When the Surface mode is “Quality Textures” a number of advanced remappings and texture optimizations take place. The first is called perspective correction, and the second feathering.
Perspective distortion in textures is most noticeable with surfaces that are textured from photos taken at shallow angles to the surface. Only photos that are perfectly parallel to the surface have no perspective distortion. On some projects the distortion will not be very noticeable and on others the model will look poor without it.
Feathering is a process of blending the edges between different photographic source data. For example, if there are two surfaces that are side by side in the model but use different photographs as the source for photo-texturing (due to being forced to use those photos or because of angle settings etc.) the transition may be quite obvious. This is especially true if there are any color or intensity differences between the two photos. The feathering process smooths that transition so it is not as obvious.
Next to the Surfaces check-box in the 3D Viewer Options dialog is an "Update textures" button. Pressing Update will cause the textures to be recomputed (applies to fast and quality textures).
The algorithms used to form Quality textures are very advanced and exact and so it can be slow with big photographs. For this reason, PhotoModeler will display a user optional warning before recomputing the textures (e.g. after processing). When the textured model becomes in whole or in part untextured (white surfaces) you can enter the Options dialog and press the Update button to have the textures recomputed again.
There are settings in the Preferences dialog that control the processes that are carried out during quality texture creation. See Preferences - Exports and Output. For example, feathering for quality textures in the 3D Viewer may be turned off by default.