The Gradient Brightness Correction is required when you observe a slow brightening or darkening when sliding through the image in one direction.

First choose the Direction along which the gradient occurs: X, Y, or Z.

The Correction Method provides the two options Multiplicative and Additive. The choice of method depends on the processing applied by the image acquisition device. The scanned image data usually provides information about whether the acquisition device uses linear or logarithmic image processing. If the processing is linear, use the Multiplicative correction method. If the processing is logarithmic, use the Additive correction method.

With Enabled ROI the gray value range can be restricted within which the correction is applied. The according minimum and maximum gray value of that range are chosen in the Histogram ROI.

Click Apply to correct the Gradient Brightness according to the given settings.

The following example shows a brightness gradient from exterior to interior in a Z-axis slice. That gradient can also be observed in the Slice Mean gray value (see the Histogram section), shown in the following diagrams for the X-axis. The Gradient Brightness Correction is applied for Direction X without Enabled ROI. The correction improves the gray value image significantly. As a result, the gray value histogram now shows a strongly improved differentiation between pore space and solid phases. The slice mean gray values now have a linear trend along the X-axis.