Research note: Exposure Artifacts and Shadows

One of the next updates of Mavis will include options to automatically adjust the image color according to changes in solar irradiance as well as the option to automatically remove shadows


Exposure


Generating orthomosaics involves blending neighboring images to avoid artifacts at the boundaries between two images. If the exposure settings of the camera are stable over the entire flight, no further processing is usually required.

However, if there are changes in solar irradiance there might be changes in the camera settings resulting in color and luminance differences between neighboring images. Such differences can only be removed to a certain degree by blending as well as by common techniques to compensate exposure of neighboring images.

The following image shows an example of a flight with changes in solar radiation. The upper left image shows the orthomosiac without blending and without exposure correction. The differences in color and luminance are obvious. The upper right image shows the changes in solar irradiance – the lighter the color the higher the irradiance. The bottom row shows the blended orthomosaic without (left side) and with exposure correction (right side) as will be implemented in Mavis.

Example_ExposureCorrection_3

 


Shadows


Another related problem is cloud shadows. Even though there is little influence of shadows when calculating vegetation indices, visual interpretation of the data (especially for RGB imagery) can be problematic if shadows are present.

The image below shows the effect of shadow removal on a single image (top) and the resulting orthomosaic (bottom).

Example_Shadow_3

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