Basic Concepts of Stereoscopic Image Table of ContentsBackPreviousNext

Because our two eyes are separated by a distance, when we are looking at an object, each eye see a different image of the object.  This is even more obvious when we are looking at a close object.
 


Object viewed
by a camera


Object viewed
by our left eye


Object viewed
by our right eye

To create the illusion of a real object on a screen, we need to display on the screen the left and right images simultaneously, and we also need to find a way to avoid our left eye seeing the right eye image and our right eye seeing the left eye image.  The four most used techniques are Red Blue Anaglyph Image with Red Blue Glasses, Interlaced Image with Liquid Crystal Shuttle Glasses, Polarized Monitor with Polarized Glasses and VR-Helmet/Head Mounted Device.  For more information about the last three (expensive) techniques, search the Web (or try this link).

The Red Blue Anaglyph Image Technique is based on the nature of a color display cell.  Each color display cell consists of three small lights: red, green and blue.  Each light intensity can vary independently from the two others.  The light intensity varies from 0 to 255 to gives 256 levels of intensity for each of the three lights for a total of 16,777,216 (256 x 256 x 256) possibilities.  Because a color display cell is so tiny, our eyes see the red, green and blue lights as if it was only one light of a specific color among 16,777,216 different colors.

A zoomed display cell may looks like that : 

Example of stacked cells with light intensity
varying from 0 (bottom) to 255 (top).
The three lights use the same intensity here. 

Example of what your eyes see
when looking at the previous
stacked cells example.

The Red Blue Anaglyph Image Technique consists of using only the display cells' red light for displaying the left image and the display cells' green and blue lights for displaying the right image.  So each display cell of a Red Blue Anaglyph image is created by using the display cells' red light of the left image, and the display cells' green and blue lights of the right image.  When using Red Blue Glasses, the red lens on the left eye black out the display cells' green and blue lights so only the left image is visible by the left eye.  The blue (or cyan) lens on the right eye black out the display cells' red light so only the right image is visible by the right eye.


Colored left image with
all display cells' green and
blue lights turned off


Colored right image with
all display cells' red light
turned off


Colored left and right images
mixed together to form a
Pseudocolor Red Blue Anaglyph image


Grayscale left image with
all display cells' green and
blue lights turned off


Grayscale right image with
all display cells' red light
turned off


Grayscale left and right images
mixed together to form a
Grayscale Red Blue Anaglyph image

In some circumstances, Pseudocolor Red Blue Anaglyph image can be very hard for the eyes when looking at it.  That happens when big regions in the image use a color composed with almost no red light or no green and blue lights.  In such cases, the left image or right image will have black regions with no detail because of the way the Red Blue Anaglyph Image Technique works.

The alternative is to use Grayscale Red Blue Anaglyph Image instead.  The only difference in the technique consists on converting the left and right images to grayscale images before turning off the unwanted lights.  A gray level is calculated by taking the average intensity of the red, green and blue lights and then resetting the intensity of the red, green and blue lights to this average intensity value.  When the red, green and blue lights use the same intensity, the resulting color is a grayscale.  By doing this, each of the three lights now hold the same image detail.  When some lights are turned off by the technique, you are always sure that at least one of the three lights is still holding a pertinent image detail instead of a zero value.

Example of an object
with problematic colors
viewed by a camera.


Colored left image with
all display cells' green and
blue lights turned off


Colored right image with
all display cells' red light
turned off


Colored left and right images
mixed together to form a
Pseudocolor Red Blue Anaglyph image


Grayscale left image with
all display cells' green and
blue lights turned off


Grayscale right image with
all display cells' red light
turned off


Grayscale left and right images
mixed together to form a
Grayscale Red Blue Anaglyph image

NOTE:  People use the term Red Blue Anaglyph but in facts the two colors are Red and Cyan (green + blue = cyan).  So if you are looking for Red Blue Glasses, you better purchase Red Cyan Glasses for brighter image.  If you want to see Pseudocolor Red Blue Anaglyph images, you must use Red Cyan Glasses otherwise the blue lens of a Red Blue Glasses will also black out the display cells' green light.


Below is a simulation of a transparent stereoscopic .MNG image over a
background image with a display mode set to Pseudocolor Red Blue Anaglyph.


Click here for a bigger .GIF animation with white background.

Click here a full screen capable .AVI animation.
 

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