Re: JPS?

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Thu, 24 Apr 1997
>From: P3D John W Roberts asks:
>
>
>One thing seemed a little ambiguous in yesterday's discussion of JPS:
>why do you need *shutter glasses* to view a side-by-side stereo image?
>Shutter glasses are normally used for sequential field or sequential frame
>stereo. It would seem to make sense if the video card takes the "side by
>side" images from the JPS data and displays them sequentially. But several
>people made a point of emphasizing that the display is not *interlaced*
>(field sequential). Does that mean the display is *frame sequential*,
>or something totally different? 

*****  You don't. Previous viewers could read two separately specified files
and display them one after the other. The big advantage to this format is
the same as for stereo slide holders. You can set up both images just how
you want and they stay together in one file. The viewer reads the one file
and cuts it in half for the display process, which is frame sequential. 

*Interlaced* is where alternate pixel lines of one image carry alternate
left and right information. This method derives from video technology which
uses alternate lines in it's refresh cycle as standard. On the computer it
is not easy to get the display to interlace. Most modern monitors are
Non-interlaced. They refresh the entire screen each cycle. In fact some
systems, this includes video accelerator boards and monitors, cannot handle
interlacing the display itself. For sequential frame stereo the entire
screen is filled with a left image and immediately with the next screen
refresh, the entire screen fills with the right image. With hardware
acceleration this can happen up to 120 Hz (no flicker). Without hardware
acceleration, this is limited to 60Hz or less (visible flicker). Actual full
stereo image frequency is then half the vertical refresh rate.

The JPS file uses the full sized image pair and does not interlace them.
Interlacing throws away half of the image - a line carrying the left image
cannot carry the right image too. VRex software, and maybe other's, can read
the file and extract the interlacing lines as needed without interlacing the
image itself. This makes the format usable for everyone and optimizes the
quality available.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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