CS 2010 Homework 4 FAQ

Red and green crayons make brown, not yellow, right?

Yes, but red and green light make yellow light.

If you go to the color-selection dialog of any paint program, it will give you a place to try specific red-green-blue combinations to see how they look.

DrScheme has a color dialog, too. Select Preferences from DrScheme's Edit menu (or the DrScheme menu under Mac OS X), then go to the Check Syntax panel and click one of the Change Color buttons.

I can't convert an image to a list of colors. DrScheme says that the function color-list is not defined.

The name of the function is image->color-list. The arrow (really a dash followed by a greater-than sign) is part of the name.

I can't figure out how to start exercise 4.5.

More hints: The contract for negate-colors should be list-of-color -> list-of-color. The photo-negative function merely converts the image to a list of colors, calls negate-colors, and converts the result back to an image.

I still can't figure out how to start exercise 4.5.

Write three functions:

• photo-negative: uses image->color-list, passes the resulting list to negative-colors, and finally passes the resulting negated list to color-list->image to get the final result.
• negative-colors: a list-of-color -> list-of-color that follows simply from the list-of-color template.
• negative-color: a color -> color function that is called by negative-colors.