Laboratory: Collage

a. Open an existing image, such as our kitten image.

> (define source (image-show (image-load "/home/rebelsky/Desktop/kitten.jpg")))

b. Open a new 300x200 image for our collage.

> (define collage (image-show (image-new 300 200)))

c. Copy a 75x50 portion of the original image.

> (image-select-rectangle! source REPLACE ___ ___ 75 50)
> (gimp-edit-copy-visible source)

d. Paste the copied portion to elsewhere in the collage.

> (image-select-rectangle! collage REPLACE 150 50 75 50)
> (gimp-edit-paste (image-get-layer collage) 1)
> (image-select-nothing! collage)
> (gimp-image-flatten collage)

e. Paste the copied portion into four other locations in the collage. (You can choose the locations.)

As you likely noted, you did almost the exact same thing five times in the previous code. That is, you selected a rectangle in the collage, you called gimp-image-paste, you selected nothing, and you flattened the result.

Write a procedure, (my-paste! image left top width height), that encapsulates those steps.

Check your code with the following.

(define kitten (image-show (image-load "/home/rebelsky/Desktop/kitten.jpg")))
(define collage (image-show (image-new 300 200)))
(image-select-rectangle! kitten REPLACE 170 110 100 100)
(gimp-edit-copy-visible kitten)
(my-paste! collage 0 0 100 100)
(my-paste! collage 100 0 100 100)
(my-paste! collage 200 0 100 100)
(my-paste! collage 0 100 100 100)
(my-paste! collage 100 100 100 100) 

a. Open an existing image, such as our kitten image.

> (define source (image-show (image-load "/home/rebelsky/Desktop/kitten.jpg")))

b. Open a new 300x200 image for our collage.

> (define collage (image-show (image-new 300 200)))

c. Copy a 75x50 portion of the original image.

> (image-select-rectangle! source REPLACE ___ ___ 75 50)
> (gimp-edit-copy-visible source)

d. Paste the copied portion at a scale appropriate for the whole collage.

> (image-select-rectangle! collage REPLACE 0 0 300 200)
> (define pasted (car (gimp-edit-paste (image-get-layer collage) 1))
> (image-select-nothing! collage)
> (gimp-layer-scale pasted 300 200 1)
> (gimp-image-flatten collage)

Consider the following procedure.

(define p-and-s!
  (lambda (image left top width height)
    (image-select-rectangle! image REPLACE left top width height)
    (let ([pasted (car (gimp-edit-paste (image-get-layer image) 1))])
      (image-select-nothing! image)
      (gimp-layer-scale pasted width height 1)
      (gimp-image-flatten image)
      image)))

a. What does this procdure do?

b. Why do we use a let in the middle of the procedure?

c. How could we achieve the same result without using let?

d. Use this procedure to add a few more scaled versions of your copied selection to our collage.

Consider the following procedure.

(define self!
  (lambda (image)  
    (let ([width (image-width image)]
          [height (image-height image)])
      (image-select-rectangle! image REPLACE 0 0 width height)
      (gimp-edit-copy-visible image)
      (p-and-s! image 
                (* 1/10 width) (* 1/10 height)
                (* 9/10 width) (* 8/10 height)))))

a. What does this procedure do?

b. What image do you expect to result from the following?

> (define kitten (image-show (image-load "/home/rebelsky/Desktop/kitten.jpg")))
> (self! kitten)

c. Check your answer experimentally.

d. What do you expect to happen if we call self! again on the same image?

> (self! kitten)

e. Check your answer experimentally.

Write a procedure, (my-paste-scale-and-rotate! image angle left top width height) that pastes the copy region into the selected area and then rotates by the given angle. You will likely base this procedure on the p-and-s! from an earlier problem.

Here's a typical call to rotate a pasted selection.

(gimp-item-transform-rotate pasted angle 1 0 0)

In the reading and in the rotation problems above, we used 1 0 0 as the last three paramaeters to gimp-item-transform-rotate. By reading the documentation and by playing with different values, see what other rotation effects you can achieve. (Hint: Use 0 x y with different values of x and y.)

We've explored how to scale and rotate copied portions of an image. But there are many other transformations available. Search for gimp-item-transform in the Procedure Browser and see what other interesting things we can do.

Write a procedure, (andy image), that creates a new image that is the same size as image and contains four identical (but smaller) copies of image in a 2x2 grid.

You can transform only part of an image by using the image-select-rectangle! and image-transform! procedures. For example,

> (define kitten (image-show (image-load "/home/rebelsky/Desktop/kitten.jpg")))
> (define half-width (* 1/2 (image-width kitten)))
> (define half-height (* 1/2 (image-height kitten)))
> (define irgb-only-blue (section irgb-subtract <> (irgb 255 255 0)))
> (image-select-rectangle! kitten REPLACE half-width 0 half-width half-height)
> (image-transform! kitten irgb-only-blue)
> (image-select-nothing! kitten)

Using a technique like this, make a more sophisticated drella procedure that acts like andy, but recolors each of the copies.