Image::Sane(3pm)

NAME
Image::Sane - Perl extension for the SANE (Scanner Access Now Easy) Project

VERSION
5

SYNOPSIS
  use Image::Sane;
  my @devices = Image::Sane->get_devices;
  my $device = Image::Sane::Device->open($devices[0]->{name});
  my $param = $device->get_parameters;
  $device->write_pnm_header($fh, $param);
  my ($data, $len) = $device->read ($param->{bytes_per_line});
  print $fh $data;

DESCRIPTION
These Perl bindings for the SANE (Scanner Access Now Easy) Project allow you to access SANE-compatible scanners in a Perlish and object-oriented way, freeing you from the casting and memory management in C, yet remaining very close in spirit to original API.

Find out more about SANE at <http://www.sane-project.org>.

SUBROUTINES/METHODS

  Image::Sane->get_version
Returns an array with the SANE_VERSION_(MAJOR|MINOR|BUILD) versions:

  join('.', Image::Sane->get_version)

  Image::Sane->get_version_scalar
Returns an scalar with the SANE_VERSION_(MAJOR|MINOR|BUILD) versions combined as per the Perl version numbering, i.e. sane 1.0.19 gives 1.000019. This allows simple version comparisons.

  Image::Sane->get_devices
This function can be used to query the list of devices that are available. If the function executes successfully, it returns a array of hash references with the devices found. The returned list is guaranteed to remain valid until (a) another call to this function is performed or (b) a call to sane_exit() is performed. This function can be called repeatedly to detect when new devices become available.

If argument local_only is true, only local devices are returned (devices directly attached to the machine that SANE is running on). If it is false, the device list includes all remote devices that are accessible to the SANE library.

  try {
      @devices = Image::Sane->get_devices;
      print "Name: $devices[0]->{name}\n";
      print "Vendor: $devices[0]->{vendor}\n";
      print "Model: $devices[0]->{model}\n";
      print "Type: $devices[0]->{type}\n";
  }
  catch {
      print "Error getting devices:", $_->error, "\n";
  };

  Image::Sane::Device->open
This function is used to establish a connection to a particular device. The name of the device to be opened is passed in argument name. If the call completes successfully, a Image::Sane::Device object is returned. As a special case, specifying a zero-length string as the device requests opening the first available device (if there is such a device).

  my $device = Image::Sane::Device->open($device_name);

  Image::Sane::Device->get_option_descriptor
This function is used to access option descriptors. The function returns a hash reference with the option descriptor for option number n of the Image::Sane::Device object. Option number 0 is guaranteed to be a valid option. Its value is an integer that specifies the number of options that are available for the Image::Sane::Device object (the count includes option 0). If n is not a valid option index, the function croaks.

  try {
      $option = $device->get_option_descriptor($n);
      print "Name: $option->{name}\n";
      print "Name: $option->{title}\n";
      print "Name: $option->{desc}\n";
      print "Name: $option->{type}\n";
      print "Name: $option->{unit}\n";
      print "Name: $option->{cap}\n";
      print "Name: $option->{max_values}\n";
      print "Name: $option->{constraint_type}\n";
  }
  catch {
      print "Error getting option descriptor:", $_->error, "\n";
  };

The contents of the hash keys "name", "title", "desc", "type", "unit", "cap" and "constraint_type" are as per the C API description (<http://www.sane-project.org/html>). There is a further constraint key that either contains an array with the possible option values, or a hash with keys "max", "min", and "quant".

The max_values key replaced the size key in the C API, and contains the maximum number of values that the option may contain.

  Image::Sane::Device->get_option
Returns the current value of the selected option.

  try {
      $value = $device->get_option($n);
      print "value: $value\n";
  }
  catch {
      print "Error getting option:", $_->error, "\n";
  };

For $option->{max_values} > 1, $value is a reference to an array.

  Image::Sane::Device->set_auto
Commands the selected device to automatically select an appropriate value. This mode remains effective until overridden by an explicit set_option request.

  $device->set_auto($n);

  Image::Sane::Device->set_option
Sets the selected option, returning flags in $info, which are described in the C API (<http://www.sane-project.org/html>).

  $orig = $device->get_option($n);
  $info = $device->set_option($n, $value);
  if ($info & SANE_INFO_INEXACT) {
   $value = $device->get_option($n);
   print "rounded value of $opt->{name} from $orig to $value\n";
  }

For $option->{max_values} > 1, $value can be a reference to an array.

  Image::Sane::Device->get_parameters
This function is used to obtain the current scan parameters. The returned parameters are guaranteed to be accurate between the time a scan has been started (Image::Sane::Device->start() has been called) and the completion of that request. Outside of that window, the returned values are best-effort estimates of what the parameters will be when Image::Sane::Device->start() gets invoked. Calling this function before a scan has actually started allows, for example, to get an estimate of how big the scanned image will be.

  try {
      $param = $device->get_parameters;
      print "format $param->{format}\n";
      print "last_frame $param->{last_frame}\n";
      print "bytes_per_line $param->{bytes_per_line}\n";
      print "pixels_per_line $param->{pixels_per_line}\n";
      print "lines $param->{lines}\n";
      print "depth $param->{depth}\n";
  }
  catch {
      print "Error getting parameters:", $_->error, "\n";
  };

Please see the C documentation (<http://www.sane-project.org/html>) for details of the above values.

  Image::Sane::Device->start
This function initiates acquisition of an image from the device specified.

  $device->start;

  Image::Sane::Device->read
This function is used to read image data from the device specified. The number of bytes returned in $buf is stored in $len. A backend must set this to zero when an error is thrown. if the call succeeds, the number of bytes returned can be anywhere in the range from 0 to $maxlen bytes.

  $param = $device->get_parameters;
  $maxlen = $param->{bytes_per_line};
  ($buf, $len) = $test->read ($maxlen);

If this function is called when no data is available, one of two things may happen, depending on the I/O mode that is in effect for the device.

1. If the device is in blocking I/O mode (the default mode), the call blocks until at least one data byte is available (or until some error occurs).
2. If the device is in non-blocking I/O mode, the call returns immediately with $len set to zero.

The I/O mode of the device can be set via a call to Image::Sane::Device->set_io_mode().

  Image::Sane::Device->cancel
This function is used to immediately or as quickly as possible cancel the currently pending operation of the device.

  $device->cancel;

This function can be called at any time (as long as $device is valid) but usually affects long-running operations only (such as image is acquisition). It is safe to call this function asynchronously (e.g., from within a signal handler). It is important to note that completion of this operation does not imply that the currently pending operation has been cancelled. It only guarantees that cancellation has been initiated. Cancellation completes only when the cancelled call throws an exception (typically with a status value of SANE_STATUS_CANCELLED). Since the SANE API does not require any other operations to be re-entrant, this implies that a frontend must not call any other operation until the cancelled operation has returned.

  Image::Sane::Device->set_io_mode
This function is used to set the I/O mode of the device. The I/O mode can be either blocking or non-blocking. If argument $bool is SANE_TRUE, the mode is set to non-blocking mode, otherwise it's set to blocking mode. This function can be called only after a call to Image::Sane::Device->start() has been performed.

  $device->set_io_mode ($bool);

By default, newly opened handles operate in blocking mode. A backend may elect not to support non-blocking I/O mode. In such a case the call throws an exception with the status value SANE_STATUS_UNSUPPORTED. Blocking I/O must be supported by all backends, so calling this function with SANE_FALSE is guaranteed to complete successfully.

  Image::Sane::Device->get_select_fd
This function is used to obtain a (platform-specific) file-descriptor for the device that is readable if and only if image data is available (i.e., when a call to Image::Sane::Device->read() will return at least one byte of data).

  $fd = $device->get_select_fd;

This function can be called only after a call to Image::Sane::Device->start() has been performed and the returned file-descriptor is guaranteed to remain valid for the duration of the current image acquisition (i.e., until Image::Sane::Device->cancel() or Image::Sane::Device->start() is called again or until Image::Sane::Device->read() throws an exception with status SANE_STATUS_EOF). Indeed, a backend must guarantee to close the returned select file descriptor at the point when the next Image::Sane::Device->read() call would throw an exception with SANE_STATUS_EOF. This is necessary to ensure the application can detect when this condition occurs without actually having to call Image::Sane::Device->read().

A backend may elect not to support this operation. In such a case, the function throws an exception with status code SANE_STATUS_UNSUPPORTED.

Note that the only operation supported by the returned file-descriptor is a host operating-system dependent test whether the file-descriptor is readable (e.g., this test can be implemented using select() or poll() under UNIX). If any other operation is performed on the file descriptor, the behaviour of the backend becomes unpredictable. Once the file-descriptor signals ``readable'' status, it will remain in that state until a call to sane_read() is performed. Since many input devices are very slow, support for this operation is strongly encouraged as it permits an application to do other work while image acquisition is in progress.

  Image::Sane::Device->write_pnm_header
This function is a pure-Perl helper function to write a PNM header. It will fetch the current image settings using Image::Sane::Device->get_parameters, if they are not already provided, e.g.:

 $device->write_pnm_header($fh);

or

 $parm = $device->get_parameters;
 $device->write_pnm_header ($fh, $parm->{format},
                                 $parm->{pixels_per_line},
                                 $parm->{lines}, $parm->{depth});

DIAGNOSTICS
If the underlying SANE library returns a status value other than SANE_STATUS_GOOD, an exception is thrown. It is therefore suggested that these are caught using the Try::Tiny module. $_->status and $_->error can be used within the catch{} clause to give the status code and its equivalent string.

CONFIGURATION AND ENVIRONMENT
This module does not require any special configuration or environment, beyond that needed for Perl and SANE.

DEPENDENCIES

Obviously, the SANE library is required, together with the backends for the scanners to be used.
Exception::Class is used for throwing exceptions. It is suggested that these are caught with Try::Tiny.

INCOMPATIBILITIES
None known.

BUGS AND LIMITATIONS
None known.

SEE ALSO
The SANE Standard Reference <http://www.sane-project.org/html> is a handy companion. The Perl bindings follow the C API very closely, and the C reference documentation should be considered the canonical source.

AUTHOR
Jeffrey Ratcliffe, <jffry@posteo.net>

LICENSE AND COPYRIGHT
Copyright (C) 2008--2019 by Jeffrey Ratcliffe

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.5 or, at your option, any later version of Perl 5 you may have available.