Phantogram builder

Temporary quick help to start

07/09/2004

Thanks to Steve Boddy for his help about how to build a phantogram, and his cup example.

Top left : the dotted triangle is what you see when looking at the anaglyph, taken with a horizontal camera, viewed on a vertical print.

D is the distance to take into account to evaluate the stereo base (with the common rule : base = 1/30 x D).

Top right : the dotted triangle is what you see when looking at the anaglyph, taken with a 45°camera, viewed on a 45° print.

D is the distance to take into account to evaluate the stereo base (with the common rule : base = 1/30 x D).

Bottom : the phantogram builder of AnaBuilder (and the method that is explained below) is calculating from one of the top anaglyphs

the anaglyph that should be printed to see exactly the same dotted triangle when this new anaglyph is viewed with a 45° angle.

2) put this paper on a table with an object on it.

3) take a stereo couple of this object from a point of view making an angle of 45° with the horizontal. The stereo base should be centered with the object. When doing this, the regular square grid appears as perspective, having the nearest squares larger than the furthest.

4) load the stereo view in AnaBuilder, and call the menu "tools/Experimental/Phantogram builder", it opens a new window with the left/right views being distored to reduce the perspective effect on the square grid. The goal now is to tune the values to get back a well-regular square grid, in order to perfectly reverse the perspective effect. After having changed the values, click on "View" button to calculate the new distortion, and "Export" button to view the result in AnaBuilder. This can be done several times, till having the best square grid as possible.

5) when this is obtained, change the resolution of the image to get a better quality, and export to final stereo in AnaBuilder. Save it.

6) print the stereo as anaglyph and put it on a table. Look at it with the same point of view as the original one. The object should seem to stand over the table as the original.

Example with a perfect calculated image from Steve Boddy :

Left image :

Right image :

Phantogram obtained with values :

r = 42.5

xLeft = xRight = 0

z = 1.5

fov = 50

y/x = 2.0

1024x1024 image, (cropped afterward in AnaBuilder)

Right image :

Phantogram obtained with values :

r = 42.5

xLeft = xRight = 0

z = 1.5

fov = 50

y/x = 2.0

1024x1024 image, (cropped afterward in AnaBuilder)

Here is a natural shot example (sorry for the little curve of the chess board at the top, but the table was too short : the pliable check board is a little bulging) :

Crossed view of the original (without horizontal left/right adjustment) :

Phantogram obtained with values :

r = 52.5

xLeft = 3

xRight = 0

z = 1.5

fov = 40

y/x = 2

1024x1024 image, (cropped afterward in AnaBuilder)

Phantogram obtained with values :

r = 52.5

xLeft = 3

xRight = 0

z = 1.5

fov = 40

y/x = 2

1024x1024 image, (cropped afterward in AnaBuilder)

r is the reversion angle. It is by default set to 45°, so that the front squares of the grid become smaller, and the back squares of the grid become larger. When r is decreased the reversion effect becomes smaller. When r is increased the reversion effect becomes larger.

xLeft is an horizontal displacement of the left view. It is set to zero by default. When xLeft > 0 the left view is tilt to the left. When xLeft < 0 the left view is tilt to the right.

xRight is an horizontal displacement of the right view. It is set to zero by default. When xRight > 0 the right view is tilt to the left. When xRight < 0 the right view is tilt to the right.

fov is the size of the field of view. It is set to 70° by default. When fov is increased, the views are zoomed out without distortion. When fov is decreased, the views are zoomed in without distortion.

y/x enables to tune the horizontal/vertical ratio to make a rectangle grid to become a square grid.

z is a distance to the view. Changing it is equivalent to combining a r changing and a fov changing together.