Fast calibration#

Fast calibration is the usual choice for a screenshot, scan, or exported figure where the graph has not been photographed at a strong angle.

How to use it#

1. Choose Fast in Calibration.
2. Choose Calibrate all, then place X1, X2, Y1, and Y2 on known axis references.
3. Enter the graph value for each reference.
4. Choose Linear or Logarithmic independently for X and Y where appropriate.

The X and Y references can use unequal scales. Fast calibration also supports axes that are rotated or slightly sheared in the image, and axes may run in either direction.

Use Perspective calibration instead when a photograph makes the plot boundaries converge or appear noticeably warped.

Technical details#

GraphX uses the two calibrated image-axis directions as an affine coordinate basis. This maps image positions into graph coordinates without assuming that the graph axes are perfectly horizontal and vertical on screen.

For the complete affine and logarithmic transform explanation, see Calibration mathematics.