I am curious how High the bit depth of textures needs to be for High-Definition?
Was is the bit depth of standard definition and high definition anyway?
high definition (HD) video has many standard: 1280x720p, 1920x1080i to mention a few. But I don’t think it mentions bit depth. For the sake of of post, I’d say 24bit (8bit RGB) should be enough. For comparison, Elephants Dreamwas rendered and composed at 10bit per channel. The final output video is 8bit per channel.
Well, it gets more complicated - as mpan3 said Standard Definition and High definition only refer to frame size. The bit depth of the final output format will vary - for example if you’re rendering for film, it’s often 16bit or 10bit. It was 10 bit for the digital HDCam SR tape that we used to screen Elephants Dream in the theatre. For the web or normal video 8bit is fine.
But you’re talking about textures. For anything other than displacement maps or HDRI backrounds for image based lighting, you should be quite alright with just 8bit textures. You won’t see any additional dynamic range in bump, spec, etc maps and colour maps should ideally have very low dynamic range - you don’t want the lighting information already in the colour texture, you want to give that add that information (brightness) through your CG lighting setup.