Colors in Context

Due: 11 a.m., Wednesday, 8 October 2008

Summary: Build a set of tools to let you visualize a set of color color schemes based on a transformation and a list of colors.

Purposes: To practice using list iteration, anonymous procedures, and color transformations. To gain experience implementing procedures as described in formal documentation.

Expected Time: Two to three hours.

Collaboration: We encourage you to work in groups of size three. You may, however, work alone or work in a group of size two or size four. You may discuss this assignment with anyone, provided you credit such discussions when you submit the assignment.

Submitting: Email your answer to . The title of your email should have the form HW5 and should contain your answers to all parts of the assignment. Scheme code should be in the body of the message.

Warning: So that this assignment is a learning experience for everyone, we may spend class time publicly critiquing your work.

Background

In his first guest lecture, Professor Kluber gave us some terminology for describing relationships between colors: A color scheme can be complementary, analogous, monochromatic, or discordant. Professor Kluber also encouraged us to think about how colors can look different depending on the context in which they appear.

Do we know how to compute complements, analogs, and other variants of a color? We know some ways. In particular, we can use the basic color transformations that were discussed in the reading on transforming RGB colors. For example, to compute the pseudo-complement of a color, subject, we might use (rgb-complement subject).

In this assignment, you will use these color transformations, along with list iteration techniques and the drawings-as-values representation, to produce visualizations of colors in context.

Assignment

1. Write the procedure described by the following documentation. A couple of notes:

  • A "unary procedure" is a procedure that has exactly one parameter.
  • The value produced by the procedure should be a drawing object, as in the “drawings as values” representation of images. 
;;; Procedure:
;;;   color-in-context-drawing
;;; Parameters:
;;;   subject, an RGB color
;;;   transform, a unary procedure 
;;; Purpose:
;;;   To create a drawing where the foreground is the subject color
;;;     and the background is the result of applying the given transformation 
;;;     to subject.
;;; Produces:
;;;   drawing, a drawing object
;;; Preconditions:
;;;   transform takes an RGB color as its only parameter and produces
;;;     an RGB color as its result.
;;; Postconditions:
;;;   drawing consists of a 50x50 square of color subject centered
;;;     in front of a 100x100 square of the color resulting from applying
;;;     transform to subject.
;;;   The upper left hand corner of the larger square has coordinates 0,0.

2. Suppose that primary-colors is defined as follows. 

  (define primary-colors (map cname->rgb (list "red" "blue" "green")))
  1. What does the following expression do? 
          (map (lambda (color) (color-in-context-drawing color rgb-complement))
           primary-colors)
  2. What does the following expression do? Why did we use foreach! instead of map? 
          (foreach! (lambda (color) (image-show 
                                  (drawing->image
    			            (color-in-context-drawing color rgb-complement) 100 100)))
                primary-colors)

3. Write the procedure described by the following documentation. You will need to use map or foreach! procedure, along with the color-in-context procedure you defined above. 

;;; Procedure:
;;;   show-colors-in-context
;;; Parameters:
;;;   subjects, a list of RGB colors
;;;   transform, a unary procedure 
;;; Purpose:
;;;   To show each color in subjects in the context of the result 
;;;     of applying the given transformation to the color.
;;; Produces:
;;;   Nothing. Called for its side-effects.
;;; Preconditions:
;;;   transform takes an RGB color as a parameter and produces
;;;     an RGB color as its result.
;;; Postconditions:
;;;   For each color in subjects, GIMP shows a 100x100 image showing
;;;     a square of that color centered on a background of the color
;;;     that results from applying transform to the original color.

4. We can transform colors in a number of ways to generate interesting color schemes. Several possible transformations are described below.

Define color-list to be a list of at least five RGB colors of your choice. Then, write expressions using show-colors-in-context procedure to show the colors in your list with the transformations described below.

Note: You will create lots of images in the process of doing this problem. Remember that you can ask GIMP to close all of its images at once using the File/Close All menu item.

  1. Complementary. The background color is the pseudo-complement of the foreground color.
  2. Monochromatic: Darker. The background color is a darker shade of the foreground color.
  3. Monochromatic: Lighter. The background color is a lighter shade of the foreground color.
  4. Monochromatic: Black. The background color is black, regardless of the foreground color.
  5. Monochromatic: White. The background color is white, regardless of the foreground color.
  6. Pseudo-analogous: Redder. The background color is slightly redder than the foreground color. (It is up to you how much redder.)
  7. Pseudo-analogous: Greener. The background color is slightly greener than the foreground color.
  8. Pseudo-analogous: Bluer. The background color is slightly bluer than the foreground color.
  9. Discordant. The background color is neither complementary to, nor analogous to, nor a monochromatic variant of the foreground color. It's up to you do decide how to combine transformations to produce such a color.

Postscript

After completing the last problem, you may be thinking to yourself, “Isn't there an easier way to do this? What if I could write a procedure to apply lots of transformations to just a single color?” This is possible, but you don't have the tools to do it just yet. You'll see this idea in a later problem.

Important Evaluation Criteria

We will evaluate your work based on the correctness and readability of your code. Code that is exceptionally elegant, insightful, or well-crafted may earn a plus.

Extra credit opportunity

Observe that map can take any number of lists as its parameters. For example, 

> (map + (list 1 2 3) (list 10 20 30))
(11 22 33)

Use this idea, along with drawing-hshift, to write a new version of show-colors-in-context that shows all of the subject/context color squares side-by-side in a single image, rather than each color square in a separate image.

Jerod Weinman