Rendering stereo for posters

It is generally not a good idea to simply enlarge a stereo image for which the parameters have been derived for screen viewing. The risk is that the distance between the two images representing far away objects will expand to larger than the eye distance and in this case, people won't be able to view the image in stereo because they won't be able to focus on distant objects.

Before sending the rendered anaglyph image to the printer, it is better to manually build the CMYK file that will be printed. First render in red-green (exact). Then in photoshop, load the stereo image and make a new image the same resolution as the stereo image. Change this image to CMYK. Copy the green channel from the stereo image into the magenta channel of the new image and copy the red channel of the stereo image into the cyan channel of the new image. Leave the yellow and black channels white.

NOTE: Do not use the photoshop automatic conversion from RGB to CMYK because this will mix the channels and render the poster unusable. Likewise, if you send the printer your RGB file, they will likely convert the channels to CMYK by using an automatic conversion which will not produce the right results.

A note about focal length

It is often tempting to reduce the focal length in order to obtain more foreshortening and more depth effects. This is often used in drawings and on TV shows and we are so used to it that we come to feel like if there was no perspective when we view an image with more normal focal length.

While it is quite possible to do that for stereo rendering, it must be used with caution.

Keep in mind that the visual system relies on its experience of viewing the reality to interpret and decode the depth information in stereo images. For certain persons, it is already quite difficult to decode stereo images because their eyes must adapt to the viewing angle that provide depth information while still keeping the focus at the fixed screen distance which contradict the angle information. Introducing more distortion into the image will simply eliminate more people from appreciating your 3D stereo masterpieces.