Copyright	(c) 2022 Mirko Westermeier
License	MIT
Safe Haskell	Safe-Inferred
Language	Haskell2010

RGB

Contents

The RGB color type
Utilty functions
Images
Codewars greyscale conversion
- Greyscale images

Description

RGB color handling library

Synopsis

data RGB a = RGB {
- red :: a
- green :: a
- blue :: a
}
toList :: RGB a -> [a]
fromList :: [a] -> Maybe (RGB a)
showHex :: PrintfArg a => RGB a -> String
parseRGB :: String -> Maybe (RGB Int)
type Image = [[RGB Int]]
type ImageList = [[[Int]]]
toImageList :: Image -> ImageList
fromImageList :: ImageList -> Maybe Image
greyScale :: RGB Int -> RGB Int
color2grey :: Image -> Image
color2grey' :: ImageList -> Maybe ImageList

The RGB color type

data RGB a #

A triple type representing the three color components of RGB color values. Since most systems expect component values from 0 to 255, unsigned integer types like RGB Word or RGB Int are most useful for color values. But keeping it parameterized here allows for a useful Applicative instance (see below).

Constructors

RGB
Fields red :: a Red color value green :: a Green color value blue :: a Blue color value

Instances

Instances details

Functor RGB #	Application of a given function to all color components: fmap (*2) (RGB 2 7 21) == RGB 4 14 42
Instance details Defined in RGB Methods fmap :: (a -> b) -> RGB a -> RGB b # (<$) :: a -> RGB b -> RGB a #
Applicative RGB #	The `Applicative` instance of `RGB` can act as a component-wise application: (RGB (+5) (`div` 2) (6) <> RGB 12 74 7) == RGB 17 37 42
Instance details Defined in RGB Methods pure :: a -> RGB a # (<>) :: RGB (a -> b) -> RGB a -> RGB b # liftA2 :: (a -> b -> c) -> RGB a -> RGB b -> RGB c # (>) :: RGB a -> RGB b -> RGB b # (<*) :: RGB a -> RGB b -> RGB a #
Eq a => Eq (RGB a) #	Default `Eq` instance. Two `RGB` values are equal iff all components `red`, `green`, `blue` are equal.
Instance details Defined in RGB Methods (==) :: RGB a -> RGB a -> Bool # (/=) :: RGB a -> RGB a -> Bool #
Show a => Show (RGB a) #	Default `Show` instance. Example: `"RGB {red = 17, green = 37, blue = 42}"`. See `showHex` for a compressed hexadecimal stringification.
Instance details Defined in RGB Methods showsPrec :: Int -> RGB a -> ShowS # show :: RGB a -> String # showList :: [RGB a] -> ShowS #

Utilty functions

toList :: RGB a -> [a] #

Creates a three element list of RGB color components:

toList (RGB 17 37 42)  ==  [17, 37, 42]

fromList :: [a] -> Maybe (RGB a) #

Tries to create a color from a list of values, assuming exactly three values:

fromJust (fromList [17, 37, 42])  ==  RGB 17 37 42

showHex :: PrintfArg a => RGB a -> String #

Hexadecimal color representation for printfable components. For values between 0 and 255 it is the inverse of parseRGB (modulo Maybe):

showHex (fromJust $ parseRGB $ "#11252a")  ==  "#11252a"

parseRGB :: String -> Maybe (RGB Int) #

Parse RGB Int values from hexadecimal strings like #aabbcc.

fromJust (parseRGB $ showHex $ RGB 17 37 42)  ==  RGB 17 37 42

Images

type Image = [[RGB Int]] #

Super-simple image representation as a two-dimensional list of pixels of type RGB a.

type ImageList = [[[Int]]] #

Super-oversimplified image representation as a three-dimensional list of color components of type Int.

toImageList :: Image -> ImageList #

Creates an ImageList from an Image.

fromImageList :: ImageList -> Maybe Image #

Tries to create an Image from an ImageList using fromList.

Codewars greyscale conversion

greyScale :: RGB Int -> RGB Int #

Simple greyscale conversion of a RGB Int color according to the Codewars kata Convert Color image to greyscale:

greyScale (RGB r g b)  ==  RGB ((r+g+b)/3) ((r+g+b)/3) ((r+g+b)/3)

but using Fractional arithmetics.

Greyscale images

color2grey :: Image -> Image #

Application of greyScale to each RGB Int pixel of an Image

color2grey' :: ImageList -> Maybe ImageList #

Application of greyScale to each RGB Int pixel of an ImageList