cv-combinators- Functional Combinators for Computer Vision

Copyright(c) Noam Lewis 2010
MaintainerNoam Lewis <>
Portabilitytested on GHC only
Safe HaskellNone



ImageProcessors is a functional (Processor-based) interface to computer vision using OpenCV.

The Processor interface allows the primitives in this library to take care of all the allocation / deallocation of resources and other setup/teardown requirements, and to appropriately nest them when combining primitives.

Simple example:

win = window 0        -- The number is essentially a label for the window
cam = camera 0        -- Autodetect camera
edge = canny 30 190 3 -- Edge detecting processor using canny operator

test = cam >>> edge >>> win

The last expression is a processor that captures frames from camera and displays edge-detected version in the window.



camera :: Int -> ImageSource Source

A capture device, using OpenCV's HighGui lib's cvCreateCameraCapture should work with most webcames. See OpenCV's docs for information. This processor outputs the latest image from the camera at each invocation.

window :: Int -> ImageSink Source

A window that displays images. Note: windows with the same index will be the same this ok? Response: Yes. It will display whatever images you give it.

resize :: Int -> Int -> InterpolationMethod -> ImageProcessor Source

OpenCV's cvResize

dilate :: Int -> ImageProcessor Source

OpenCV's cvDilate

canny Source


:: Int

Threshold 1

-> Int

Threshold 2

-> Int


-> ImageProcessor 

OpenCV's cvCanny

haarDetect Source


:: String

Cascade filename (OpenCV comes with several, including ones for face detection)

-> Double

scale factor

-> Int

min neighbors

-> HaarDetectFlag


-> CvSize

min size

-> IOProcessor Image [CvRect] 

Wrapper for OpenCV's cvHaarDetectObjects and the surrounding required things (mem storage, cascade loading, etc).

drawRects :: IOProcessor (Image, [CvRect]) Image Source

OpenCV's cvRectangle, currently without width, color or line type control

runTill :: IOProcessor () b -> (b -> IO Bool) -> IO b Source

Runs the processor until a predicate is true, for predicates, and processors that take () as input (such as chains that start with a camera).

runTillKeyPressed :: Show a => IOProcessor () a -> IO () Source

Name (and type) says it all.

keyPressed :: Show a => a -> IO Bool Source

Some general utility functions for use with Processors and OpenCV

Predicate for pressed keys