Video::Capture::V4l::Imager 0.01

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Video::Capture::V4l::Imager 0.01
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NAME
Video::Capture::V4l::Imager - Capture images from a video webcam

SYNOPSIS
use Video::Capture::V4l::Imager;

my $vcap = Video::Capture::V4l::Imager->new(
width => 320,
height => 240,
);

# Adjust camera brightness if necessary
$vcap->brightness(32_000);

# Capture an image, back comes an Imager object
my $img = $vcap->capture();

# Save it as JPEG
$img->write(file => 'mycapture.jpg')
or die "Can't write: $!";

DESCRIPTION
Video::Capture::V4l::Imager captures still images from a USB video cam
connected to your Linux box. The pictures come back as Imager objects
(see the Imager module on CPAN for details) and can be easily
manipulated and saved to disk.

Video::Capture::V4l::Imager is a convenience wrapper around Marc
Lehmann's Video::Capture::V4l module. It uses the following procedure to
obtain the still images from the video stream:

http://www.perlmonks.org/?node=474047

Capturing Images
To initialize V4l with your connected video camera, call the constructor
with the width and height setting according to what's supported by the
video camera:

my $vcap = Video::Capture::V4l::Imager->new(
width => 320,
height => 240,
);

Note that this call will fail if your video camera doesn't support the
specified width and height setting.

To capture a picture from the video stream, call

$vcap->capture();

which will return an Imager object on success or "undef" otherwise.

Adjusting the Camera
To adjust the brightness setting of the camera, use

$vcap->brightness(32_000);

and pass the integer value of the desired brightness setting.

To calibrate the camera to obtain an image that has a given average
brightness, use "calibrate":

my $vcap = Video::Capture::V4l::Imager->new(
width => 320,
height => 240,
avg_optimal => 128,
avg_tolerance => 20,
brightness_min => 0,
brightness_max => 65535,
calibration_tries => 5,
);

$vcap->calibrate();

This will start a simple binary search by taking a picture, checking its
average brightness via "img_avg()" (see below) and adjusting the camera
brightness to get to a desired optimal brightness "avg_optimal". within
a selectable tolerance "avg_tolerance".

"calibrate()" returns the best camera brightness setting found.

The minimum and maximum settings for camera brightness (which depend on
the camera used) are set in "brightness_min" and "brightness_max".

The maximum number of test exposures is set in "calibration_tries",
after this number is reached, the camera brightness that worked best so
far gets returned.

Utility functions
The following utility methods for Imager objects have been included in
this module:

"$i->img_avg()"
Calculates the average brightness of an image by adding up all
channels of every pixel and then dividing it by 3 times the number
of pixels. Handy to get a feel if an image is over- or underexposed,
by a very crude measure.

"$i-">img_changed($other_img, $diff)>
Checks if two images are significantly different, used to tell if
two consecutive still images taken from a video stream show that
something's going on in the scene.

Calculates the difference in channel values of all pixels and
compares it to the number passed in $diff. If the sum of all channel
differences is greater than $diff, "img_changed" returns true and
false otherwise.

Note that the counter will be increased by up to 3 points per pixel
(red, green, blue channels), so factor that into $diff.

NOTES
Note that this module contains inline C code and will take significantly
longer to start up on the first run. It will speed up significantly on
consecutive runs, because the object code will be preserved once it has
been compiled.

LEGALESE
Copyright 2007 by Mike Schilli, all rights reserved. This program is
free software, you can redistribute it and/or modify it under the same
terms as Perl itself.

AUTHOR
2007, Mike Schilli <[email protected]>