[photo-3d] Re: 3d shutter glasses / mac / VR-joy

[Andrew Woods <A.Woods@xxxxxxxxxxxxxxxxxx>]

Jeff Ahn wrote:
>However, you can use VRJoy with Mac as long as the Mac has 15pin VGA
>output(I think PowerMac series has it). Only you have to do is making an
>"Interlaced image".

Let me step in here with a word on terminology.

"Interlaced Image" in an ambiguous term and in this case I think
is causing Boris some confusion.

I this case I think Jeff is referring to what I & others prefer to call a
row-interleaved 3D image - i.e. alternate rows of the image are left 
and right image.  

i.e.  LLLLLLLLLLLLLLLLLLLLLLLL
      RRRRRRRRRRRRRRRRRRRRRRRR
      LLLLLLLLLLLLLLLLLLLLLLLL
      RRRRRRRRRRRRRRRRRRRRRRRR
      LLLLLLLLLLLLLLLLLLLLLLLL
      RRRRRRRRRRRRRRRRRRRRRRRR
      LLLLLLLLLLLLLLLLLLLLLLLL
      RRRRRRRRRRRRRRRRRRRRRRRR   

        e.g. http://info.curtin.edu.au/~iwoodsa/gallery/curtin01.gif

A row-interleaved 3D image can be in jpeg, gif, tif, etc format and
be displayed on an interlaced or progressive scan display.
VREX's Depthcharge can also convert jps images into row-interleaved format.

This introduces the other usage of the term interlaced when used for
video displays.  An interlaced display first "paints" the odd numbered 
lines and once these are finished, it "paints" all of the even numbered
lines.  These odd lines make up the odd field and the even lines make
up the even field.  

The opposite of interlaced is progressive, whereby all of the lines
are "painted" in one go on every update of the display.  (I should
point out I'm talking about CRT displays here).

The video mode (interlaced or progressive) is determined by the 
computer's video card.  Sometimes the user is given the option to
choose whether the display is in interlaced or progressive mode but
some video cards don't support interlaced at all.

Now, if a row-interleaved 3D image is displayed on an interlaced
display, it will produce a field-sequential 3D image (also known
as alternate field) that can be viewed in 3D with LC shutter glasses.

But, if a row-interleaved 3D image is displayed on a progressive
display, the resultant image cannot be viewed in 3D with normal
3D shutter glasses.  Both left and right image pixels are updated
every screen refresh so you don't have left and right images displayed
on alternate fields - needed for LC shutter glasses.

However, there is a special type of LC shutter glasses which provide
a function called line-blanking which will allow row-interleaved
3D images to be viewed in 3D while using a progressive video mode.  
The line-blanking shutter glasses actively blank out alternate
lines on alternate screen refreshes to create a pseudo interlaced
display.  The glasses have a dongle which fits between the video
card output and the video monitor.  On the first image refresh
the dongle blanks or blacks out the even numbered lines, thus 
only displaying the odd numbered lines.  In the next image refresh
the dongle blacks out the odd numbered lines, thus only displaying
the even numbered lines.  This cycle is repeated and hence a 
pseudo field-sequential 3D image is created.  Now it is important
to point out that the video display isn't really interlaced since
all the lines are still scanned - it's just that half of them
are blacked out.  A pair of LC shutter glasses are then connected 
to the dongle and are switched in time with the alternate images
so you can see 3D.

Line-blanking LC shutter glasses are a recent introduction - something
that's only appeared on the market in the last 3 or 4 years.
Some of the glasses from IO-Display, VREX, VR-Standard, and Tetratel
support line-blanking.

Boris wrote:
> Do the VR-joy glasses come with software that can take stereo pair stills
> (either as a single file or as a pair of files) and display them interlaced
> on the Mac monitor?  (VREX Depthcharge does this on the PC side, but not on
> Mac).
> 
> If I understand this correctly, the VR-joy glasses need only to read the
> signal going to the monitor to synch up properly?  I assume you have some
> kind of a splitter plug?  That would be fine, but does the mac still need a
> driver software to put this interlaced format on the screen?

The beauty of the line-blanking glasses is that you don't need special
drivers for your specific video card - part of the reason that Macs
have received little support.

All you need to do is display a row-interleaved image on your normal 
progressive display (progressive is the normal mode these days) and
the line-blanking glasses do their magic.

In fact you can display a row-interleaved 3D image right now in your
web browser by clicking on this link:
  http://info.curtin.edu.au/~iwoodsa/gallery/curtin02.gif

So, to answer Boris's final question, no you don't need any special
software to display a row-interleaved image on the screen, but you
will need something to create row-interleaved 3D images.  Maybe
the stereoscopic java applet.  http://www.stereophotography.com

Cheers,
Andrew.

 

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