Colocalization Colormap

Independent fluorescent  labelling of two different elements is a commonly used  method  to determine their colocalization in two superimposed microscopic images. The common algorithms utilised in this process are based on the comparison of general distributions of fluorescence intensities and do not provide any spatial representation of colocalization within the analyzed specimens. To overcome this limitation an advance to colocalization analysis has been proposed by Jaskolski et. al. (2005. The output image produced by this algorithm contains a pseudo-color map of correlations between pairs of corresponding pixels in two original input images, thereby offering quantitative visualization of colocalization. Hot colors int the map represent positive correlation (colocalization), whereas cold colors represent negative correlation (segregation).
Spatial representation of colocalization        
Correlation between individual pairs of pixels (normalized   mean deviation product -nMDP) is calculated according to the formula below.

Ai and Bi are the intensity values of particular ‘i’ pixel in the images A and B.

A ̅ and B ̅ are means, Amax and Bmax are maxima in the given images.

Distribution of nMDP values (ranging from -1 to 1) is visualized with a color scale. Negative indexes are represented by  cold colors (exclusion). Indexes above 0 are represented by hot colors (coocalization).

Automatic colocalization calculation visualization Colocalization Colormap plugin.
(A) Mouse brain section. Neuronal body and dendritic processes stained with antibody against MAP2 protein.
(B) Immunoreactivity of CD44 adhesion molecule in the same brain section.
(C-D) Colormap representing colocalization between adhesion molecule and MAP2 neuronal marker.