Data.ChainCodes

Decoding of chain codes embedded in images.

Documentation

type Colour = PixelRGB8

Friendly alias for PixelRGB8

type PixelPos = (Int, Int, Int)

Position of a pixel along with the clock direction used by chainCode.

type Position = (Int, Int)

Simple alias for Int pair

readRGB8 :: FilePath -> IO (Either String (Image PixelRGB8))

Reads in an Image that uses PixelRGB8 as its base. Rejects any other format.

onImage :: (forall a. Image a -> b) -> DynamicImage -> b

Generic application over DynamicImage.

findSpot :: Image PixelRGB8 -> Colour -> Maybe Position

Given an Image parametrised by PixelRGB8 and given a Colour, we try to find the first pixel that matches the Colour.

We start checking at the top left corner of the image, checking each row fully before progressing a column: we check (width, height + 1) then (width, height + 1) and so on where top left corner of the image is (0, 0) and positive height is towards the bottom.

chainCode :: Image PixelRGB8 -> Colour -> Maybe [Position]

Given an Image parametrised by PixelRGB8 and given a Colour, we try to find the chain code in the binary image which has the passed in colour.

Note that only a single shape is accepted inside of the image. The starting positing is determined using findSpot.

The output list contains unique positions only: the beginning and end position are not treated the same. If findSpot fails, we return Nothing.