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https://github.com/btsimonh/node-red-contrib-ocv

Node Red node set for using node-opencv in Node Red
https://github.com/btsimonh/node-red-contrib-ocv

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Node Red node set for using node-opencv in Node Red

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# node-red-contrib-ocv

Node Red node set for using node-opencv in Node Red



# nodes



## ocv global



This node adds a structure 'ocv-api' to the globals in NodeRed, allowing function nodes to use node-opencv functionality, but simplify interaction with the node-red-contrib-ocv node set.



The api may be accessed like:



var ocvapi = global.get("ocv-api");



and contains:



```

{

   cv: node-opencv root object,

   getimagename( obj, msg ): return the input image name or null, may set status and produce warnings\n"+

   releaseone( msg, name ): release the named img/data from the frame in the msg\n"+

   releaseall( msg ): release all images/data in the frame in the msg\n"+

   sendframe( obj, data, msg ): send a NEW msg containing the original frame from msg plus the data named as obj.name\n"+

}

```



See API notes below.



## ocv videoin



reads video from a camera



## ocv resize



Resizes an image



## ocv encode



Encodes an image to jpeg data in a buffer



## ocv bg



calculates the difference between an image and a running average background using MOG2 from Opencv



## ocv order



queues messages and emits them in frame order.



Note: currently this will be fragile if a frame is lost (no protection against too many frames being stored).



## ocv contours



extracts contours from an image synchronously using



> var cnts = im.findContours(node.api.cv.RETR_EXTERNAL, node.api.cv.CHAIN_APPROX_SIMPLE);



## ocv template



not actually a node - template.js and template.html are files to use as templates for creating a new node.



# API Notes



## frame representation



A frame of data is a collection of data for a specific point in time.



This may contain one or more opencv images, plus other data (e.g. jppeg data, contours, etc).



A frame is stored in a Node-Red message at msg.payload.frame



The base structure is ;



```

frame: {

   number: the frame number since start

   data:{ - a container for named data within the frame, e.g.:

     videoin: - opencv mat representing the frame read by the node 'videoin'

   }

}

```



Frame data is generally named according to the node name of the originating node.



When a node sends a frame, it adds it's name in msg.payload.name, and this may be used by the next node to determine which chunk of data it is to process if not configured to process a specifically named piece of data.



## node representation.



The API calls are designed for use from the native nodes.  However, they may be used from function nodes if certain expectations are met.



for getimagename( obj, msg ) and sendframe(obj, data, msg ):



'obj' in a call is normally the node itself.  The calls will use the following functions and variables:



```

obj.api - must be the api structure

obj.status - std NR function

obj.error - std NR function

obj.warn - std NR function

obj.send(msg) - std NR function

obj.toprocess - the name of the data to be processed from the frame

obj.haserrored - a flag indicating that an error has occurred since 'reset'.

obj.reset(obj) - an optional function indicating a msg received was a rest message.

```



### getimagename( obj, msg )



This function takes the 'obj' and an input msg, and retrieves the name of the data to process.



It first checks for a rest msg, and then checks other msg parameters are correct for an ovc message containing a frame.



If there is any problem, an error will be show using status, and obj.error() will be called; but only for the first error encountered.



If there is any problem, the function will return null, which indicates there is no processing to do.



### getimage(node, msg, name)



Retrieves the named image/data.  If name is not provided, then it will use getimagename to get one.



By having a function for this rather than just accessing the msg directly, we allow for future enhancements.



### releaseone(obj, msg, name)



Releases the memory for the named image/data in the frame in the msg



### releaseall(obj, msg)



Releases the memory for all the images/data in the frame in the msg



### sendframe( obj, data, msg )



creates a new msg from the frame in msg, add 'data' to the frame using 'obj.name' as the name of the data, and sends the new msg on the first output.



## example code



example:



```

    node.api = global.get('ocv-api');

    node.name = 'myname';

    var im = node.api.getimage(node, msg);

    // if error or no processing required

    if (im){

       (do something with img)

       api.sendframe(node, outputdata, msg);

       if (releaseinput){

           api.releaseone(node, msg, toprocess);

       }

    }

    if (releaseall){

        api.releaseall(node, msg);

    }

```