If you're looking for textbooks, the two big ones are "Real-Time Rendering"[1] and "Physically Based Rendering from Theory to Implementation"[2]. The former focuses on techniques used in real-time rendering (frames per second), while the later focuses on those used in offline rendering (seconds per frame). If you want something more bite-sized, you might try "Ray Tracing in One Weekend".
The first 3 chapters of "Real-Time Rendering" and all of "Ray Tracing in One Weekend" are freely available on the authors' website for free or pay what you want.
Physically Based Rendering looks great. I know that one of the authors - Matt Pharr - also has some great blog posts about "ispc", a compiler he wrote while at Intel: https://pharr.org/matt/blog/2018/04/30/ispc-all.html. If he was involved in a book in an area I was thinking about studying I would buy it in a heartbeat
The first 3 chapters of "Real-Time Rendering" and all of "Ray Tracing in One Weekend" are freely available on the authors' website for free or pay what you want.
[1]: http://www.realtimerendering.com/ [2]: https://www.pbrt.org/