DVI - video levels and color space

[HD Library]

DVI originated from the computer world. There are two standards for DVI digital video streams.

RGB 4:4:4 sampling rate
YCbCr 4:4:4 sampling rate

While both are supported in the DVI specifications in practice DVI YCbCr is rarely used and most sources and displays are setup for RGB encoding

DVI-PC RGB is for your computer and uses a range of 0-255.

DVI-video RGB is for your home theater and uses a range of 16-235.

DVI-video is for your home theater system which is YCbCr and uses a uses a video, Y, range of 16-235 and a color, Cb and Cr, range of 16-240. It also can use the color space of SD or HD depending on the selected SD or HD scan rate.

While both are available in practice DVI source and display connection typically use RGB encoding. These levels must be set correctly by the manufacturer for the intended application of the product whether source or display. If not you will have problems such as crushed blacks or crushed peak whites or the opposite of low peak light output and washed out blacks. While you may be able to compensate for these errors using the brightness and contrast controls of the display, in practice there will be a penalty in imaging by doing so.

Another point with video content is which color space the source is using to convert YCbCr signals to RGB for delivery to the display. If the source, such as a DVD player, is not setup to output the ITU Rec. 601 standard for SD sources regardless of the selected output scan rate you will have a color decoder error. In this case outputting the HD ITU Rec. 709 color space when selecting 720P or 1080I output would be an error on the part of the source since color decoding is a process that occurs prior to any RGB delivery. The same error would occur with a satellite or cable receiver that is converting SD channels to HD color space because you have selected 720P or 1080I conversion of these signals. For a display to compensate for this error would require it convert the incoming RGB to YcbCr, make the necessary color space correction and convert it back to RGB for the final stage of driving the imaging technology. Based on specifications the display has no reason to provide this capability.

Improper color space selection results in improper color saturation and tint. Will you notice? Hard to say as the perception will be viewer dependent without a reference point but if you are making comparisons of products this is critical to your evaluation.

If your source is HDMI and you are using an adaptor for DVI there is another set of pitfalls to be aware of.

HDMI - video levels and color space