DVD's on a PC - 16bit color vs. 24bit (1 Viewer)

[MarkHastings]

I work with someone who was trying to play a DVD on her computer. The computer is pretty old and wouldn't play the DVD with the monitor set to 1024x768 / 24 bit color. She didn't want the screen res. smaller, so I lowered the color to 16 bit and the DVD played. The DVD we were looking at was a DVD-R that someone burned and the quality was pretty bad, but she asked me if she viewed it on a better system, would the video look better.

So my question is, does it make a big difference (if any) between watching DVD's in 16 bit as opposed to 24 bit? Isn't the NTSC palette limited enough that 24 bit won't give you any more colors?

 

[Matt DeVillier]

Mark,

DVD, like other video on a PC, is played back using an overlay surface (prior to DX9 anyway, which we can safely assume based on the age of the computer is not installed). The color depth and format of the overlay surface are fixed by the program which created it. In the case of DVDs, the overlay is fixed to 24-bit color.

The reason the computer wouldn't play the dvd with the desktop color set to 24-bit is it probably lacked the video memory to have both the desktop and overlay surface resident in memory at the same time. A 1024x768 desktop at 24-bit requires 2.25MB of video memory, and an 640 x 480 overlay (assume non-anamorphic, square pixels) at 24-bit requires an additional .88MB (1.165MB for anamorphic). Since video playback is usually double-buffered, that jumps to 1.76MB (2.33 for anamorphic). If the computer you were using only has 4MB of video memory, then that would explain why it wasn't able to play back the DVD when running 24-bit desktop (2.25 + 1.76 > 4). A 16-bit desktop takes only 1.5MB, leaving plenty of room for the overlay.

the short answer is the dvd is being played back at 24-bit, and adjusting the desktop resolution won't change the quality of DVD video playback

 

[MarkHastings]

In the case of DVDs, the overlay is fixed to 24-bit color.

I knew about the 'overlay' thing, but I didn't realize it was independent of the desktop color setting.

Thanks