\section{Exercises}
\begin{footnotesize} 
\subsection*{Targeted exercises} 
\subsubsection*{Exercises for Section \ref{Understanding_how_computers_represent_images}} 
\begin{enumerate}\setcounter{enumi}{-1}
	\item  Create an array of 1s and 0s where the arrangement represents a picture of a frog.

\end{enumerate}
\subsubsection*{Exercises for Section \ref{Importing_and_manipulating_images_using_the_Pillow_library}} 
\begin{enumerate}\setcounter{enumi}{0}
	\item  Take a selfie.

	\begin{enumerate}
	\item Turn the selfie into black and white.
	\item Color all black parts red, and all white parts blue.
\end{enumerate}

\item  Using Pillow, combined with Numpy arrays, create a png image that is a smiley face.

\item  Take a selfie and crop out your body, much like you would do to create a headshot. 


\end{enumerate}
\subsection*{Comprehensive exercises} 
\begin{enumerate}\setcounter{enumi}{3}
	\item  One of the old lab members in your group made a .png figure of some spectra. You want to include this image in an analysis of your current data, and want to preserve the color scheme you are using in your publication. You don’t have access to their data anymore. Write a script that will go through any such images, and replace one color with another one. You can test with the file 'old-spectra.png' found on the companion website (\website).

	\item  You also think it could be good to extract the values from the old spectra discussed in the previous exercise.  You are lucky that the extremes of the $x$ and $y$ axes are labeled, so that you can simply crop the image to contain only the plot area and know the data values of the edges. This would let you re-plot this in any Plotly figure you want. Write a code that will crop this image, and then extract locations of the data and assign them the correct values. Save the extracted values to a .csv or excel workbook. Then plot the resulting data in Plotly. Comment on how well this worked for extracting the data.  Does the plot look similar?
\end{enumerate}
\end{footnotesize} 
