I had a question about the accuracy of the line draw tool. I am conducting an experiment which I measure the displacement of microscopic particles, so I will use the Image/J software to measure the trajectory of each particle. In order to get the distance in millimeters, I must apply a scale, pixels/mm. I can do this by drawing a line on an imagine of a ruler I capture and then using the settings to apply a scale. I want to know what the uncertainty in the pixel measurement is, in other words how accurate is the line in counting pixels and what is the margin of error?
Welcome to the forum.
Line selections and measurements can be done with subpixel accuracy.
The exact length of the line is shown in the status line.
Note: If you press the SHIFT key during selecting the line the line will be drawn only in the direction 0°, 45° or 90°. This can ease the calibration.