Bluray can provide the illusion of 10-bit color depth?

[audiohominis]

Hi, guys.

Michael Cioni, in his Creatasphere Bit Depth video (http://www.youtube.com/watch?v=IujXVlz-y54#t=104) goes on to say this:By taking the information from a 10bit source and putting it on Bluray you get the perception that Bluray is giving you a 10bit display when it is actually only producing 8bit.
Can someone kindly elaborate on this, please. I'm not questioning the guy's authority in anyway, but how is that even possible? How does that work? :confused:

Thanks

[TheSkiller]

It's because if you produce a video in higher bitdepth you do all the calculations much more precisely than if you do it in 8 bit, and then, in the end, you may dither it down (i.e. you reduce it intelligently) to 8 bits and you get virtually perfect 8 bit video without any banding. In other words, you get the illusion of a higher bitdeph. Sure, it's not really 10 bits but it does look almost like it (imo).

Edit: So, even good ol' DVD can provide that illusion, not just Blu-ray.

[audiohominis]

Oh, I see. In a way it's not unlike mimicking smoother gradients via dithering when working with indexed color images, ha?
So this includes not just Blurays and DVDs but H264 and MPEG2 in general?

[Asmodian]

You need very high bit depths to preserve dithering so I do not think much would survive DVD compression but blurays do use rather high bit rates.

[kolak]

All "properly" done BD titles use high quality dithering.
Masters are delivered mainly as HDCAM-SR tapes, ProRes, 10bit YUV or DPX (TIFF) files, so all have 10bit precision. As a part of encoding process authoring houses convert 10bit sources into 8bit and than perform encoding. This can be a separate process, but in most cases current BD encoders have built in dithering filters. Some studios sometimes deliver special masters for BD.

If you don't use dithering (specially on CGI titles) than this can end up with very visible banding artefacts.

[foxyshadis]

DVDs can use up to 10-bit DC, which does make a difference with banding (compare the sky on a proper low-bitrate DVD with any xvid or early x264), though not as much as a full 10-bit transform. In a way, Blu-ray is a step back in potential quality, although the insane amount of bitrate available for dithering and grain makes up for it. It's people trying to create polished BD9s and BD5s who get the short end.

[kolak]

You need very high bit depths to preserve dithering so I do not think much would survive DVD compression but blurays do use rather high bit rates.

Dithering helps for DVD also, not as much as in case of BD, but difference can be clearly visible.

[TheSkiller]

How well the dithering survives the encoding not just depends on the compression/bitrate/encoder but also on the dither algorithm used. The more "randomized" ones (error diffusion) are less resilient to lossy compression than the more "ordered" ones.