Laboratory: Transforming Images

a. Find an image you like, such as your campus directory picture (or President Kington's directory picture), and save it to your desktop.

b. Using image-load, image-show, and anything else that you think will be useful, load and show that image. Note that the path to the file is likely to be something like "/home/username/Desktop/image.jpg", although you will need to replace the user name and image.

c. Name the loaded image pic.

d. Using image-load, image-show, and anything else you think will be useful, load and show "/home/rebelsky/glimmer/samples/rebelsky-pic.jpg". Name the loaded image prof.

e. Using image-variant, make prof a bit bluer.

f. Using image-save, save the modified image to your desktop.

g. Try opening the modified image by double-clicking on it.

h. You probably don't need the modified image any more. Delete it.

As you may recall, the o operator composes multiple procedures , creating a new procedure that applies each in sequence to the result of the previous one.

Consider the following definition.

> (define irgb-modify2 (o irgb-redder irgb-redder irgb-bluer irgb-bluer))

a. What RGB components do you expect to get if you apply irgb-modify2 to (irgb 127 127 127)?

b. Check your answer experimentally by entering the following expression.

> (irgb->string (irgb-modify2 (irgb 127 127 127)))

c. What effect do you expect to get if you apply irgb-modify2 to the image you obtained in exercise 1?

d. Check your answer experimentally.

Predict the effects of each of the following compound transformations, and then try them on a few sample colors and your image.

a. (o irgb-rotate irgb-rotate irgb-rotate)

b. (o irgb-lighter irgb-lighter irgb-lighter irgb-darker irgb-darker irgb-darker)

c. (o irgb-rotate irgb-rotate irgb-bluer irgb-rotate)

d. An “interesting” compound transformation that you design yourself.

As you may recall from the reading, the section operation creates a new procedure from an existing procedure by filling in one or more parameters. In the reading, we considered section from the perspective of colors. For this lab, we'll first explore it with numeric operations.

Consider the following definitions.

(define add10 (section + 10 <>))
(define add11 (section + <> 11))
(define sub5 (section - 5 <>))
(define sub6 (section - <> 6))
(define mod7a (section mod <> 7))
(define mod7b (section mod 7 <>))

a. What value do you expect to get if you apply each of these procedures to the value 12? What about the value 5?

b. Check your answer experimentally.

> (add10 12)
___
> (add11 12)
___
> (sub5 12)
___
> (sub6 12)
___
> (mod7a 12)
___
> (mod7b 12)
___
> (add10 5)
___
> (add11 5)
___
> (sub5 5)
___
> (sub6 5)
___
> (mod7a 5)
___
> (mod7b 5)
___

c. What do your results suggest about the behavior of section?

Consider the following definition.

(define proc (o (section * 5 <>) (section - <> 2)))

a. What values do you expect to get when you apply proc to the inputs 1, 2, 3, 4, and 5?

b. Check your answer experimentally.

We've just used the section procedure to build arithmetic operations. But we can certainly use it to build color transformations from the binary color operations. Consider the following definitions.

(define irgb-modify-6a (section irgb-add (irgb 64 0 64) <>))
(define irgb-modify-6b (section irgb-average (irgb 64 0 64) <>))
(define irgb-modify-6c (section irgb-subtract (irgb 64 0 64) <>))
(define irgb-modify-6d (section irgb-subtract <> (irgb 64 0 64)))

a. What effect do you expect each of these procedures to have on the color (irgb 127 127 127)?

b. Check your answer experimentally.

c. What effect do you expect each of these procedures to have on your sample image?

d. Check your answer experimentally.

a. Suppose we did not have irgb-redder. How would you define it in terms of irgb-add, irgb-subtract, and/or irgb-average? (Yes, you can also use compose and o.)

b. Suppose we did not have irgb-complement. How would you define it in terms of irgb-add, irgb-subtract, and/or irgb-average? (Yes, you can also use compose and o.)

c. Suppose we did not have irgb-darker. How would you define it in terms of irgb-add, irgb-subtract, and/or irgb-average? (Yes, you can also use compose and o.)

Consider the following definitions.

(define k (image-load "/home/rebelsky/Desktop/kitten.jpg"))
(define proc8a (section image-variant <> irgb-complement))
(define proc8b (section image-variant k <>))

a. proc8a is a unary procedure. What type of parameter does proc8a expect? That is, does it expect a color, a string, an image, a color transformation, a number, or something else?

b. proc8b is a unary procedure. What type of parameter does proc8b expect? That is, does it expect a color, a string, an image, a color transformation, a number, or something else?

c. Give a sample call to proc8a.

d. Give a sample call to proc8b.

e. What does proc8a do? Come up with a better name for it.

f. What does proc8b do? Come up with a better name for it.

While we only have a few basic transformations, there are, in some sense, an infinite number of ways to combine them. Try to find an interesting composition of basic transformations that someone might want to use as a filter.

As you have undoubtedly noticed, RGB colors are represented as integers. That means that we can transform colors with arithmetic operations as well as with component based operations. What do you think the following operations will do to your image? Try some of them to find out. Then, try a few of your own devising.

> (define t1 (section * 2 <>))
> (define t2 (section * 3 <>))
> (define t3 (section * 1.5 <>))
> (define t4 (section * 256 <>))
> (define t5 (section - <> (irgb 0 0 255)))

Make sure you save your work regularly. Some of these procedures have the potential to crash the GIMP or MediaScript.

Try developing your own interesting RGB transformation procedures and applying them to picture.