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added missing contrib & legacy chapters to the reference manual; fixed (x, y)->(y, x) ordering in Mat.at (ticket #1726)

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Vadim Pisarevsky 2012-04-10 14:28:48 +00:00
parent f5d327362b
commit c0000f3aed
2 changed files with 11 additions and 5 deletions
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14
doc/user_guide/ug_mat.rst
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@ -35,25 +35,29 @@ Accessing pixel intensity values
In order to get pixel intensity value, you have to know the type of an image and the number of channels. Here is an example for a single channel grey scale image (type 8UC1) and pixel coordinates x and y: ::
Scalar intensity = img.at<uchar>(x, y);
Scalar intensity = img.at<uchar>(y, x);
``intensity.val[0]`` contains a value from 0 to 255. Now let us consider a 3 channel image with ``BGR`` color ordering (the default format returned by ``imread``): ::
``intensity.val[0]`` contains a value from 0 to 255. Note the ordering of ``x`` and ``y``. Since in OpenCV images are represented by the same structure as matrices, we use the same convention for both cases - the 0-based row index (or y-coordinate) goes first and the 0-based column index (or x-coordinate) follows it. Alternatively, you can use the following notation: ::
Vec3b intensity = img.at<Vec3b>(x, y);
Scalar intensity = img.at<uchar>(Point(x, y));
Now let us consider a 3 channel image with ``BGR`` color ordering (the default format returned by ``imread``): ::
Vec3b intensity = img.at<Vec3b>(y, x);
uchar blue = intensity.val[0];
uchar green = intensity.val[1];
uchar red = intensity.val[2];
You can use the same method for floating-point images (for example, you can get such an image by running Sobel on a 3 channel image): ::
Vec3f intensity = img.at<Vec3f>(x, y);
Vec3f intensity = img.at<Vec3f>(y, x);
float blue = intensity.val[0];
float green = intensity.val[1];
float red = intensity.val[2];
The same method can be used to change pixel intensities: ::
img.at<uchar>(x, y) = 128;
img.at<uchar>(y, x) = 128;
There are functions in OpenCV, especially from calib3d module, such as ``projectPoints``, that take an array of 2D or 3D points in the form of ``Mat``. Matrix should contain exactly one column, each row corresponds to a point, matrix type should be 32FC2 or 32FC3 correspondingly. Such a matrix can be easily constructed from ``std::vector``: ::

2
modules/refman.rst
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@ -19,4 +19,6 @@ OpenCV API Reference
photo/doc/photo.rst
stitching/doc/stitching.rst
nonfree/doc/nonfree.rst
contrib/doc/contrib.rst
legacy/doc/legacy.rst