Immix aligns and merges a set of similar images in order to decrease their noise.
In a low-light environment, when the flash is not an option (for distance or lighting quality reasons), a digital photographer has the option of either using a low-ISO (low sensibility) setting with a long exposure time, or using a high-ISO setting with a shorter exposure time.
While the former produces high-quality output, the long exposure time involved imposes the use of a tripod (otherwise the image will be blurred).
On the other hand, a high sensibility allows handy exposure times, but at the expense of increased numerical noise - this approach is in fact automatically chosen by most cameras.
The third option consists of taking several pictures of the same scene with a short exposure, then aligning them and merging them to decrease the noise. The signal/noise ratio grows with the square root of the number of images : for example, a combination of 16 ISO 400 images has no more noise than a single ISO 100 image.