NAME

Imager::Cookbook - recipes working with Imager

DESCRIPTION

Various simple and not so simple ways to do things with Imager.

FILES

This is described in detail in Imager::Files.

Reading an image from a file

  my $image = Imager->new;

  $image->read(file=>$filename) or die $image->errstr;

See Imager::Files.

Writing an image to a file

  $image->write(file=>$filename) or die $image->errstr;

Write an animated gif.

  # build an array of images to use in the gif
  my  @images;
  # synthesize the images or read them from files, it doesn't matter
  ...

  # write the gif
  Imager->write_multi({ file=>$filename, type=>'gif' }, @images)
    or die Imager->errstr;

See "Writing an animated GIF" in Imager::Files for a more detailed example.

Reading multiple images from one file

Some formats, like GIF and TIFF support multiple images per file. Use the read_multi() method to read them:

  my @images = Imager->read_multi(file=>$filename)
    or die Imager->errstr;

IMAGE SYNTHESIS

Creating an image

To create a simple RGB image, supply the image width and height to the new() method:

  my $rgb = Imager->new(xsize=>$width, ysize=>$height);

If you also want an alpha channel:

  my $rgb_alpha = Imager->new(xsize=>$width, ysize=>$height, channels=>4);

To make a grayscale image:

  my $gray = Imager->new(xsize=>$width, ysize=>$height, channels=>1);

and a grayscale image with an alpha channel:

  my $gray_alpha = Imager->new(xsize=>$width, ysize=>$height, channels=>2);

When a new image is created this way all samples are set to zero - black for 1 or 3 channel images, transparent black for 2 or 4 channel images.

You can also create paletted images and images with more than 8-bits per channel, see Imager::ImageTypes for more details.

Setting the background of a new image

To set the background of a new image to a solid color, use the box() method with no limits, and filled=>1:

  $image->box(filled=>1, color=>$color);

As always, a color can be specified as an Imager::Color object:

  my $white = Imager::Color->new(255, 255, 255);
  $image->box(filled=>1, color=>$white);

or you supply any single scalar that Imager::Color's new() method accepts as a color description:

  $image->box(filled=>1, color=>'white');
  $image->box(filled=>1, color=>'#FF0000');
  $image->box(filled=>1, color=>[ 255, 255, 255 ]);

You can also fill the image with a fill object:

  use Imager::Fill;
  # create the fill object
  my $fill = Imager::Fill->new(hatch=>'check1x1')
  $image->box(fill=>$fill);

  # let Imager create one automatically
  $image->box(fill=>{ hatch=>'check1x1' });

See Imager::Fill for information on Imager's fill objects.

WORLD WIDE WEB

As with any CGI script it's up to you to validate data and set limits on any parameters supplied to Imager.

For example, if you allow the caller to set the size of an output image you should limit the size to prevent the client from specifying an image size that will consume all available memory.

This is beside any any other controls you need over access to data.

See CGI for a module useful for processing CGI submitted data.

Returning an image from a CGI script

This is similar to writing to a file, but you also need to supply the information needed by the web browser to identify the file format:

  my $img = ....; # create the image and generate the contents
  print "Content-Type: image/png\n\n";
  binmode STDOUT;
  $img->write(fd=>fileno(STDOUT), type=>'png')
    or die $img->errstr;

You need to set the Content-Type header depending on the file format you send to the web browser.

If you want to supply a content-length header, write the image to a scalar as a buffer:

  my $img = ....; # create the image and generate the contents
  my $data;
  $img->write(type=>'png', data=>\$data)
    or die $img->errstr;
  print "Content-Type: image/png\n";
  print "Content-Length: ",length($data),"\n\n";
  binmode STDOUT;
  print $data;

See samples/samp-scale.cgi and samples/samp-image.cgi for a couple of simple examples of producing an image from CGI.

Inserting a CGI image in a page

There's occasionally confusion on how to display an image generated by Imager in a page generated by a CGI.

Your web browser handles this process as two requests, one for the HTML page, and another for the image itself.

Each request needs to perform validation since an attacker can control the values supplied to both requests.

How you make the data available to the image generation code depends on your application.

See samples/samp-form.cgi and samples/samp-image.cgi in the Imager distribution for one approach. The POD in samp-form.cgi also discusses some of the issues involved.

Parsing an image posted via CGI

WARNING: file format attacks have become a common attack vector, make sure you have up to date image file format libraries, otherwise trying to parse uploaded files, whether with Imager or some other tool, may result in a remote attacker being able to run their own code on your system. Currently Imager makes no attempt to place size limits on a read image file. This may result in consumption of large amounts of memory. Future versions of Imager may provide mechanisms to limit the sizes of images read from files.

If your HTML form uses the correct magic, it can upload files to your CGI script, in particular, you need to use method="post" and enctype="multipart/form-data" in the form tag, and use type="file" in the input, for example:

  <form action="/cgi-bin/yourprogram" method="post" 
        enctype="multipart/form-data">
    <input type="file" name="myimage" />
    <input type="submit value="Upload Image" />
  </form>

To process the form:

1. first check that the user supplied a file

2. get the file handle

3. have Imager read the image

  # returns the client's name for the file, don't open this locally
  my $cgi = CGI->new;
  # 1. check the user supplied a file
  my $filename = $cgi->param('myimage');
  if ($filename) {
    # 2. get the file handle
    my $fh = $cgi->upload('myimage');
    if ($fh) {
      binmode $fh;
      
      # 3. have Imager read the image
      my $img = Imager->new;
      if ($img->read(fh=>$fh)) {
        # we can now process the image
      }
    }
    # else, you probably have an incorrect form or input tag
  }
  # else, the user didn't select a file

See samples/samp-scale.cgi and samples/samp-tags.cgi in the Imager distribution for example code.

DRAWING

TEXT

Drawing text

Aligning text

Measuring text

Word wrapping text

METADATA

Image spatial resolution.

Keywords: DPI

AUTHOR

Tony Cook <tony@develop-help.com>

SEE ALSO

Imager, Imager::Files, Imager::Draw.

cpanm Imager

perl -MCPAN -e shell
install Imager