This is selected with Constant . The opacity used is set with the alfa slider and the actual value is . This menu allows to choose two simple transformations of the values in the cube. The default is that xray and krot make an image that has the same pixel size as the data. If these images are small compared to the display window, it will expand these images using pixel replication.
Blocky images are the result.
Note that using an Expand factor of eg. One problem with volume rendering is that in order to see faint structures in the data cube, one has to set the opacities, intensity transformation and clips such that also the noise becomes bright. As a consequence, the emission is visible only through a thick fog of noise and this noise hides a lot of information. There are several techniques to do this. At the moment two algorithms are implemented, but we are working on other filters.