The red marks are uncalibrated cameras.
It means that the algorithm has not been able to find enough tie points between the different images which lead to a high number of uncalibrated images.
I recommend you this article to understand better the cause of this: [Quality Report Help
](https://support.pix4d.com/hc/en-us/articles/202558689-Quality-Report-Help#label101)In your case, it seems that it is due to the nature of the terrain and especially the area with dense vegetation.
Trees and dense vegetation often have a very different appearance between overlapping images due to their complex geometry (thousands of branches and leaves).
Therefore, the overlap may need to be increased (> 80%). Flying at high altitudes often reduces visual complexity and improves outcomes, especially in forests and dense vegetation environments. At higher altitudes, there is less perspective distortion (resulting in fewer appearance problems) and the dense vegetation has better visual characteristics. In other words, it is easier to see visual similarities between overlapping images in such areas.
Step 1. Before Starting a Project > 1. Designing the Image Acquisition Plan > a. Selecting the Image Acquisition Plan Type
How to improve the outputs of dense vegetation areas?
At this point I can recommend you to work with a lower image scale as it usually gives better results than the full scale for such images.
[1. Initial Processing > General
](https://support.pix4d.com/hc/en-us/articles/202557759#label3)Using “All Prior” for the Camera Optimization could also lead to a higher number of calibrated images
If it does not improve the calibration yet, fly again at a higher altitude with a 90% overlap.
Hope this will help you to improve the quality of your project,