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I'm looking for a generic algorithm to calculate a red/cian anaglyph starting from the original image and his b/w depth map (example: http://www.swell3d.com/2008/07/turn-2d-painting-into-3d-anagl.html)

That algorythm are used, for example, in Photoshop but I can't find a readable explanation to reproduce it.

Thanks

TheUnexpected
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    Related: http://stackoverflow.com/questions/4720857/how-to-create-3d-streoscopic-images-using-matlab-with-image-tool – mpenkov Oct 10 '11 at 16:28

3 Answers3

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After some researches I found what I was looking for. First, I've readed some Photoshop/Gimp tutorials that describes how to make anaglyphs from two inputs: an image and its grayscale depth map. The core of the process is the use of "Displace Tool" and the depth map as a displacement map. One of the several youtube tutorials: http://www.youtube.com/watch?v=gfYMe_vYhu4

So, I took some documentation about Gimp's Displace Tool by looking at this http://docs.gimp.org/en/plug-in-displace.html and directly at the source code of the tool (the method is very similar to the one proposed by Asgeir).

This lets us to produce two stereo images from the input, by looking at the depth map. The red and cyan colors of every image are calculated by reading this page http://3dtv.at/Knowhow/AnaglyphComparison_en.aspx ("Optimized" matrices are the best ones).

Then, the sum of the two images in one will produce the final anaglyph. Thanks everybody.

TheUnexpected
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There are two algorithms involved. The first uses the original image and the depth map to produce a left and a right image. The second combines these images into a red-cyan anaglyph.

There are a couple ways to accomplish the first part. One is to take the original image and texture map it onto a fine mesh that lies flat in the XY plane. Then you tweak the Z values of each vertex in the mesh according to the corresponding value in the depth map. You've basically created a textured bas relief. You then use a 3D rendering algorithm to render the image from two vantage points that are offset horizontally by a small amount (essentially from the vantage point of a person's left and right eyes as they would view the bas relief).

There is probably a way to directly shift the pixels left and right which is a good fast approximation to what I described above.

Once you have the left and right images, you pass one through a cyan filter and one through a red filter. If you have RGB sources, that's as simple as taking the red channel from one image and combing it with the green and blue channels from the other image.

Anaglyphs work best with muted colors. If you have strong primaries, it won't look as good. You can use an algorithm to reduce the color saturation of the original image before you begin.

Adrian McCarthy
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  • Really, really interesting. I'm assuming that the first involved algorithm is the hardest part and, yes, there is probably a way to shift the pixels left and right by directly reading darker/brighter zones of the depth map. I'm looking for this method, because the one you described that renders a 3d mesh seems good but too much sophisticated for my needs. The second step is easier, I've already picked some websites that show lots of different color adjustments for better rendering. Thanks so much for now, but i'm on the 50% of the work :) – TheUnexpected Oct 10 '11 at 17:29
  • Obviously, if you can post some useful links about the first step they will be appreciated – TheUnexpected Oct 10 '11 at 17:35
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From the description in the link you provided I would assume that it is something like

for each pixel in depthmap
    x_offset = (depthmap[x][y] / 255.0f) * MAX_PIXEL_OFFSET * DIRECTION
    output[x + x_offset][y] = color_buffer[x][y]

blend output with color_buffer

Where MAX_PIXEL_OFFSET is the maximum shift in pixels and DIRECTION is -1 for one color and 1 for the other. This is assuming that the depthbuffer is one byte per pixel, range [0..255] and that 0 in the depthbuffer represents maximum distance.

Asgeir
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