Pixel Magic

Pixel Magic
CPE 101: Fundamentals of Computer Science

Purpose
To implement a program that accepts command-line arguments and handles errors, as well as tie together concepts
learned throughout the course.
Description
For this project, you will write functions that transform an image in the following ways:
Adjusting colors to reveal a hidden picture
Darkening colors to produce a fading effect
Averaging neighboring colors to blur an image
Download the image files here:
http://users.csc.calpoly.edu/~dkauffma/101/pixelmagic.zip
Image File Format
The P3 (.ppm) format is a text-based format (meaning that it is readable text) that defines an image as a sequence of
pixels beginning with the top-left pixel and stored in row order (i.e. every pixel in a row is stored in left-to-right order
and before any pixel in the next row).
A file conforming to the P3 format begins with header information. The header consists of the characters P3, the integer
width of the image (in pixels), the integer height of the image, and the maximum value for a color component (we will
use 255 for this value). Immediately following the header is the color information for each pixel. A pixel's color is
represented by three integers denoting the red, green, and blue components (in that order). The following example shows
how a file would look if it contained an image initially with one blue pixel, one red pixel, and one green pixel.
 P3
 3 1
 255
 0 0 255
 255 0 0
 0 255 0
 ...
The top-left pixel is said to be at location (0, 0) and the bottom-right at location at (width - 1, height - 1).
Implementation
To ensure that only string literals are passed to the open function (presently a Casey requirement), use the following
function to get a file object for reading or writing (depending on the file name):
 def open_file(file_name):
 if file_name == "puzzle.ppm":
 return open("puzzle.ppm", "r")
 if file_name == "mouse.ppm":
 return open("mouse.ppm", "r")
 if file_name == "lights.ppm":
 return open("lights.ppm", "r")
 if file_name == "decoded.ppm":
 return open("decoded.ppm", "w")
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 if file_name == "faded.ppm":
 return open("faded.ppm", "w")
 if file_name == "blurred.ppm":
 return open("blurred.ppm", "w")
 raise FileNotFoundError
In the functions below, pixels refers to a list of lists of integers, in which each inner list (representing a single pixel)
contains 3 integers, one for each color value.
main()
The main function (with optional helper functions) should perform the following steps:
Ensure provided command-line arguments are in correct format
Open the named file for reading and get its pixel data
Run the appropriate image processing routine, based on the user-provided mode (find, fade, or blur)
Write the resulting pixels to the appropriate file named below
find_image(pixels: List[List[int]]) - List[List[int]]
Return decoded pixels.
fade_image(pixels: List[List[int]], width: int, row: int, col: int, radius: int) - List[List[int]]
Return faded pixels.
blur_image(pixels: List[List[int]], width: int, reach: int) - List[List[int]]
Return blurred pixels.
Error and Usage Messages
Regardless of the filter mode, print one of the following error messages when its corresponding condition is true.
If either the filter mode or image path is not provided, your program must print:
Usage: python pixelmagic.py <mode <image
If the image argument is provided but cannot be opened (e.g. does not exist), your program must print (replacing
the blank with the name of the file given):
Error: Unable to Open ____
If the mode argument is not find, fade, or blur, your program must print:
Error: Invalid Mode
For all other messages to display, see the corresponding sections below.
Hidden Image
This program will get you started with the core functionality of processing a P3 image file. Your program must take a
single command-line argument that specifies the name of the input image file. It will output the decoded image to a file
named decoded.ppm. The output must be a valid P3 image file; do not forget to write the required header information to
it.
The puzzle image hides a real image behind a mess of random pixels. In reality, the image is hidden in the red
components of the pixels. Decode the image by increasing the value of the red component by multiplying it by 10
without allowing the resulting value to pass the maximum value of 255. In addition, set the green and blue components
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equal to the new red value. Shown below is the hidden image; it will be obvious once you have properly decoded the
puzzle image.
Fade
This program is a relatively minor modification of the previous program. In addition to the filter mode and file name, it
must take three additional command-line integer arguments:
1. The row (y-coordinate) position of the fade center
2. The column (x-coordinate) position of the fade center
3. The fade radius
These three arguments may be assumed to be integers. If any these arguments are not provided, an appropriate usage
message must be printed to the terminal and the program should terminate. This message is as follows:
Usage: python pixelmagic.py fade <image <row <col <radius
Your program will output the faded image to a file named faded.ppm, which must be a valid P3 image file; do not forget
to write the required header information to it.
This program will transform pixel values based on their distance from a specified point (this point may fall outside of the
image). The row and column coordinates specified on the command-line give the point and the radius is used to control
the fading.
For each pixel, compute the distance from the pixel location to the specified point. Scale (multiply) the color
components of the pixel by:
(radius - distance) / radius
Do not use a scale value below 0.2, which prevents very dark borders around the image).
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Blur
Your program must take two command-line arguments (in the following order):
1. The name of the input image file
The "neighbor reach" to use in the blurring calculation (this argument is optional and will be used to determine
which neighbor pixels to consider in the averaging calculation, as discussed below)
2.
If a second command-line argument is not present (i.e. the blur factor is not specified), then use a default value of 4.
Your program will output the blurred image to a file named blurred.ppm. The output must be a valid P3 ppm image file;
do not forget to write the required header information to it.
Your program will blur the image by computing, for each pixel, the average of nearby pixels (more precisely, the
averages over each color component of the nearby pixels). A pixel's blurred color will be determined by the colors of the
pixels within a specified "neighbor reach". The default "neighbor reach" is 4 (but this can be modified by a commandline argument as discussed previously). Thus, a pixel's blurred color will be determined by the colors of the pixels within
four pixels to the left or right and within four pixels above or below (this will form a square around the pixel). The
following diagram is meant to help illustrate.
This diagram shows how to compute the color for the pixel in the center (the red element). Its neighbors (within a reach
of 4) are all of the green elements. The pixels outside of this 9x9 square are not considered in the blurring calculation for
this pixel. To compute the color for the center pixel, average the red, green, and blue components (independently) of
every pixel in the 9x9 square (including the pixel itself; the red element in this diagram). Some pixels will not have the
full complement of neighbors (such as those on or near the edge of the image). In these cases, just average the existing
neighbors (i.e. those within the bounds of the image).
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Submission
On a CSL server with pixelmagic.py and pmtests.py in your current directory:
/home/dkauffma/casey.exe 101 pixelmagic
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