Mavis 16.9.0 is available.
Amining to provide the best orthomosaics possible for your application, this release focuses on enhancements in orthomosaic generation. The methods implemented in Mavis comprise blending, locally adaptive exposure compensation and illumination correction.
While blending is aiming at joining two neighbouring images seamlessly, exposure compensation corrects changes in the colors due to changes in weather conditions and thus camera exposure settings, and illumination correction adjusts the combined effects of vignetting, BRDF illumination differences as well as 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.
To provide optimal results Mavis combines blending as well as local adaptive exposure compensation and illumination correction techniques. This results in sharp and high contrast orthomosaics.
All orthomosaics shown in the following are generated with different settings in Mavis to visualize the influence of the methods and their combinations. All data shown in the figures are raw image data (DN) without any pre- or post-processing (gamma adjustment, white balance, contrast enhancement, etc.) applied to the input images or the orthomosaics shown.
The first image is a raw orthomosaic without any algorithm applied. The seconds shows the effect of exposure compensation and the third of exposure compensation and illumination correction. In this third orthomosaic only a very few remaining seams between the single images remain visible. The fourth shows the result of blending without any other technique applied. The last image is generated using the default settings in Mavis with all approches integrated.
Fig. 1: Raw orthomosaic without blending, without exposure compensation, without illumination correction
Fig. 2: Orthomosaic without blending, with exposure compensation, without illumination correction
Fig. 3: Orthomosaic without blending, with exposure compensation, with illumination correction
Fig. 4: Orthomosaic with blending, without exposure compensation, without illumination correction
Fig. 5: Orthomosaic with blending, with exposure compensation, with illumination correction (Mavis default settings)
For illumination correction illumination errors are computed for each images. The following image shows three single orthoimages of the above example, their corrected versions as well as the corresponding illumination errors.
Fig. 6: Single ortho images, their corrected versions and the illumination error masks
The following two orthomosaics show the limitations of pure blending approaches. Both mosaics have been postprocessed in Mavis with the same enhancement settings (without contrast enhance). The first one shows the version solely based on blending, whereas the second one is based on the default settings in Mavis including illumination correction and exposure compensation. The blended version shows a much lower contrast.
Fig. 7: Orthomosaic using blending
Fig. 8: Orthomosaic based on the Mavis default settings
With changing weather conditions the differences are not only visible in contrast as in the above example but also in color. The next example shows the differences between a raw unblended orthomosaic and the final orthomosiac with blending, exposure compensation and illumination correction.
Fig. 9: Raw orthomosaic
Fig. 10: Orthomosaic with Mavis default settings