This is an individual assignment. You must complete this lab on your own, although you may discuss lab concepts with other students. Please keep the Academic Integrity Policy in mind---do not show your code to anyone outside of the professors and ninjas, and do not look at anyone else's code for this lab. If you need help, please post a question on Piazza, or contact the professors or ninjas.
The goal of this lab is to introduce you to basic concepts in the C++ program language. Concepts you will be familiar with after this lab include:
Please access your lab by cloning the appropriate git repository, e.g.:
$ git clone firstname.lastname@example.org:CS35-s17/lab01-jbrody1.gitWe've given you a skeleton version of the program. Useful links:
This lab will have you write a program to load and output image files. In addition, you will provide a user the option to perform some basic image manipulation, including color alteration and horizontal flipping. To begin, we will first learn about the PPM Image format. Click here for information about the PPM format (and how to parse it) as well as tips for viewing and creating PPM image files.
Reading about the PPM format may seem overwhelming, but it's actually fairly simple to get started. You will write a program called picfilter which allows the user to manipulate PPM files. Your program will read a PPM file into memory as an array, perform a transformation on it, and then save it in another PPM file. Your program will ask the user to enter the name of the input PPM file, the name of the output PPM file, and the name of the transformation to perform.
$ clang++ -o picfilter picfilter.cpp image.cpp ppmio.cpp $ ./picfilter Welcome to the Portable Pixmap (PPM) Image Editor Enter name of input file: test_data/MachuPicchu.ppm Enter name of output file: test_data/MachuPicchu-gray.ppm Enter filter command: grayscale Image converted. Goodbye!The original and resulting image:
To read a PPM file, you will pass its filename to three functions:
The array of pixels may be larger than you'd expect; it will actually be three times the size of the number of pixels in the image. For instance, a 100x100 PPM image would produce an array of size 30,000. This is because each pixel is represented by three numbers: the amount of red, green, and blue light to show for the pixel. Each number ranges from 0 (no light) to 255 (all the light). Here are some example pixel values:
The read_ppm function takes care of opening a PPM file, reading the image data into it, and giving it back to you the array you provided. Once you've read the PPM, you can change it and then write it back out into another file using the corresponding write_ppm function. These functions are defined in ppmio.h.
Once you've read in your PPM as an array of integers, it's up to you to change those integers in any way you like. You could loop over the entire image and set every number to 255, resulting in a giant white rectangle (since every pixel is now white). You could loop over each position in the first row and set each third number to 0, draining all of the blue light from the top line of the image.
As mentioned above, the user specifies an input file, a transformation, and an output file. Here are the transformations the user is allowed to request:
For each of these transformations, you will write a void function of the same name that takes an int array containing a PPM image and makes the appropriate changes. You will then complete a main function which asks a user for the name of the input and output files, as well as the transformation to perform, loads the image, calls the right transformation function, and then saves the result. If the user gives an invalid transformation (e.g. flipDiagonal), your program should tell the user so and ask again for a valid transformation. Keep asking until the user enters a valid transformation. You are allowed to ignore errors caused when the user gives non-existent or invalid filenames.
Your starter code has been separated into several files:
To compile your program, clang++ will need to know about all three .cpp files. Make sure to include them in your compilation command:
$ clang++ -o picfilter picfilter.cpp image.cpp ppmio.cpp
Remember: you don't have to write everything all at once. It's often best to get a small amount of your code to work and then move on to the next part. You can follow these steps to complete your lab:
Start by completing your
main function. Much of
this code has been given to you -- we've already shown you how to
define an array for the ppm file, ask the user for input/output
file names, and read the file into an array. The starter file
also recognizes when a user asks for noRed and calls the
appropriate transformation function. First, you should add in
code that tells the user when they've entered an invalid
transformation, and you should write the transformed ppm image out
to the output file. For now, assume that noRed is the only
We've given you a function stub for noRed. This is an empty function definition that does nothing. At this point, you should be able to run picfilter, call noRed, and write the result out to a file; however, the output should match the input file. Next, implement noRed and verify that it removes all red from the input image.
One by one, implement more transformations, adding them
main as you complete them. Try each of them out
before you move on to the next one.
Once you've finished writing your transformations, run your program several times and compare it to the files in test_data to see if your transformations work correctly.
You can use ImageMagick, a package installed on the CS network, together with picfilter to edit your own images! Start by converting your picture to PPM format:
$ convert my_image.jpg -compress none my_image.ppm
Then, do anything you want with picfilter:
$ ./picfilter Welcome to the Portable Pixmap (PPM) Image Editor Enter name of input file: my_image.ppm Enter name of output file: my_image-gray.ppm Enter filter command: grayscale Image converted. Goodbye!
Finally, convert your new image back to some other format.
$ convert my_image-gray.ppm my_image_2.jpg
There! You've just used your homework assignment to perform photo editing on your own files. :)
To summarize the requirements of this lab:
Once you are satisfied with your code, hand it in using git.
Remember the add, commit, push development cycle. You can push
as many times as you like, but only the most recent submission will be
graded. You may want to run git status to confirm all modifications have been pushed.
This lab write up is based off of Joshua Guerin and Debby Keen's NIFTY 2012 submission titled PPM Image Editor.