Although Bersoft Image Measurements (BIM) performs all measurements in pixels it can convert automatically the pixel values to any other measurements unit such as millimeters, microns, feet, miles, etc. The conversion is done by multiplying the pixel measurements values by a numeric constant called Conversion Factor.
The Conversion Factor can entered by hand or by drawing a line on the image and entering its real length.
To set the Conversion Factor use the Measurements -> Set Conversion Factor menu or click on the bottom of the Measurements Panel, where it displays the Conversion Factor.
To calculate the Conversion Factor by drawing a line that measures a known length object, follow these steps:
Draw a line with the tool.
Select the line either with the tool or by selecting the measurement in the Measurements Panel.
Click on the Measurements -> Set Conversion Factor menu.
Click on the Set from Line button. You can set either the Default Conversion factor or just the Conversion Factor for the current image*.
Some measurement tools make easy to normalize the way pictures are taken. Scanners, microscopes and other scientific measurement tools always take pictures from samples placed at the same distance. With knowing the DPI value or the microscope amplification factor, you can easily calculate the Conversion Factor, no matter if there is no known length object in the image.
Other tools, like digital cameras, produce images taken under far more variable conditions. The distance to the object may change from image to image, as well as the zoom or the camera lens. That makes more difficult calculating the Conversion Factor unless there is a known length object in the image that can be used to get the Conversion Factor.
Also, not all objects in an image from a camera may be placed at the same distance, so if the known length object is not placed near to the object the to measure you can lose accuracy. Learn More.
A simple method to calculate the conversion factor when working under changing conditions is to project a pair of laser beams parallel to the camera lens and fixed at a known distance between them. In that way two dots separated by a known distance will appear in all your pictures, providing a valid reference point to calculate the conversion factor.
By default, the Conversion Factor is set to 1. Therefore BIM will show measurements in pixels unless you define a different Conversion Factor.
The Status Bar on the bottom of the Measurements Panel shows both the Conversion Value for the current image (CV) and the Default Conversion Value (DCV), which is the value to be used as default when opening images that have no Conversion Value set.
* Each image can have a different conversion factor, but also there is a Default Conversion Factor, which will be the one used unless an specific conversion factor is set.