Mavis provides two options to generate orthomosaics - based on statistical exposure compensation or multi band image blending.
The statistical approach as well as blending comprise initial exposure and illumination compensation. These correct changes in colors and illumination due to changes in weather conditions and thus camera exposure settings as well as combined effects of vignetting, BRDF illumination differences and over- and underexposure effects resulting from changes in brightness across the image.
The influence of exposure differences is most visible in image sets where strong changes in weather conditions occur during flight. These can result in changes in aperture, shutter-speed and ISO settings and thus color and brightness gradients across the orthomosaic.
While the statistical approach uses additional compensation techniques blending uses multi band blending. Blending is faster but might result in over-compensation and contrast reduction
The following figure gives examples of the first step of illumination correction of single orthoimages.
- Weight assigned to the colors of the single ortho images in case of uncertainties in dense matching. A lower weigth puts increases the effect of exposure compensation.
- The higher the strength the stronger the blending effect.
- Compensation can be switched off for blending
- The image background can be either transparent or black. A transparent background results in larger image files.
- Factor of the maximum image size in relation to the input image size. If a single ortho image exceeds this size the image is not used for generating the orthomosaic, because it is taken not vertical and to provide a "true" orthomosaic.