Concrete bubble

Concrete bubble quantification for classification


Responsible person: Godefroid Dislaire

Supervisor: Pr. Luc Courard

Collaborations:  CSTC WTCB


Exposed concrete must meet several requirements. Requirements are already made technological point of view, structural or functional and designers refer to various Belgian and European standards.

The WTCB -CSTC (1) is normalizing aesthetic requirements of exposed concrete. These requirements relate to the texture, the number and size of the bubbles and the homogeneity of the color. This standard is an extension of the standard EN 206-1 , NBN B 15-001 and DIN EN 13670 .

The next image processing intends to measure the surface proportion of bubbles less than 2 mm, bubbles of 2 to 15 mm and bubbles over 15 mm ( defects) . According to thesurface percentage of bubbles of 2 to 15 mm, it will be standard , high quality or high quality.

Click on the image to see the animated gif

The threshold used the Otsu algorithm optimized to cut bimodal (black and white) distribution of pixels.

Nevertheless to give good result the image has to be cleaned of non-uniform lighting and non-uniform concrete texture and color.

This is done by removing the background from the image. This background is provided by a morphological closing and better by a morphological erosion followed by a reconstruction (2).



Morphological closing




Morphological erosion followed by a reconstruction.




Background corrected image


(1) The WTCB CSTC is a research institute funded primarily by 90000 Belgian companies representing all construction trades , which leads scientific and technical research for the benefit of its members, providing technical advice and contributing to innovation in order to improve the competitiveness of these.


(2) Morphological Grayscale Reconstruction in Image Analysis: Applications and Ecient Algorithms, Luc Vincent.