Haskell Bindings

Haskell bindings for FlatCV are available on Hackage as the flatcv package.

Installation

Using cabal:

cabal install flatcv

Using stack:

stack install flatcv

Usage

import FlatCV
import qualified Data.Vector.Storable as V

main :: IO ()
main = do
  -- Assuming you have RGBA image data as a Vector Word8
  let
    width = 640
    height = 480
    -- imageData :: V.Vector Word8

  -- Convert to grayscale
  grayData <- grayscale width height imageData

  -- Apply Gaussian blur
  blurredData <- gaussianBlur width height 2.0 imageData

  -- Detect edges
  edges <- sobelEdgeDetection width height 4 imageData

  -- Extract a document from a photo
  (outW, outH, docData) <- extractDocumentAuto width height imageData

The bindings use Data.Vector.Storable for efficient memory handling with automatic memory management via foreign pointers.

Available Functions

Color Conversion

grayscale - Convert RGBA to grayscale (4-channel output)
grayscaleStretch - Grayscale with contrast stretching
rgbaToGrayscale - Convert to single-channel grayscale
singleToMultichannel - Convert grayscale to RGBA

Thresholding

otsuThreshold - Otsu's automatic thresholding
bwSmart - Smart black & white conversion
applyGlobalThreshold - Apply fixed threshold

Edge Detection

sobelEdgeDetection - Sobel edge detection
foerstnerCorner - Foerstner corner detection

Morphological Operations

binaryDilationDisk - Binary dilation
binaryErosionDisk - Binary erosion
binaryClosingDisk - Binary closing
binaryOpeningDisk - Binary opening

Geometric Transforms

flipX, flipY - Flip horizontally/vertically
transpose, transverse - Transpose operations
rotate90CW, rotate180, rotate270CW - Rotations
resize - Resize with bilinear interpolation

Cropping & Trimming

crop - Crop rectangular region
trim - Auto-trim borders
trimThreshold - Trim with threshold tolerance

Perspective Transform

calculatePerspectiveTransform - Calculate transform matrix
applyMatrix3x3 - Apply 3x3 transformation
detectCorners - Detect document corners

Document Extraction

extractDocument - Extract with fixed output size
extractDocumentAuto - Extract with automatic sizing

Drawing

drawCircle - Draw circle outline
drawDisk - Draw filled circle
addBorder - Add border around image

Analysis

generateHistogram - Generate histogram visualization

Segmentation

watershedSegmentation - Watershed segmentation

Utility

getExifOrientation - Read JPEG EXIF orientation
parseHexColor - Parse hex color string
convertToBinary - Convert to binary with custom colors

Pointer-Based API

For zero-copy interop with foreign data, a pointer-based API is also available. These functions work directly with Ptr Word8 and the caller is responsible for memory management.

import FlatCV
import Foreign.Ptr (Ptr)
import Foreign.Marshal.Alloc (free)
import Data.Word (Word8)

processImage :: Ptr Word8 -> IO (Ptr Word8)
processImage inputPtr = do
  -- Output is allocated by C and must be freed by caller
  outputPtr <- grayscalePtr 640 480 inputPtr
  -- ... use outputPtr ...
  free outputPtr

Available pointer-based functions include: grayscalePtr, grayscaleStretchPtr, rgbaToGrayscalePtr, singleToMultichannelPtr, gaussianBlurPtr, otsuThresholdPtr, bwSmartPtr, flipXPtr, flipYPtr, transposePtr, rotate90CWPtr, rotate180Ptr, rotate270CWPtr, calculatePerspectiveTransformPtr, applyMatrix3x3Ptr, detectCornersPtr.

Types

The library provides several data types for working with images:

Image - An image with dimensions and pixel data
Point2D - A 2D point with x and y coordinates
Corners - Quadrilateral corners (top-left, top-right, bottom-right, bottom-left)
Matrix3x3 - A 3x3 transformation matrix

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