Manapouri Power Station

Lake Manapouri power station is deep underground. Tourists reach it by first taking a boat trip along Lake Manapouri and then riding a bus down a spiral road, tunneled into the rock of Fiordland.

Water leaves the turbines in two tunnels. At first only one tunnel was cut, but recently a second has been added to reduce the water resistance in the outflow and this has made the turbines much more efficient. The fresh water from the tunnels joins the salt water sea in Doubtful Sound, pictured here as an anaglyph.

At the time of this stereoscopic photograph, the turbines were being refurbished. Originally painted orange, they are now blue and this is a much better colour for anaglyph 3D. In fact the colour through red/cyan glasses is almost true.

If you do not have red/cyan 3D goggles, this page will make no sense.

Come back when you find some because there is some pretty heavy information about colour vision below here.

Manapouri underground Power Station, in 3D

Photography by John Wattie, March 2005

Technical stuff about anaglyphs

Parallax

For those with technical interest in 3D, an anaglyph gives an excellent depiction of stereoscopic parallax when viewed without the red/cyan goggles.

Look at the flood-lights. You will see a red and a cyan version. The difference between the two versions is the stereoscopic parallax.

Note where the two colours super-impose to make a white light. This is zero parallax.

In front of zero parallax, the red light is to the right of the cyan light. This is the opposite of the colours of your goggles (when you hold them the correct way round). This is negative parallax. The lights are in air space, in front of the computer screen when viewed in 3D.

Behind zero parallax, the red light is to the left of the cyan light. That is positive parallax. The separation gets greater the deeper we go into the tunnel until maximum separation on the back wall, below the crane gantry. That is still not stereo infinity, because the tunnel is not long enough for that. Positive parallax is in screen space, when viewed in 3D.

Viewed in 3D, the front turbine lies in front of the stereo window, and in front of the computer screen. It does this from the blttom of the frame and so is tolerable. When setting up anaglyphs there is a recomendation the window should be set at the zone of interest. This means the cyan and red images are superimposed and the colour is pretty near normal when seen without the goggles. This may violate stereo window, but "the ordinary citizen does not care much about that". Now I do not agree with this, but I can see the practical nature of it and so have used that system here. It works as long as you just use it gently and do not allow too much negative parallax at the window edges.

Colour distortion in an anaglyph

In this case the second turbine down has been chosen for zero parallax when setting up the anaglyph. Without the 3D goggles it looks a bit purple instead of blue. That is because the red channel (left eye) was set up to include information from all the colours from the left shifted photograph, since that makes the anaglyph show more detail. Often red does not tell you the full story about a scene. But it makes more subtle sense than that - so read on!

So the left eye is actually seeing the luminance of the whole scene, changed to red. When it sees the anaglyph through the red filter, the left eye now interprets the information as grey and colourless. Since the left eye is going to interpret the filtered light as grey, it makes sense to include all the grey information for the left eye.

Now, if we remove all colour information and use only luminence for the right eye, then turn it cyan (or blue, or green) instead of red, the left eye still thinks it is seeing grey. This complicated paradox is illustrated below.

The right eye is seeing blue and green information (cyan), but no red. Fortunately this power station is mainly coloured blue and green, so those two are rendered pretty well and the lack of red is of little concern.

In fact the purple colour of the turbines returns to its correct blue, when seen through the goggles. This is because the cyan filter removes the extra red we artificially introduced into the unfiltered picture, by including all colours in the red channel.

Example

Below here we have the right and left photographs in true colour. The right image is also presented monochrome. Then the fun begins.

If you fuse the stereo pairs while not wearing filters, the top pair are in true colour.

The middle pair are still in colour when fused, and are in 3D, but the colour intensity is reduced.

Now with the red/cyan goggles on, fusing the middle pair results in a grey stereo picture. The red filter converts everything to black and white, so both the left and right eyes see grey.

The anaglyph shows distorted colour. You decide if it is "near enough".

X format

For those who can only see stereo cross-eyed, here are the above pairs in X format.

The surprise is in the bottom pair of 3D images, when viewed cross-eyed, while wearing red/cyan anaglyph goggles.
The right eye only sees grey, no surprise.
The left eye also sees grey through the red filter and the fused stereoscopic image is monochrome.

The top pair of images are in nearly true colour through anaglyph glasses and when viewed cross-eyed to produce 3D, the fused image is still in colour.

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