Lab: Transforming images

Assigned

Friday, 20 September 2024

Summary

We explore techniques for transforming images, focusing on the use of anonymous procedures.

Procedures to remember

Basic color procedures

• (rgb r g b) - create a new RGB color.
• (rgb r g b a) - create a new RGB color, also specifying the alpha channel.
• (rgb-red c) - extract the red component of an rgb color.
• (rgb-green c) - extract the green component of an rgb color.
• (rgb-blue c) - extract the blue component of an rgb color.

Transforming colors

• (rgb-darker c) - create a darker version of c (if possible).
• (rgb-ligheter c) - create a lighter version of c (if possible).
• (rgb-redder c) - create a redder version of c (if possible).
• (rgb-greener c) - create a greener version of c (if possible).
• (rgb-bluer c) - create a bluer version of c (if possible).
• (rgb-pseudo-complement c) - get the pseudo-complement of c.
• (rgb-complement c) - get the HSV complement of c.
• (rgb-greyscale c) - convert c to greysacle.
• (rgb-phaseshift c) - phase shift each component of c by 128, adding 128 to values less than 128 and subtracting 128 from values greater than or equal to 128.
• (rgb-rotate-components c) - rotate the RGB components of c.

Combining colors

• (rgb-add c1 c2) - Add the components of two RGB colors.
• (rgb-subtract c1 c2) - Subtract corresponding components of c2 from c1.
• (rgb-average c1 c2) - Average the components in c1 and c2.

Working with color names

• (all-color-names) - list all the color names.
• (color-name->rgb name) - convert a color name to an RGB color.
• (find-colors name) - find all the colors that include name.

Working with images

• (with-image-file fn) - loads an image, calling fn with the image as input.
• (with-image-from-url url fn) - loads an image from url, calling fn on the image as input.
• (pixel-map color-transformation image) - apply a color transformation to each pixel in an image.
• `(image-save img filename) - save an image to a file.

Working with procedures

• (section (expression-with-underscores)) - Build a new procedure that takes one parameter for each underscore in expression-with-underscores.
• (o fun1 fun2 fun3 ... funk) - Build a new procedure that applies funk then … then fun3 then fun2 then fun1 to its parameter.

The lab

• Use the file transforming-images.scm.
• Find an image you like, such as your campus directory picture (or President Harris’ directory picture, or your instructor’s directory picture) and save it to your desktop.

Acknowledgements

The kitten image was downloaded from http://public-photo.net/displayimage-2485.html. Unfortunately, the site behind that URL has disappeared. Nonetheless, the kitten image lives on.

This lab was originally written in 2024Sp, based on a lab from 2017Sp.