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Open Source Computer Vision Library
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44 lines
1.5 KiB
44 lines
1.5 KiB
14 years ago
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\section{Basic operations with images}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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% %
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% C++ %
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% %
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\ifCpp
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\subsection{Input/Output}
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Load an image from a file:
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\begin{lstlisting}
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Mat img = imread(filename);
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\end{lstlisting}
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If you read a jpg file, a 3 channel image is created by default. If you need a grayscale image, use:
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\begin{lstlisting}
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Mat img = imread(filename, 0);
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\end{lstlisting}
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Save an image to a file:
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\begin{lstlisting}
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Mat img = imwrite(filename);
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\end{lstlisting}
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\subsection{Accessing pixel intensity values}
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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:
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\begin{lstlisting}
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Scalar intensity = img.at<uchar>(x, y);
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\end{lstlisting}
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\texttt{intensity.val[0]} contains a value from 0 to 255.
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Now let us consider a 3 channel image with \texttt{bgr} color ordering (the default format returned by imread):
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\begin{lstlisting}
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Scalar intensity = img.at<uchar>(x, y);
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uchar blue = intensity.val[0];
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uchar green = intensity.val[1];
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uchar red = intensity.val[2];
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\end{lstlisting}
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\fi
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