Production of anaglyphs

A method for producing and anaglyph includes the steps of: producing a first image color record having at least two color numbers per pixel and representing the distribution of at least first and second image colors in one of the images of a stereo pair of images; producing a second image color record having at least one color number per pixel and representing the distribution of a least a third image color in the other of the stereo pair of images; combining the first image color record with the second image color record to produce an anaglyph color record having at least three color numbers per pixel, the three color numbers of the anaglyph color record corresponding to first, second and third anaglyph colors, and anaglyph color record representing the distribution of the anaglyph colors in the anaglyph.

The invention relates to a method for producing anaglyphs. 
In this specification, an anaglyph is defined as any two dimensional image 
which, when viewed through anaglyph spectacles, gives the appearance of 
being a three dimensional image. 
Anaglyph spectacles ar defined as any device which ensures that each eye of 
a person viewing the anaglyph receives from the anaglyph a different 
frequency distribution of light. 
Anaglyphs are conventionally formed from two photographs, or two motion 
films, which have been taken from slightly different positions, usually 
spaced laterally apart by a distance corresponding to the separation 
between a person's eyes, so as to produce two slightly different images, 
commonly referred to as a stereo pair of images, One of the images is 
usually coloured red and the other blue or green so that, when the two 
images are viewed through spectacles having one red lens and one blue 
lens, one eye sees one image and the other eye sees the other image, thus 
giving the appearance of depth. The two images are normally superposed. 
Computer-generated anaglyphs have also been formed by combining image data 
for two differently coloured monochrome images. An image may be stored by 
a computer in the form of a colour record. In this specification a colour 
record is defined as a sequence of numbers representing the colour 
distribution of an image. The image is divided into pixels, and the colour 
record contains a series of numbers, or groups of numbers, each number, or 
group of numbers, representing the colour of an individual pixel. A number 
of different formats are commonly used for such colour records, and the 
particular format employed depends to a large extent upon the amount of 
information which can be stored by the computer. Thus, computer using 8 
bits per pixel can use a maximum of 256 colours in any one image, whereas 
a computer using 24 bits per pixel can use up to 16,77,214 different 
colours. 
In some formats the colour record contains three separate numbers for each 
pixel of the image, the three numbers representing the respective amounts 
of three different colours present in the pixel. For example, in the 
"Truevision Targa-24" format the colour record had eight bits representing 
the amount of red in the first pixel, followed directly by eight bits 
representing the amount of green in the first pixel, then eight bits for 
the amount of blue in the first pixel, followed by 8 bits for the red in 
the second pixel, and so on for every pixel of the image. In this 
specification, such numbers are referred to as colour numbers. That is, a 
colour number represents the amount of a particular colour, usually one of 
three, in a particular pixel. The colour numbers need not represent the 
colours red, green and blue respectively, although red, green and blue 
have been found to be capable of producing an enormous range of colours, 
when combined in different proportions, and are therefore the most popular 
choice. Whichever format is used, it is always possible to transform the 
colour record to a different format, although if the new format uses fewer 
bits per pixel then some loss of colour range will usually occur. 
Anaglyphs produced by computer have been formed by combining image data for 
two differently coloured monochrome images so as to form a single image, 
i.e. an anaglyph, which can be displayed on a VDU. 
However, anaglyphs formed as described above, using either photography or a 
computer, where each original image is monochrome, have not been found to 
produce a particularly broad or realistic range of colours when viewed 
through anaglyph spectacles. 
SUMMARY OF THE INVENTION 
According to the invention there is provided a method for producing an 
anaglyph, the method including the steps of: producing a first image 
colour record having at least two colour numbers per pixel and 
representing the distribution of at least first and second image colours 
in one of the images of a stereo pair of images; producing a second image 
colour record having at least one colour number per pixel and representing 
the distribution of at least a third image colour in the other of the 
stereo pair of images; combining the first image colour record with the 
second image colour record to produce an anaglyph colour record having at 
least three colour numbers per pixel, the three colour numbers of the 
anaglyph colour record corresponding to first, second and third anaglyph 
colours, and the anaglyph colour record representing the distribution of 
said anaglyph colours in the anaglyph. 
The method may also include the step of displaying the anaglyph 
corresponding to the anaglyph colour record. 
It will be appreciated that the visual image resulting from viewing such an 
anaglyph through anaglyph spectacles may comprise colours produced by any 
combination of the three anaglyph colours. Therefore, such an image may be 
more colourful and/or realistic than images derived from conventionally 
produced anaglyphs. 
It will also be appreciated that the stereo pair of images need not 
correspond to any real physical object, and could, for example, be 
generated by a computer and, of course, the method according to the 
invention is particularly suitable for performance by a computer. 
Preferably, the three anaglyph colours are chosen so that no one of the 
three anaglyph colours can be formed by any combination of the other two 
anaglyph colours. 
It is also preferable that the three image colours are chosen so that no 
one of the three image colours can be formed by any combination of the 
other two image colours. 
Conveniently, the three image colours are chosen to be the same as the 
three anaglyph colours. 
In one embodiment of the invention, the first and second image colour 
records each have at least three colour numbers per pixel, the three 
colour numbers corresponding respectively to the three image colours. 
The method may also include the step of adjusting the values of the colour 
numbers corresponding to at least one of the image colours in at least one 
of the image colour records, preferably before the two image colour 
records are combined. 
For example, if the first image colour record contains colour numbers 
corresponding to the third image colour, then these colour numbers may be 
adjusted so that the third image colour is entirely, or almost entirely, 
removed from said one of said stereo pair of images. 
Additionally or alternatively, if the second image colour record contains 
colour numbers corresponding to the first image colour then these colour 
numbers may be adjusted so that the first image colour is entirely, or 
almost entirely, removed from said other of said stereo pair of images. 
Each colour number in the first image colour record corresponding to the 
second image colour may be adjusted so that the amount of the second image 
colour present in said one of said stereo pair of images is reduced by 
between 10% and 40%, or by between 20% and 30%, relative to the amount of 
the first image colour in said one of said stereo pair of images. 
If the second image colour record contains numbers corresponding to the 
second image colour, then these colour numbers may be adjusted so as to 
entirely, or almost entirely, remove the second image colour from said 
other of said stereo pair of images. 
Preferably, the step of combining the first and second image colour records 
includes calculating the average amount of each image colour present in 
corresponding pixels of the two images of said stereo pair of images, and 
assigning values to the colour numbers of the anaglyph colour record in 
such a way as to ensure that each pixel of the anaglyph contains an amount 
of each image colour equal, or substantially equal, to the average amount 
of the image colour present in the corresponding pixels of said two 
images. 
The steps of producing the first and second image colour records may 
include digitising images of an object, which images have been formed by 
any kind of electromagnetic radiation reflected from, or emitted by, the 
object. 
The invention also provides apparatus for performing any of the methods 
described above, the apparatus comprising digitising means for digitising 
information relating to the distribution of colours in a stereo pair of 
images, processing means for adjusting the colour numbers of the first and 
second image colour records, and for combining the first and second image 
colour records so as to produce the anaglyph colour record, and display 
means for displaying the anaglyph corresponding to the anaglyph colour 
record. 
The processing means may be a dedicated micro-processor, or a computer, or 
personal computer, set up to run a suitable program. 
The invention also provides, in a second aspect thereof, a method of 
encoding information by means of a stereo pair of images, wherein each 
image comprises an array of shapes, for example dots, the shapes being so 
arranged that, when the stereo pair of images is viewed through a 
stereoscope, some of the shapes appear to be closer to the viewer then the 
other shapes, the information being in alphanumeric form and being 
contained in the arrangement of the shapes which appear to be closer to 
the viewer, or of those shapes which appear to be further away from the 
viewer, and such information not being perceivable by viewing either image 
alone. 
A stereoscope is any device which enables one eye of the viewer to see only 
one image, and the other eye of the viewer to see only the other image, of 
a stereo pair of images. 
It will be appreciated that the encoded information stored by means of such 
a stereo pair of images could be revealed by means of a computer, without 
the need for a person to actually view the stereo pair of images, if the 
computer were to be provided with information relating to the two arrays. 
The invention also provides a stereo pair of images when produced by the 
above method. 
In one embodiment of the invention, the shapes of at least one of the 
images are arranged as a random array.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
One example of the invention will now be described. 
A stereo pair of images corresponding to two full colour photographs is 
stored in digital form by a computer in two image files. This can be done 
by using a so called "flat bed colour scanner" in known manner. The 
photographs are simply placed on the flat bed scanner, which then converts 
the information stored in the photographs into digital form. The two image 
files are stored in "Truevison Targa-24" format which uses 24 bits per 
pixel, 8 bits for red, 8 bits for green, and 8 bits for blue. 
Before the two image files are combined to produce an anaglyph, all of the 
colour numbers corresponding to green and blue in the second image file 
are set to zero, the colour numbers corresponding to red in the first 
image file are also set to zero, and the colour numbers corresponding to 
green in the first image file are reduced by 25%, i.e. by multiplying each 
colour number corresponding to green in the first image file by 0.75. 
The two image files are then combined using a program called "Average" 
which is part of a software package called "ImageTools" written by John 
Bridges. This software enables the two image files to be averaged to 
produce a single image file. That is, the single image file is generated 
by averaging the value of each colour number of each pixel in the first of 
the two image files with the value of the same colour number of the 
corresponding pixel in the second of the two image files. The resulting 
single file then corresponds to an anaglyph, in accordance with the 
present invention. 
The resulting anaglyph therefore contains a large range of colours formed 
from different combinations of red, green and blue. The anaglyph may be 
displayed on VDU, or colour printer, and viewed through a pair of anaglyph 
spectacles having one red filter and one cyan blue filter, to give an 
appearance of depth. 
It is not fully understood how the human brain combines the two images to 
produce the visual sensation of a multi-coloured image. It might be 
thought at first sight that, because the lenses are red and blue, only 
colours formed by combining the two colours red and blue will be observed. 
However, it has been found that a very large range of colours can be 
observed when the anaglyph is viewed through such anaglyph spectacles, and 
that the appearance of the anaglyph is very close to that of the original 
photographs, as regards colour. This may be due to the fact that the red 
and blue lenses let through a range of different colours in addition to 
red and blue. 
It will be appreciated that in the above method, since the colour numbers 
corresponding to green and blue in the second image file are set to zero, 
the same effect may be achieved by omitting such colour members from the 
second image file ab initio. The second image file will then contain only 
information relating to the red colour content of one of the images, and 
similarly the second image file may only contain information relating to 
the green and blue colour content of the other image. It follows, 
therefore, that image files suitable for generating an anaglyph could be 
formed by scanning one of the two photographs with the flat bed scanner 
set to receive and/or transmit one combination of colours, in this case 
only red, and by scanning the other of the two photographs with the flat 
bed scanner set to receive and/or transmit a different combination of 
colours, in this case blue and 75% green. Furthermore, it is possible to 
conceive of applications of the invention which allow an object which has 
been designed by, or with the aid of, a computer to be coloured by an 
operator. The computer could then create a stereo pair of image files, one 
containing only red colour numbers, and the other containing only green 
and blue colour numbers, which could then could be combined to form the 
image file of an anaglyph which would appear in full colour when viewed 
through anaglyph spectacles having a red and a blue filter. 
It will also be appreciated that, because it is possible to use different 
combinations of different colours to form the same colour, the three 
colours used in the image file for the anaglyph need not necessarily be 
the same as the three colours which are used in the two image files for 
the initial stereo pair of images, although it will usually be convenient 
to use the same three colours for all of the image files. 
Anaglyphs produced by the above method may be displayed on computers with 
colour display systems, or output via appropriate software and hardware to 
devices such as colour television screens, colour video printers, and a 
variety of colour hard copy devices; or they may be transferred, for 
example by modem, to sites where such equipment is available. Anaglyphs 
corresponding to stereo pairs of images taken from a wide variety of 
sources may be created by this method. Such sources include photographs, 
slides, photogrammetric images, medical images, and images created "de 
novo" using a computer. A monochrome stereo pair of images may be 
pseudo-coloured before being converted into anaglyphs in order to 
facilitate and enhance the interpretation or analysis of the anaglyph. 
Furthermore, a sequence of anaglyphs may be created to give the appearance 
of a moving subject. The invention has potential applications in the 
fields of, for example, photogrammetry (including mapping, satellite image 
analysis, and oil exploration), medicine, natural science, computer aided 
design, architecture, archaeology, meteorology, entertainment and defence. 
Furthermore, all that is required in order to perform the method is a 
personal computer with a suitable colour display system and a pair of 
anaglyph spectacles.