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Diffstat (limited to 'day1/session5.tex')
| -rw-r--r-- | day1/session5.tex | 128 |
1 files changed, 116 insertions, 12 deletions
diff --git a/day1/session5.tex b/day1/session5.tex index fcbe031..554d53d 100644 --- a/day1/session5.tex +++ b/day1/session5.tex @@ -51,7 +51,7 @@ \setcounter{time}{0} \newcommand{\inctime}[1]{\addtocounter{time}{#1}{\tiny \thetime\ m}} -\newcommand{\typ}[1]{\texttt{#1}} +\newcommand{\typ}[1]{\lstinline{#1}} \newcommand{\kwrd}[1]{ \texttt{\textbf{\color{blue}{#1}}} } @@ -78,7 +78,7 @@ \author[FOSSEE] {FOSSEE} \institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay} -\date[] {30 April, 2010\\Day 1, Session 5} +\date[] {SciPy 2010, Introductory tutorials\\Day 1, Session 5} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %\pgfdeclareimage[height=0.75cm]{iitmlogo}{iitmlogo} @@ -132,7 +132,7 @@ plot(l, t, '.') \end{block} \end{columns} \begin{block}{Problem Statement} - Tweak above code to plot data in file `pos.txt'. + Tweak above code to plot data in file \typ{pos.txt}. \end{block} \end{frame} @@ -180,8 +180,8 @@ In []: plot(x, y) \begin{block}{Damped Oscillation} \tiny \begin{lstlisting} -In []: x = linspace(0, 4*pi) -In []: plot(x, exp(x/10)*sin(x)) +In []: t = linspace(0, 4*pi) +In []: plot(t, exp(t/10)*sin(t)) \end{lstlisting} \end{block} \end{columns} @@ -189,7 +189,8 @@ In []: plot(x, exp(x/10)*sin(x)) \begin{frame}[fragile] \frametitle{Problem 3 cont...} -Create a sequence of images in which the damped oscillator($e^{-x/10}sin(x)$) slowly evolves over time. +Create a sequence of images in which the damped +oscillator($e^{-t/10}sin(t)$) slowly evolves over time $t$. \begin{columns} \column{0.35\textwidth} \includegraphics[width=1.5in,height=1.5in, interpolate=true]{data/plot2} @@ -201,7 +202,7 @@ Create a sequence of images in which the damped oscillator($e^{-x/10}sin(x)$) sl \begin{block}{Hint} \small \begin{lstlisting} -savefig('plot'+str(i)+'.png') #i is int variable +savefig('plot'+str(i)+'.png') #i is some int \end{lstlisting} \end{block} \end{frame} @@ -209,11 +210,12 @@ savefig('plot'+str(i)+'.png') #i is int variable \begin{frame}[fragile] \frametitle{Problem 4} \begin{lstlisting} -In []: x = imread('smoothing.png') +In []: x = imread('smoothing.gif') In []: x.shape Out[]: (256, 256) In []: imshow(x,cmap=cm.gray) - \end{lstlisting} +In []: colorbar() +\end{lstlisting} \emphbar{Replace each pixel with mean of neighboring pixels} \begin{center} \includegraphics[height=1in, interpolate=true]{data/neighbour} @@ -250,14 +252,116 @@ y[1, 1] = x[0, 1]/4 + x[1, 0]/4 \frametitle{Solution} \begin{lstlisting} In []: y = zeros_like(x) -In []: y[1:-1,1:-1] = x[:-2,1:-1]/4+ - x[2:,1:-1]/4+ - x[1:-1,2:]/4+ +In []: y[1:-1,1:-1] = x[:-2,1:-1]/4 + + x[2:,1:-1]/4 + + x[1:-1,2:]/4 + x[1:-1,:-2]/4 In []: imshow(y,cmap=cm.gray) \end{lstlisting} \end{frame} +\begin{frame}[fragile] + \frametitle{Problem 4 cont\ldots} + \begin{itemize} + \item Apply the smoothing operation repeatedly to the original + image + + \item Subtract the smoothed image from the original to obtain + the edges + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Problem 5} + + What if you did the following in problem 4? + \begin{lstlisting} +In []: y1[1:-1,1:-1] = (x[:-2,1:-1] + + x[2:,1:-1] + + x[1:-1,2:] + + x[1:-1,:-2])/4 + \end{lstlisting} + + Are the answers different? + +\end{frame} + +\begin{frame}[fragile] + \frametitle{Problem 5 cont\ldots} + Why? The answer lies in the following: +\begin{lstlisting} +In []: x.dtype +Out[]: dtype('uint8') + +In []: print x.itemsize +1 + +In []: z = x/4.0 + +In []: print z.dtype +float64 + +\end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Problem 5 cont\ldots} +What if you did this? + +\begin{lstlisting} +x = imread('smoothing.gif') +y2 = zeros_like(x) +y2[1:-1,1:-1] = x[:-2,1:-1]/4. + + x[2:,1:-1]/4. + + x[1:-1,2:]/4. + + x[1:-1,:-2]/4. +\end{lstlisting} +\begin{itemize} + \item Will the answer be any different from \typ{y}? + \item What will the dtype of \typ{y2} be? + \item Discuss what is going on! +\end{itemize} + +\end{frame} + +\begin{frame}[fragile] + \frametitle{Problem 5 cont\ldots} + Did you do the right thing to find the edges earlier in problem 4? Fix it! + + Note that: +\begin{lstlisting} +In []: print x.dtype +uint8 +In []: x1 = x.astype('float64') +In []: print x1.dtype +float64 +In []: print x.dtype.char +d +In []: x.dtype.<TAB> # Explore! +\end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Problem 6} + + Edge detection looks much nicer with \typ{lena.png}, try it! The + gotcha is that it is a 4 component RGBA image with elements in the + range $[0.0, 1.0]$. + +\begin{lstlisting} +In []: x = imread('lena.png') + +In []: print x.shape +(512, 512, 4) + +In []: print x.min(), x.max() +0.0 1.0 +\end{lstlisting} + + Repeat the edge detection with this image. + +\end{frame} + \end{document} |