Arnar Mar Hrafnkelsson > Imager-0.43 > Imager::Files

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NAME ^

Imager::Files - working with image files

SYNOPSIS ^

  my $img = ...;
  $img->write(file=>$filename, type=>$type)
    or die "Cannot write: ",$img->errstr;

  $img = Imager->new;
  $img->read(file=>$filename, type=>$type)
    or die "Cannot read: ", $img->errstr;

  Imager->write_multi({ file=> $filename, ... }, @images)
    or die "Cannot write: ", Imager->errstr;

  my @imgs = Imager->read_multi(file=>$filename)
    or die "Cannot read: ", Imager->errstr;

DESCRIPTION ^

You can read and write a variety of images formats, assuming you have the appropriate libraries, and images can be read or written to/from files, file handles, file descriptors, scalars, or through callbacks.

To see which image formats Imager is compiled to support the following code snippet is sufficient:

  use Imager;
  print join " ", keys %Imager::formats;

This will include some other information identifying libraries rather than file formats.

Reading writing to and from files is simple, use the read() method to read an image:

  my $img = Imager->new;
  $img->read(file=>$filename, type=>$type)
    or die "Cannot read $filename: ", $img->errstr;

and the write() method to write an image:

  $img->write(file=>$filename, type=>$type)
    or die "Cannot write $filename: ", $img->errstr;

If you're reading from a format that supports multiple images per file, use the read_multi() method:

  my @imgs = Imager->read_multi(file=>$filename, type=>$type)
    or die "Cannot read $filename: ", Imager->errstr;

and if you want to write multiple images to a single file use the write_multi() method:

  Imager->write_multi({ file=> $filename, type=>$type }, @images)
    or die "Cannot write $filename: ", Imager->errstr;

If the filename includes an extension that Imager recognizes, then you don't need the type, but you may want to provide one anyway. See "Guessing types" for information on controlling this recognition.

The type parameter is a lowercase representation of the file type, and can be any of the following:

  bmp   Windows BitMaP (BMP)
  gif   Graphics Interchange Format (GIF)
  jpeg  JPEG/JFIF
  png   Portable Network Graphics (PNG)
  pnm   Portable aNyMap (PNM)
  raw   Raw
  rgb   SGI .rgb files
  tga   TARGA
  tiff  Tagged Image File Format (TIFF)

When you read an image, Imager may set some tags, possibly including information about the spatial resolution, textual information, and animation information. See "Tags" in Imager::ImageTypes for specifics.

Input and output

When reading or writing you can specify one of a variety of sources or targets:

file

The file parameter is the name of the image file to be written to or read from. If Imager recognizes the extension of the file you do not need to supply a type.

fh

fh is a file handle, typically either returned from <IO::File-new()>>, or a glob from an open call. You should call binmode on the handle before passing it to Imager.

Imager will set the handle to autoflush to make sure any buffered data is flushed , since Imager will write to the file descriptor (from fileno()) rather than writing at the perl level.

fd

fd is a file descriptor. You can get this by calling the fileno() function on a file handle, or by using one of the standard file descriptor numbers.

If you get this from a perl file handle, you may need to flush any buffered output, otherwise it may appear in the output stream after the image.

data

When reading data, data is a scalar containing the image file data, when writing, data is a reference to the scalar to save the image file data too. For GIF images you will need giflib 4 or higher, and you may need to patch giflib to use this option for writing.

callback

Imager will make calls back to your supplied coderefs to read, write and seek from/to/through the image file.

When reading from a file you can use either callback or readcb to supply the read callback, and when writing callback or writecb to supply the write callback.

When writing you can also supply the maxbuffer option to set the maximum amount of data that will be buffered before your write callback is called. Note: the amount of data supplied to your callback can be smaller or larger than this size.

The read callback is called with 2 parameters, the minimum amount of data required, and the maximum amount that Imager will store in it's C level buffer. You may want to return the minimum if you have a slow data source, or the maximum if you have a fast source and want to prevent many calls to your perl callback. The read data should be returned as a scalar.

Your write callback takes exactly one parameter, a scalar containing the data to be written. Return true for success.

The seek callback takes 2 parameters, a POSITION, and a WHENCE, defined in the same way as perl's seek function.

You can also supply a closecb which is called with no parameters when there is no more data to be written. This could be used to flush buffered data.

Guessing types

Imager uses the code reference in $Imager::FORMATGUESS to guess the file type when you don't supply a type. The code reference is called with a single parameter, the filename of the file. The code reference is only called if a file parameter is supplied to the file access method.

Return either a valid Imager file type, or undef.

  # I'm writing jpegs to weird filenames
  local $Imager::FORMATGUESS = sub { 'jpeg' };

TYPE SPECIFIC INFORMATION ^

The different image formats can write different image type, and some have different options to control how the images are written.

When you call write() or write_multi() with an option that has the same name as a tag for the image format you're writing, then the value supplied to that option will be used to set the corresponding tag in the image. Depending on the image format, these values will be used when writing the image.

This replaces the previous options that were used when writing GIF images. Currently if you use an obsolete option, it will be converted to the equivalent tag and Imager will produced a warning. You can suppress these warnings by calling the Imager::init() function with the warn_obsolete option set to false:

  Imager::init(warn_obsolete=>0);

At some point in the future these obsolete options will no longer be supported.

PNM (Portable aNy Map)

Imager can write PGM (Portable Gray Map) and PPM (Portable PixMaps) files, depending on the number of channels in the image. Currently the images are written in binary formats. Only 1 and 3 channel images can be written, including 1 and 3 channel paletted images.

  $img->write(file=>'foo.ppm') or die $img->errstr;

Imager can read both the ASCII and binary versions of each of the PBM (Portable BitMap), PGM and PPM formats.

  $img->read(file=>'foo.ppm') or die $img->errstr;

PNM does not support the spatial resolution tags.

JPEG

You can supply a jpegquality parameter (0-100) when writing a JPEG file, which defaults to 75%. Only 1 and 3 channel images can be written, including 1 and 3 channel paletted images.

  $img->write(file=>'foo.jpg', jpegquality=>90) or die $img->errstr;

Imager will read a grayscale JPEG as a 1 channel image and a color JPEG as a 3 channel image.

  $img->read(file=>'foo.jpg') or die $img->errstr;

PNM does not support the spatial resolution tags.

GIF (Graphics Interchange Format)

When writing one of more GIF images you can use the same Quantization Options as you can when converting an RGB image into a paletted image.

When reading a GIF all of the sub-images are combined using the screen size and image positions into one big image, producing an RGB image. This may change in the future to produce a paletted image where possible.

When you read a single GIF with $img->read() you can supply a reference to a scalar in the colors parameter, if the image is read the scalar will be filled with a reference to an anonymous array of Imager::Color objects, representing the palette of the image. This will be the first palette found in the image. If you want the palettes for each of the images in the file, use read_multi() and use the getcolors() method on each image.

GIF does not support the spatial resolution tags.

Imager will set the following tags in each image when reading, and can use most of them when writing to GIF:

gif_left

the offset of the image from the left of the "screen" ("Image Left Position")

gif_top

the offset of the image from the top of the "screen" ("Image Top Position")

gif_interlace

non-zero if the image was interlaced ("Interlace Flag")

gif_screen_width
gif_screen_height

the size of the logical screen. When writing this is used as the minimum. If any image being written would extend beyond this the screen size is extended. ("Logical Screen Width", "Logical Screen Height").

When writing this is used as a minimum, if the combination of the image size and the image's gif_left and gif_top is beyond this size then the screen size will be expanded.

gif_local_map

Non-zero if this image had a local color map. If set for an image when writing the image is quantized separately from the other images in the file.

gif_background

The index in the global colormap of the logical screen's background color. This is only set if the current image uses the global colormap. You can set this on write too, but for it to choose the color you want, you will need to supply only paletted images and set the gif_eliminate_unused tag to 0.

gif_trans_index

The index of the color in the colormap used for transparency. If the image has a transparency then it is returned as a 4 channel image with the alpha set to zero in this palette entry. This value is not used when writing. ("Transparent Color Index")

gif_trans_color

A reference to an Imager::Color object, which is the colour to use for the palette entry used to represent transparency in the palette. You need to set the transp option (see "Quantization options") for this value to be used.

gif_delay

The delay until the next frame is displayed, in 1/100 of a second. ("Delay Time").

gif_user_input

whether or not a user input is expected before continuing (view dependent) ("User Input Flag").

gif_disposal

how the next frame is displayed ("Disposal Method")

gif_loop

the number of loops from the Netscape Loop extension. This may be zero.

gif_comment

the first block of the first gif comment before each image.

gif_eliminate_unused

If this is true, when you write a paletted image any unused colors will be eliminated from its palette. This is set by default.

Where applicable, the ("name") is the name of that field from the GIF89 standard.

The following gif writing options are obsolete, you should set the corresponding tag in the image, either by using the tags functions, or by supplying the tag and value as options.

gif_each_palette

Each image in the gif file has it's own palette if this is non-zero. All but the first image has a local colour table (the first uses the global colour table.

Use gif_local_map in new code.

interlace

The images are written interlaced if this is non-zero.

Use gif_interlace in new code.

gif_delays

A reference to an array containing the delays between images, in 1/100 seconds.

Use gif_delay in new code.

gif_positions

A reference to an array of references to arrays which represent screen positions for each image.

New code should use the gif_left and gif_top tags.

gif_loop_count

If this is non-zero the Netscape loop extension block is generated, which makes the animation of the images repeat.

This is currently unimplemented due to some limitations in giflib.

TIFF (Tagged Image File Format)

Imager can write images to either paletted or RGB TIFF images, depending on the type of the source image. Currently if you write a 16-bit/sample or double/sample image it will be written as an 8-bit/sample image. Only 1 or 3 channel images can be written.

If you are creating images for faxing you can set the class parameter set to fax. By default the image is written in fine mode, but this can be overridden by setting the fax_fine parameter to zero. Since a fax image is bi-level, Imager uses a threshold to decide if a given pixel is black or white, based on a single channel. For greyscale images channel 0 is used, for color images channel 1 (green) is used. If you want more control over the conversion you can use $img->to_paletted() to product a bi-level image. This way you can use dithering:

  my $bilevel = $img->to_paletted(colors=>[ NC(0,0,0), NC(255,255,255) ],
                                  make_colors => 'none',
                                  translate => 'errdiff',
                                  errdiff => 'stucki');
class

If set to 'fax' the image will be written as a bi-level fax image.

fax_fine

By default when class is set to 'fax' the image is written in fine mode, you can select normal mode by setting fax_fine to 0.

Imager should be able to read any TIFF image you supply. Paletted TIFF images are read as paletted Imager images, since paletted TIFF images have 16-bits/sample (48-bits/color) this means the bottom 8-bits are lost, but this shouldn't be a big deal. Currently all direct color images are read at 8-bits/sample.

TIFF supports the spatial resolution tags. See the tiff_resolutionunit tag for some extra options.

The following tags are set in a TIFF image when read, and can be set to control output:

tiff_resolutionunit

The value of the ResolutionUnit tag. This is ignored on writing if the i_aspect_only tag is non-zero.

The i_xres and i_yres tags are expressed in pixels per inch no matter tha value of this tag, they will be converted to/from the value stored in the TIFF file.

tiff_documentname
tiff_imagedescription
tiff_make
tiff_model
tiff_pagename
tiff_software
tiff_datetime
tiff_artist
tiff_hostcomputer

Various strings describing the image. tiff_datetime must be formatted as "YYYY:MM:DD HH:MM:SS". These correspond directly to the mixed case names in the TIFF specification. These are set in images read from a TIFF and saved when writing a TIFF image.

BMP (BitMaP)

Imager can write 24-bit RGB, and 8, 4 and 1-bit per pixel paletted Windows BMP files. Currently you cannot write compressed BMP files with Imager.

Imager can read 24-bit RGB, and 8, 4 and 1-bit perl pixel paletted Windows BMP files. There is some support for reading 16-bit per pixel images, but I haven't found any for testing.

BMP has no support for multi-image files.

BMP files support the spatial resolution tags, but since BMP has no support for storing only an aspect ratio, if i_aspect_only is set when you write the i_xres and i_yres values are scaled so the smaller it 72 DPI.

The following tags are set when you read an image from a BMP file:

bmp_compression

The type of compression, if any. This can be any of the following values:

BI_RGB (0)

Uncompressed.

BI_RLE8 (1)

8-bits/pixel paletted value RLE compression.

BI_RLE4 (2)

4-bits/pixel paletted value RLE compression.

BI_BITFIELDS (3)

Packed RGB values.

bmp_important_colors

The number of important colors as defined by the writer of the image.

TGA (TarGA)

When storing targa images rle compression can be activated with the 'compress' parameter, the 'idstring' parameter can be used to set the targa comment field and the 'wierdpack' option can be used to use the 15 and 16 bit targa formats for rgb and rgba data. The 15 bit format has 5 of each red, green and blue. The 16 bit format in addition allows 1 bit of alpha. The most significant bits are used for each channel.

Tags:

tga_idstring
tga_bitspp
compressed

RAW

When reading raw images you need to supply the width and height of the image in the xsize and ysize options:

  $img->read(file=>'foo.raw', xsize=>100, ysize=>100)
    or die "Cannot read raw image\n";

If your input file has more channels than you want, or (as is common), junk in the fourth channel, you can use the datachannels and storechannels options to control the number of channels in your input file and the resulting channels in your image. For example, if your input image uses 32-bits per pixel with red, green, blue and junk values for each pixel you could do:

  $img->read(file=>'foo.raw', xsize=>100, ysize=>100, datachannels=>4,
             storechannels=>3)
    or die "Cannot read raw image\n";

Normally the raw image is expected to have the value for channel 1 immediately following channel 0 and channel 2 immediately following channel 1 for each pixel. If your input image has all the channel 0 values for the first line of the image, followed by all the channel 1 values for the first line and so on, you can use the interleave option:

  $img->read(file=>'foo.raw', xsize=100, ysize=>100, interleave=>1)
    or die "Cannot read raw image\n";

EXAMPLES ^

Producing an image from a CGI script

Once you have an image the basic mechanism is:

  1. set STDOUT to autoflush
  2. output a content-type header, and optionally a content-length header
  3. put STDOUT into binmode
  4. call write() with the fd or fh parameter. You will need to provide the type parameter since
  # write an image from a CGI script
  # using CGI.pm
  use CGI qw(:standard);
  $| = 1;
  binmode STDOUT;
  print header(-type=>'image/gif');
  $img->write(type=>'gif', fd=>fileno(STDOUT))
    or die $img->errstr;

If you want to send a content length you can send the output to a scalar to get the length:

  my $data;
  $img->write(type=>'gif', data=>\$data)
    or die $img->errstr;
  binmode STDOUT;
  print header(-type=>'image/gif', -content_length=>length($data));
  print $data;

Writing an animated GIF

The basic idea is simple, just use write_multi():

  my @imgs = ...;
  Imager->write_multi({ file=>$filename, type=>'gif' }, @imgs);

If your images are RGB images the default quantization mechanism will produce a very good result, but can take a long time to execute. You could either use the standard webmap:

  Imager->write_multi({ file=>$filename, 
                        type=>'gif',
                        make_colors=>'webmap' },
                      @imgs);

or use a median cut algorithm to built a fairly optimal color map:

  Imager->write_multi({ file=>$filename,
                        type=>'gif',
                        make_colors=>'mediancut' },
                      @imgs);

By default all of the images will use the same global colormap, which will produce a smaller image. If your images have significant color differences, you may want to generate a new palette for each image:

  Imager->write_multi({ file=>$filename,
                        type=>'gif',
                        make_colors=>'mediancut',
                        gif_local_map => 1 },
                      @imgs);

which will set the gif_local_map tag in each image to 1. Alternatively, if you know only some images have different colors, you can set the tag just for those images:

  $imgs[2]->settag(name=>'gif_local_map', value=>1);
  $imgs[4]->settag(name=>'gif_local_map', value=>1);

and call write_multi() without a gif_local_map parameter, or supply an arrayref of values for the tag:

  Imager->write_multi({ file=>$filename,
                        type=>'gif',
                        make_colors=>'mediancut',
                        gif_local_map => [ 0, 0, 1, 0, 1 ] },
                      @imgs);

Other useful parameters include gif_delay to control the delay between frames and transp to control transparency.

Reading tags after reading an image

This is pretty simple:

  # print the author of a TIFF, if any
  my $img = Imager->new;
  $img->read(file=>$filename, type='tiff') or die $img->errstr;
  my $author = $img->tags(name=>'tiff_author');
  if (defined $author) {
    print "Author: $author\n";
  }

BUGS ^

When saving Gif images the program does NOT try to shave of extra colors if it is possible. If you specify 128 colors and there are only 2 colors used - it will have a 128 colortable anyway.

SEE ALSO ^

Imager(3)

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