale to the appropriate axis scale for the image. If the X axis in the image is Log, select Log (base 10).
7. In the Limits section, set the Minimum and Maximum values to values that are in the image.
8. Carefully move the X Axis so the minimum value (left side of the axis) aligns with the same value in the image. This may require zooming in and multiple moves of the axis.
9. Click on the far right handle of the axis. Hold down the left mouse button and drag the axis smaller or larger until the maximum value (right side of the axis) aligns with the same value in the image. Again, this may require zooming and multiple resizes of the axis.
10. Repeat steps 5-9 for the Y Axis.
11. Click on the Function Plot to select it.
12. In the Property Manager, click on the Plot tab.
13. In the Y = F(X) = box, type X for the equation. This will create a straight line. It is also recommended that you reset the First value and Last value to the X axis minimum and maximum values.
14. When the axes are aligned with the image, click on the Function Plot to select it.
15. Click the Insert | Image Editing | Digitize command.
16. Click on the image where you want a data point. A report window appears with the X and Y coordinates of the point you clicked.
17. Repeat step 16 until all data points are displayed in the report window.
18. Press the ESC key on the keyboard to end digitizing mode.

 

The report window can be saved as a data file. Alternatively, the data can be copied and pasted into a worksheet window. This data file can be used to create a new graph. The function plot graph can be deleted once the data is collected.

 

Updated July 22, 2019