Blooming - Bright Spots in the Point Cloud
Blooming is an effect that occurs when extremely intense light from a point or region hits the imaging sensor and results in over-saturation. In this article we discuss what blooming is and what causes it.
When the intensity of light gets too high the pixel gets “blinded”. The light from the pixel will spill into its neighbors with an intensity and radius that is proportional to the intensity of the incident light. This effect typically happens when a camera is pointed either directly, or indirectly by reflection, at a strong light source such as the sun or a strong lamp. Blooming can occur in the entire image or only in parts of an image. In the image below, the sun is reflecting in the ocean which causes a larger region of the image to become completely white. Distinguishing details within the affected regions becomes very difficult.
In this other image of a dandelion below, the starch of the dandelion appears to be bright orange in the region that is in front of the sun. The actual origin of this orange light comes from the pixels on the sides of the starch that are looking directly at the sun. The light from the sun is so intense that the light in those pixels spills into their darker, neighboring pixels that are seen in the starch.
Specular or reflective surfaces in the image scene which align such that the projector light is reflected straight back into the camera can cause blooming. Depth from over-saturated pixels cannot be accurately calculated and will, therefore, be filtered out. It is recommended to try to avoid these effects if possible. A typical scenario is when the camera is positioned to look straight down at a plane, such as a table. In this case, the projector may blind the camera and over-saturate it. The effect will appear as a completely white spot in the image, which translates to a “hole” in the point cloud with no points. This can be seen in the image below.
To learn about how to deal with blooming artifacts, please see How to deal with Blooming