There has been a divergence between the rendering algorithms
and illumination models used for interactive use and
those used for high quality realistic image generation. For
users this has often required them to switch between two
different rendering modes. Lower quality renderers are used
for interactive tasks such as modelling, viewpoint selection,
and walkthroughs. Computationally expensive illumination
effects such as shadows, reflections, refraction, and global
illumination are provided at low fidelity or omitted entirely.
To see their work under the full illumination model, the user
must switch to a higher quality non-interactive renderer that
often takes minutes or longer to produce a single image.
Such mode switches disrupt the user’s concentration, and
can make fine-tuning their work a very tedious process.