Kifu: Go game record (kifu) generator

Image change detection:

Using vertical and horizontal RGB components sums of a thresholded difference between a reference image and the current one,

it is easy to compute the screen coordinates of a played stone

Geometric projection:

It is necessary to map each point from a reference rectangle to a point in the displayed shape, or vice-versa;

without considering scene, camera or observer parameters.

The only data available are the corner coordinates on the projection plane and the reference rectangle proportions.

Grid intersection detection:

As the camera has not been calibrated, and the corner coordinates are detected from image change,

the projected coordinates will be somewhat approximative.

So it is necessary to detect the nearest grid intersection for each computed grid point.

Using the accumulative algorithm described above on a square portion of the rectifed image

around the computed intersection should be sufficient, but the result is maybe be more exact

doing line detection on the square edges to compute the intersection using line geometry laws.

Using the resulting grid(s) and the real size or proportions of the object(s) in the scene,

maybe it becomes possible to calibrate the camera with Tsai algorithms or others.

Stone detection:

When a stone is played it overlaps 1 grid square on a corner, 2 on the borders and 4 in the center.

Computing horizontal and vertical pixel sums for each grid cell can tell on which intersection

the stone is played and reveal the color of the stone, being darker or brighter than before.

Methods for mapping the coordinates:

"2.2 Perspective transformation with two vanishing points" (pages 2 and 3, equations 7 and 10)

Inverse homography and plane image rectification (page 14)

"Inferring Projective Mappings" (page 3)

Links:

irc://irc.freenode.net/#kifu

Photointerpretation and Small Scale Stereoplotting with Digitally Rectified Photographs with Geometrical constraints: http://cipa.icomos.org/fileadmin/papers/potsdam/2001-21-gf01a.pdf

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