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COMP 273
Assignment 3

Things to consider
• Welcome to Assignment 3! We will be going through some fun image manipulation exercises
in this one, developing some tools for your image processing toolbox. You may notice that
FILE I/O will receive no partial marks. The reason for this is that every following question
depends on FILE I/O functioning.
• Make sure to follow conventions! beyond just readability and consistency between developers,
the conventions also help developers avoid hours of debugging. If you have questions about
conventions/debugging, feel free to ask any of the TAs.
• Even if your code does not produce the right image, make it produce something!
• You will receive a 0 on the question if the code does not compile.
• We will be using our own input files during grading, but the general structure is pretty
straight forward.
• Do not change any labels in the templates. You may add whatever extra labels you
may need, but use the ones provided as intended.
• Make sure you read all the questions first. Though some things you can get away with by
hard coding, this isn’t the case for all questions. Certain things (like moving through a 2D
matrix) are necessary in multiple questions, for example, and avoiding hard coding might
save time in the long run!
• File I/O is the only part of the assignment that requires error checking.
-MARS uses relative paths to find images. This means, if you have Mars in the same folder
as your .txt and scripts, then the paths specified in the templates will work accordingly.
• GIMP is an image editing software. Though you can use anything you’d like, its software
that can be used to view the .pgm file after generating the image is complete.
https://www.gimp.org/
• headers for .pgm files have a specific format.
P2(which is grayscale)
1
width height
## (max value)
http://netpbm.sourceforge.net/doc/pgm.html contains more information about proper .pgm
formatting. We’re concerned with PLAIN pgm, so we will assume that there are no comment
lines in the pgm file.
• You may use as many sub routines as you like! I.E. They must not be called from the main
function.
• You may add any extra .data you like, but make sure its after the specified line. The data
specified in the templates should be used accordingly.
1 FILE I/O (15 marks) No partial marks
(10 marks) The template for this question is provided in fileio.asm
(a) Using the template fileIO.asm as a starting point, write a MIPS procedure readfile that
takes as its argument the address of a string that contains a valid filename, and then uses
appropriate syscalls to read from that input file and then simply prints the content of that
file to the screen. In the template there are two input files called test1.txt and test2.txt
which you should test. To accomplish this task we allow you to create a large buffer, i.e., one
that is larger than the expected number of ASCII characters (bytes) in the input file. The
body of your code should work by calling the procedure you have written. The procedure
should open the file, read its content as ASCII characters, store the content in the buffer,
print the content to the screen, and then close the file. For your reference a more complete
set of MIPS syscalls implemented in MARS, along with clear documentation on how to use
each, is here: http://courses.missouristate.edu/kenvollmar/mars/help/syscallhelp.html.
(b) We shall now build on the above example. Following the process of reading the file test1.txt,
after which the ASCII characters have been read into the buffer, we shall call a second MIPS
procedure called writefile. This procedure should open a file called copy.pgm, should then
write the following information to that file:
P2
24 7
15
Then it should write out the content that was read into the buffer. It should then close the
file.
***(5 marks)Error statements should be printed if there are any errors in opening the file.
If things are working properly when you view copy.pgm with a suitable image viewer, e.g.,
gimp, you should see something interesting.
2 Flip Image (15 marks)
1. Template: flipper.asm
2. Read the data in test1.txt into the specified buffer.
3. The data read into the buffer should now be converted to consecutive integers and then stored
in a 2D array of length 24 × 7, i.e., one that has 24 columns and 7 rows. However that 2D
array will actually be represented as a 1D array*. Finally, take care to convert the entries in
the buffer (which are in ASCII) to their numerical values in base 10.
4. Write a procedure named flip.
5. Argument structure outlined in template.
* Normally, in a language like Java, we would simply specify the respective array positions of
i and j. That is, we would let i represent the row we are currently at, and j represent the column
we are currently at. In MIPS, however, our 2D array is stored as values in a 1D array. It is clear
to see that for any position [i,j] in our 2D array, we can retrieve this position by simple computing
2
( i * width ) + j. Since i represents rows, whenever we add a width (for this assignment, width is
24) we are essentially going to the next row in our conceptual 2D array. j simply represents which
column we are currently looking at.
3 Transpose Image (15 marks)
1. The template for this question is provided in transpose.asm.
2. Read the data in test1.txt into the specified buffer.
3. The data read into the buffer should now be converted to consecutive integers and then stored
in a 2D array of length 24 × 7, i.e., one that has 24 columns and 7 rows. However that 2D
array will actually be represented as a 1D array*. Finally, take care to convert the entries in
the buffer (which are in ASCII) to their numerical values in base 10.
4. Write a procedure named transpose. This routine will take your image buffer, and apply the
matrix operation transpose to it (where position (i,j) in a matrix is now at position (j,i).
5. The content of the output 2D array should then be written into a file named transposed.pgm.
6. The header will be changed! update your writefile routine to work accordingly.
(a) THIS CAN ONLY BE VIEWED if you have properly implemented (a). This means
that you are expected to write the information as you did in 1(b) and THEN write the
completed output 2D array to transposed.pgm.
(b) TESTING: You can assume that all .txt files we may use for this question use the same
header as specified in b).
4 Crop Image (30 marks)
1. Template: cropper.asm
2. You are given x1, y1, x2, y2, and a test.txt file.
3. Read the data in test1.txt into the specified buffer.
4. Generate a new .pgm named cropped.pgm that contains a cropped version of the image information contained in test.txt, i.e., reading it into an array and then cropping the rectangular
portion bounded by x1, y1, x2, y2.
5. Make sure that the cropped.pgm has the correct header! Otherwise, the cropped
image won’t be displayed properly.
6. Make sure to use P2 for “plain pgm” and 15 for the max intensity (last term from the header
in part 1 b). This means the only values that change are those specifying the dimensions of
your image. Therefore, the header must not be hard coded for this question. This extension
should be added to your write function.
7. TESTING: you can expect that all test.txt files that are tested will start with the same header
as part 1, and that x1,y1,x2,y2 will be valid inputs, i.e., they will be within the bounds of
the original array.
5 Add Image Border (25 marks)
1. Template: border.asm
2. Read the data in test1.txt into the specified buffer.
3. In a routine called bord, given borderWidth (a pixel width), take your test.txt image and
produce a new borded.pgm image with a borderwidth equal to the pixels.
4. The border will be white (=15). You can assume P2 and 15 here as well.
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5. TESTING: you can expect that all test.txt files that are tested will start with the same
header as part 1.
6 Assignment Submission Instructions
1. the **edited** template files: fileio.asm ,flipper.asm, transposer.asm, cropper.asm and border.asm must contain a main function that produces the images copy.pgm, flipped.pgm, transposed.pgm, cropped.pgm and borded.pgm (as specified in the appropriate sections). Do NOT
include the images, as we will be running the code with our own .txt files.
2. Submit your solution to myCourses before the due date.
3. Highlight the FOUR template files (which you have completed) and zip them. The zipped
file should be named <studentID.zip. If my student ID is 123456789, then the zip file to
submit will be named 123456789.zip.
4. If you have special comments about your code, feel free to include a confessions.txt file in
your zip containing your specific comments. Otherwise, simply comment your code as you
normally would. Partial marks are easier to give (though no certainty that any will be given)
if we see that you understand where your code is going wrong.
5. Your code must run and assemble, even if the final solution is not quite working. Part marks
will be awarded for correct high-level control flow and use of conventions. If something is not
working, comment-out the broken parts of code and write a comment or two about what you
expect to happen, what is happening, and what the problem may be. You are expected to
follow conventions. Doing so will save you time and a headache during debugging,
so its great for everyone! If your code does not assemble you will receive 0 points for that
question.
penalties will be given if the grader is required to change more than just the input values
(This means your main method must run, producing whatever it can produce, without having
to rewrite the main function.)
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