DVI is an 8 bit RGB signal, while HDMI can be 8 bit RGB, or 8 bit, 10 bit, or 12 bit YCbCr. If you have a DVI source and DVI display, there will be no problem. If you have a DVI source and an HDMI display, again, no problem. If however, you have an HDMI source and a DVI display, the below-black video information may be lost in the translation. There is a bug in the Silicon Image HDMI transmitter that pops up when converting YCbCr to RGB. The HD TiVo and Pioneer 59AVi do not have this problem.
Even though source information (DVDs, HD) is all 8 bit color, if DSP is applied in 8 bit, such as in a video processor, rounding errors will toss out some of the data. On the other hand, if the data are 10 bit, such as with YCbCr, then the rounding errors don't occur. In fact, 14 - 16 bit is optimum for processing. Also, DVD data are YCbCr, and are converted to RGB in the player for the DVI output. RGB cannot represent all the data in YCbCr, and this is why the below-black information gets truncated.