Foreground Modeling

Detect foreground movement in video frames by looking for changes relative to a static background. More...

Typedefs
typedef struct roc_foreground_type *	roc_foreground
	Handle to a private foreground modeling type.

Functions
roc_error	roc_new_foreground (roc_foreground *foreground)
	Initialize a new foreground model. More...
roc_error	roc_foreground_add_frame (roc_foreground foreground, const roc_image frame, roc_image *mask)
	Classify image pixels into foreground and background. More...
roc_error	roc_foreground_quality (const roc_image mask, float *foreground_quality)
	Calculate a quality value based on the number of foreground pixels in the image. More...
roc_error	roc_foreground_roi (const roc_image mask, size_t *x, size_t *y, size_t *width, size_t *height)
	Identify a rectangular region of interest that captures the foreground content. More...
roc_error	roc_foreground_render (const roc_image frame, const roc_image mask, roc_image *rendering)
	Construct an image that visualizes the foreground. More...
roc_error	roc_free_foreground (roc_foreground *foreground)
	Free a foreground model. More...

Detailed Description

Detect foreground movement in video frames by looking for changes relative to a static background.

Function Documentation

roc_new_foreground()

roc_error roc_new_foreground

(

roc_foreground *

foreground

)

Initialize a new foreground model.

Add images to the model with roc_foreground_add_frame.

Example

roc_foreground foreground;
roc_new_foreground(&foreground);

Parameters

[out]

foreground

Foreground model to initialize.

Remarks

This function is reentrant.

See also

roc_free_foreground

roc_foreground_add_frame()

roc_error roc_foreground_add_frame	(	roc_foreground	foreground,
		const roc_image	frame,
		roc_image *	mask
	)

Classify image pixels into foreground and background.

The output mask is a ROC_GRAY8 image the same size as the input frames. Values in mask are either zero to indicate background, or 255 to indicate foreground. The mask can be passed to roc_foreground_quality or roc_foreground_roi. Free mask after use with roc_free_image.

For a visual understanding of the algorithm see roc_foreground_render.

Example

roc_foreground foreground = ...;
roc_image frame = ...;
roc_image mask;
roc_model_foreground(foreground, frame, &mask);

Parameters

[in,out]	foreground	Background model to update.
[in]	frame	Image to model.
[out]	mask	ROC_GRAY8 foreground/foreground mask.

Remarks

This function is thread-safe.

See also

roc_foreground_quality roc_foreground_roi

roc_foreground_quality()

roc_error roc_foreground_quality	(	const roc_image	mask,
		float *	foreground_quality
	)

Calculate a quality value based on the number of foreground pixels in the image.

foreground_quality = (number of pixels in mask) ^ 2 / (number pixels in motion region * number pixels in image)

Parameters

[in]	mask	Input foreground mask from roc_foreground_add_frame.
[out]	foreground_quality	Quality value based on the number of foreground pixels in the image.

Remarks

This function is thread-safe.

See also

roc_foreground_add_frame.

roc_foreground_roi()

roc_error roc_foreground_roi	(	const roc_image	mask,
		size_t *	x,
		size_t *	y,
		size_t *	width,
		size_t *	height
	)

Identify a rectangular region of interest that captures the foreground content.

Parameters

[in]	mask	Input foreground mask from roc_foreground_add_frame.
[out]	x	Output region of interest rectangle, top-left corner horizontal position.
[out]	y	Output region of interest rectangle, top-left corner vertical position.
[out]	width	Output region of interest rectangle width.
[out]	height	Output region of interest rectangle height.

Remarks

This function is thread-safe.

See also

roc_foreground_add_frame

roc_foreground_render()

roc_error roc_foreground_render	(	const roc_image	frame,
		const roc_image	mask,
		roc_image *	rendering
	)

Construct an image that visualizes the foreground.

Free rendering

Parameters

[in]	frame	Input frame from roc_foreground_add_frame.
[in]	mask	Resulting mask from roc_foreground_add_frame.
[out]	rendering	Rendered image the same size as frame.

Remarks

This function is thread-safe.

roc_free_foreground()

roc_error roc_free_foreground

(

roc_foreground *

foreground

)

Free a foreground model.

Deallocate memory for foreground previously allocated with roc_new_foreground.

Example

roc_foreground foreground = ...;
roc_free_foreground(foreground);

Parameters

[in]

foreground

Background to free.

Remarks

This function is reentrant.

See also

roc_new_foreground