Imager::ImageTypes - image models for Imager |
Imager::ImageTypes - image models for Imager
use Imager;
$img = Imager->new(); # Empty image (size is 0 by 0) $img->open(file=>'lena.png',type=>'png'); # Read image from file
$img = Imager->new(xsize=>400, ysize=>300); # RGB data
$img = Imager->new(xsize=>400, ysize=>300, # Grayscale channels=>1); #
$img = Imager->new(xsize=>400, ysize=>300, # RGB with alpha channels=>4); # $img = Imager->new(xsize=>200, ysize=>200, type=>'paletted'); # paletted image $img = Imager->new(xsize=>200, ysize=>200, bits=>16); # 16 bits/channel rgb $img = Imager->new(xsize=>200, ysize=>200, bits=>'double'); # 'double' floating point # per channel
$img->img_set(xsize=>500, ysize=>500, # reset the image object channels=>4);
# Example getting information about an Imager object
print "Image information:\n"; print "Width: ", $img->getwidth(), "\n"; print "Height: ", $img->getheight(), "\n"; print "Channels: ", $img->getchannels(), "\n"; print "Bits/Channel: ", $img->bits(), "\n"; print "Virtual: ", $img->virtual() ? "Yes" : "No", "\n"; my $colorcount = $img->getcolorcount(maxcolors=>512); print "Actual number of colors in image: "; print defined($colorcount) ? $colorcount : ">512", "\n"; print "Type: ", $img->type(), "\n";
if ($img->type() eq 'direct') { print "Modifiable Channels: "; print join " ", map { ($img->getmask() & 1<<$_) ? $_ : () } 0..$img->getchannels(); print "\n"; } else { # palette info my $count = $img->colorcount; @colors = $img->getcolors(); print "Palette size: $count\n"; my $mx = @colors > 4 ? 4 : 0+@colors; print "First $mx entries:\n"; for (@colors[0..$mx-1]) { my @res = $_->rgba(); print "(", join(", ", @res[0..$img->getchannels()-1]), ")\n"; } } my @tags = $img->tags(); if (@tags) { print "Tags:\n"; for(@tags) { print shift @$_, ": ", join " ", @$_, "\n"; } } else { print "No tags in image\n"; } =head1 DESCRIPTION
Imager supports two basic models of image:
Direct color or paletted images can have 1 to 4 samples per color stored. Imager treats these as follows:
Direct color images can have sample sizes of 8-bits per sample, 16-bits per sample or a double precision floating point number per sample (64-bits on many systems).
Paletted images are always 8-bits/sample.
To query an existing image about it's parameters see the bits()
,
type()
, getwidth()
, getheight()
, getchannels()
and
virtual()
methods.
The coordinate system in Imager has the origin in the upper left corner, see the Imager::Draw manpage for details.
The alpha channel when one is present is considered unassociated - ie the color data has not been scaled by the alpha channel. Note that not all code follows this (recent) rule, but will over time.
new()
$img = Imager->new(); $img->read(file=>"alligator.ppm") or die $img->errstr;
Here new()
creates an empty image with width and height of zero.
It's only useful for creating an Imager object to call the read()
method on later.
%opts = (xsize=>300, ysize=>200); $img = Imager->new(%opts); # create direct mode RGBA image $img = Imager->new(%opts, channels=>4); # create direct mode RGBA image
You can also read a file from new():
$img = Imager->new(file => "someimage.png");
The parameters for new are:
xsize
, ysize
- Defines the width and height in pixels of the
image. These must be positive.
If not supplied then only placeholder object is created, which can be
supplied to the read()
or img_set()
methods.
channels
- The number of channels for the image. Default 3. Valid
values are from 1 to 4.
model
- this overrides the value, if any, supplied for channels
.
This can be one of gray
, graya
, rgb
or rgba
.
bits
- The storage type for samples in the image. Default: 8.
Valid values are:
8
- One byte per sample. 256 discrete values.
16
- 16-bits per sample, 65536 discrete values.
double
- one C double per sample.
Note: you can use any Imager function on any sample size image.
Paletted images always use 8 bits/sample.
type
- either 'direct'
or 'paletted'
. Default: 'direct'
.
Direct images store color values for each pixel.
Paletted images keep a table of up to 256 colors called the palette, each pixel is represented as an index into that table.
In most cases when working with Imager you will want to use the
direct
image type.
If you draw on a paletted
image with a color not in the image's
palette then Imager will transparently convert it to a direct
image.
maxcolors
- the maximum number of colors in a paletted image.
Default: 256. This must be in the range 1 through 256.
file
, fh
, fd
, callback
, readcb
- specify a file name,
filehandle, file descriptor or callback to read image data from. See
the Imager::Files manpage for details. The typical use is:
my $im = Imager->new(file => $filename);
filetype
- treated as the file format parameter, as for type
with the read()
method, eg:
my $im = Imager->new(file => $filename, filetype => "gif");
In most cases Imager will detect the file's format itself.
In the simplest case just supply the width and height of the image:
# 8 bit/sample, RGB image my $img = Imager->new(xsize => $width, ysize => $height);
or if you want an alpha channel:
# 8 bits/sample, RGBA image my $img = Imager->new(xsize => $width, ysize => $height, channels=>4);
Note that it is possible for image creation to fail, for example if channels is out of range, or if the image would take too much memory.
To create paletted images, set the 'type' parameter to 'paletted':
$img = Imager->new(xsize=>200, ysize=>200, type=>'paletted');
which creates an image with a maximum of 256 colors, which you can
change by supplying the maxcolors
parameter.
For improved color precision you can use the bits parameter to specify 16 bit per channel:
$img = Imager->new(xsize=>200, ysize=>200, channels=>3, bits=>16);
or for even more precision:
$img = Imager->new(xsize=>200, ysize=>200, channels=>3, bits=>'double');
to get an image that uses a double for each channel.
Note that as of this writing all functions should work on images with more than 8-bits/channel, but many will only work at only 8-bit/channel precision.
If you want an empty Imager object to call the read()
method on, just
call new()
with no parameters:
my $img = Imager->new; $img->read(file=>$filename) or die $img->errstr;
Though it's much easier now to just call new()
with a file
parameter:
my $img = Imager->new(file => $filename) or die Imager->errstr;
If none of xsize
, ysize
, file
, fh
, fd
, callback
,
readcb
or data
is supplied, and other parameters are supplied
Imager->new
will return failure rather than returning an empty
image object.
img_set()
convert()
method.
$img->img_set(xsize=>500, ysize=>500, channels=>4);
This takes exactly the same parameters as the new()
method.
These return basic attributes of an image object.
getwidth()
print "Image width: ", $img->getwidth(), "\n";
The getwidth()
method returns the width of the image. This value
comes either from new()
with xsize
, ysize
parameters or from
reading data from a file with read()
. If called on an image that
has no valid data in it like Imager->new()
returns, the return
value of getwidth()
is undef.
getheight()
print "Image height: ", $img->getheight(), "\n";
Same details apply as for getwidth().
getchannels()
print "Image has ",$img->getchannels(), " channels\n";
Returns the number of channels in an image.
Note: previously the number of channels in an image mapped directly to the color model of the image, ie a 4 channel image was always RGBA. This may change in a future release of Imager.
Returns an empty list if the image object is not initialized.
colorchannels()
Currently this is always 1 or 3, but may be 0 for some rare images in a future version of Imager.
Returns an empty list if the image object is not initialized.
colormodel()
By default this is returned as a string, one of unknown
, gray
,
graya
, rgb
or rgba
.
If you call colormodel()
with a true numeric parameter:
my $model = $img->colormodel(numeric => 1);
then the color model is returned as a number, mapped as follows:
Numeric String ------- ------ 0 unknown 1 gray 2 graya 3 rgb 4 rgba
alphachannel()
This is 1 for grayscale images with alpha, 3 for RGB images with alpha
and will return undef
for all other images.
Returns an empty list if the image object is not initialized.
bits()
bits()
method retrieves the number of bits used to represent each
channel in a pixel, 8 for a normal image, 16 for 16-bit image and
'double' for a double/channel image.
if ($img->bits eq 8) { # fast but limited to 8-bits/sample } else { # slower but more precise }
Returns an empty list if the image object is not initialized.
type()
type()
method returns either 'direct' for direct color images or
'paletted' for paletted images.
if ($img->type eq 'paletted') { # print the palette for my $color ($img->getcolors) { print join(",", $color->rgba), "\n"; } }
Returns an empty list if the image object is not initialized.
virtual()
virtual()
method returns non-zero if the image contains no actual
pixels, for example masked images.
This may also be used for non-native Imager images in the future, for example, for an Imager object that draws on an SDL surface.
is_bilevel()
In scalar context, returns true if the image is bi-level.
In list context returns a list:
($is_bilevel, $zero_is_white) = $img->is_bilevel;
An image is considered bi-level, if all of the following are true:
If a real bi-level organization image is ever added to Imager, this function will return true for that too.
Returns an empty list if the image object is not initialized.
Direct images store the color value directly for each pixel in the image.
getmask()
@rgbanames = qw( red green blue alpha ); my $mask = $img->getmask(); print "Modifiable channels:\n"; for (0..$img->getchannels()-1) { print $rgbanames[$_],"\n" if $mask & 1<<$_; }
getmask()
is used to fetch the current channel mask. The mask
determines what channels are currently modifiable in the image. The
channel mask is an integer value, if the i-th
least significant bit
is set the i-th
channel is modifiable. eg. a channel mask of 0x5
means only channels 0 and 2 are writable.
setmask()
$mask = $img->getmask(); $img->setmask(mask=>8); # modify alpha only
...
$img->setmask(mask=>$mask); # restore previous mask
setmask()
is used to set the channel mask of the image. See
getmask() for details.
Paletted images keep an array of up to 256 colors, and each pixel is stored as an index into that array.
In general you can work with paletted images in the same way as RGB images, except that if you attempt to draw to a paletted image with a color that is not in the image's palette, the image will be converted to an RGB image. This means that drawing on a paletted image with anti-aliasing enabled will almost certainly convert the image to RGB.
Palette management takes place through addcolors()
, setcolors()
,
getcolors()
and findcolor()
:
addcolors()
addcolors()
method:
my @colors = ( Imager::Color->new(255, 0, 0), Imager::Color->new(0, 255, 0) ); my $index = $img->addcolors(colors=>\@colors);
The return value is the index of the first color added, or undef if adding the colors would overflow the palette.
The only parameter is colors
which must be a reference to an array
of Imager::Color objects.
setcolors()
$img->setcolors(start=>$start, colors=>\@colors);
Once you have colors in the palette you can overwrite them with the
setcolors()
method: setcolors()
returns true on success.
Parameters:
getcolors()
getcolors()
method:
# get the whole palette my @colors = $img->getcolors(); # get a single color my $color = $img->getcolors(start=>$index); # get a range of colors my @colors = $img->getcolors(start=>$index, count=>$count);
findcolor()
my $index = $img->findcolor(color=>$color);
which returns undef on failure, or the index of the color.
Parameter:
colorcount()
my $count = $img->colorcount;
maxcolors()
my $maxcount = $img->maxcolors;
getcolorcount()
The amount of memory used by this is proportional to the number of
colors present in the image, so to avoid using too much memory you can
supply a maxcolors()
parameter to limit the memory used.
Note: getcolorcount()
treats the image as an 8-bit per sample image.
maxcolors
- the maximum number of colors to
return. Default: unlimited.
if (defined($img->getcolorcount(maxcolors=>512)) { print "Less than 512 colors in image\n"; }
getcolorusagehash()
maxcolors
- the maximum number of colors
to return. Default: unlimited.
Returns a reference to a hash where the keys are the raw color as bytes, and the values are the counts for that color.
The alpha channel of the image is ignored. If the image is gray scale then the hash keys will each be a single character.
my $colors = $img->getcolorusagehash; my $blue_count = $colors->{pack("CCC", 0, 0, 255)} || 0; print "#0000FF used $blue_count times\n";
getcolorusage()
maxcolors
- the maximum number of colors
to return. Default: unlimited.
Returns a list of the color frequencies in ascending order.
my @counts = $img->getcolorusage; print "The most common color is used $counts[0] times\n";
Warning: if you draw on a paletted image with colors that aren't in the palette, the image will be internally converted to a normal image.
to_paletted()
to_paletted()
method:
$palimg = $img->to_paletted(\%opts)
where %opts contains the options specified under Quantization options.
# convert to a paletted image using the web palette # use the closest color to each pixel my $webimg = $img->to_paletted({ make_colors => 'webmap' });
# convert to a paletted image using a fairly optimal palette # use an error diffusion dither to try to reduce the average error my $optimag = $img->to_paletted({ make_colors => 'mediancut', translate => 'errdiff' });
to_rgb8()
$rgbimg = $img->to_rgb8;
No parameters.
to_rgb16()
$rgbimg = $img->to_rgb16;
No parameters.
to_rgb_double()
$rgbimg = $img->to_rgb_double;
No parameters.
masked()
In the discussion below there are 3 image objects involved:
masked()
method. Any
writes to this image are written to the target image, assuming the
mask image allows it.
the mask image - the image that protects writes to the target image.
Supplied as the mask
parameter to the masked()
method.
the target image - the image you called the masked()
method on. Any
writes to the masked image end up on this image.
Parameters:
Masked images let you control which pixels are modified in an underlying image. Where the first channel is completely black in the mask image, writes to the underlying image are ignored.
For example, given a base image called $img:
my $mask = Imager->new(xsize=>$img->getwidth, ysize=>$img->getheight, channels=>1); # ... draw something on the mask my $maskedimg = $img->masked(mask=>$mask);
# now draw on $maskedimg and it will only draw on areas of $img # where $mask is non-zero in channel 0.
You can specify the region of the underlying image that is masked using the left, top, right and bottom options.
If you just want a subset of the image, without masking, just specify the region without specifying a mask. For example:
# just work with a 100x100 region of $img my $maskedimg = $img->masked(left => 100, top=>100, right=>200, bottom=>200);
make_palette()
my @colors = Imager->make_palette(\%opts, @images);
You must supply at least one image, even if the make_colors
parameter produces a fixed palette.
On failure returns no colors and you can check Imager->errstr
.
Image tags contain meta-data about the image, ie. information not stored as pixels of the image.
At the perl level each tag has a name or code and a value, which is an integer or an arbitrary string. An image can contain more than one tag with the same name or code, but having more than one tag with the same name is discouraged.
You can retrieve tags from an image using the tags()
method, you can
get all of the tags in an image, as a list of array references, with
the code or name of the tag followed by the value of the tag.
Imager's support for fairly limited, for access to pretty much all image metadata you may want to try the Image::ExifTool manpage.
tags()
With no parameters, retrieves a list array references, each containing a name and value: all tags in the image:
# get a list of ( [ name1 => value1 ], [ name2 => value2 ] ... ) my @alltags = $img->tags; print $_->[0], ":", $_->[1], "\n" for @all_tags;
# or put it in a hash, but this will lose duplicates my %alltags = map @$_, $img->tags;
in scalar context this returns the number of tags:
my $num_tags = $img->tags;
or you can get all tags values for the given name:
my @namedtags = $img->tags(name => $name);
in scalar context this returns the first tag of that name:
my $firstnamed = $img->tags(name => $name);
or a given code:
my @tags = $img->tags(code=>$code);
addtag()
addtag()
method, either by name:
my $index = $img->addtag(name=>$name, value=>$value);
or by code:
my $index = $img->addtag(code=>$code, value=>$value);
deltag()
deltag()
method, either by index:
$img->deltag(index=>$index);
or by name:
$img->deltag(name=>$name);
or by code:
$img->deltag(code=>$code);
In each case deltag()
returns the number of tags deleted.
settag()
settag()
replaces any existing tags with a new tag. This is
equivalent to calling deltag()
then addtag().
Many tags are only meaningful for one format. GIF looping information is pretty useless for JPEG for example. Thus, many tags are set by only a single reader or used by a single writer. For a complete list of format specific tags see the Imager::Files manpage.
Since tags are a relatively new addition their use is not wide spread but eventually we hope to have all the readers for various formats set some standard information.
i_xres
, i_yres
- The spatial resolution of the image in pixels per inch. If the
image format uses a different scale, eg. pixels per meter, then this
value is converted. A floating point number stored as a string.
# our image was generated as a 300 dpi image $img->settag(name => 'i_xres', value => 300); $img->settag(name => 'i_yres', value => 300);
# 100 pixel/cm for a TIFF image $img->settag(name => 'tiff_resolutionunit', value => 3); # RESUNIT_CENTIMETER # convert to pixels per inch, Imager will convert it back $img->settag(name => 'i_xres', value => 100 * 2.54); $img->settag(name => 'i_yres', value => 100 * 2.54);
i_aspect_only
- If this is
non-zero then the values in i_xres and i_yres are treated as a ratio
only. If the image format does not support aspect ratios then this is
scaled so the smaller value is 72 DPI.
i_incomplete
- If this tag is
present then the whole image could not be read. This isn't
implemented for all images yet, and may not be.
i_lines_read
- If
i_incomplete
is set then this tag may be set to the number of
scan lines successfully read from the file. This can be used to decide
whether an image is worth processing.
i_format - The file format this file
was read from.
i_background - used when writing
an image with an alpha channel to a file format that doesn't support
alpha channels. The write
method will convert a normal color
specification like ``#FF0000'' into a color object for you, but if you
set this as a tag you will need to format it like
color(
red,
green,
blue)
, eg color(255,0,0).
i_comment
- used when reading or writing several image
formats. If the format has only one text field it will be read into
the i_comment
tag or written to the file.
These options can be specified when calling
to_paletted() in the Imager::ImageTypes manpage, write_multi()
for GIF files, when
writing a single image with the gifquant
option set to gen
, or for
direct calls to i_writegif_gen()
and i_writegif_callback().
colors
- An arrayref of colors that are fixed. Note that some
color generators will ignore this. If this is supplied it will be
filled with the color table generated for the image.
transp
- The type of transparency processing to perform for images
with an alpha channel where the output format does not have a proper
alpha channel (eg. GIF). This can be any of:
none
- No transparency processing is done. (default)
threshold
- pixels more transparent than tr_threshold
are
rendered as transparent.
errdiff
- An error diffusion dither is done on the alpha channel.
Note that this is independent of the translation performed on the
color channels, so some combinations may cause undesired artifacts.
ordered
- the ordered dither specified by tr_orddith is performed
on the alpha channel.
This will only be used if the image has an alpha channel, and if there is space in the palette for a transparency color.
tr_threshold
- the highest alpha value at which a pixel will be
made transparent when transp
is 'threshold'. (0-255, default 127)
tr_errdiff
- The type of error diffusion to perform on the alpha
channel when transp
is errdiff
. This can be any defined error
diffusion type except for custom (see errdiff
below).
tr_orddith
- The type of ordered dither to perform on the alpha
channel when transp
is 'ordered'. Possible values are:
random
- A semi-random map is used. The map is the same each time.
dot8
- 8x8 dot dither.
dot4
- 4x4 dot dither
hline
- horizontal line dither.
vline
- vertical line dither.
/line
, slashline
- diagonal line dither
\line
, backline
- diagonal line dither
tiny
- dot matrix dither (currently the default). This is probably
the best for displays (like web pages).
custom
- A custom dither matrix is used - see tr_map
.
tr_map
- When tr_orddith is custom this defines an 8 x 8 matrix of
integers representing the transparency threshold for pixels
corresponding to each position. This should be a 64 element array
where the first 8 entries correspond to the first row of the matrix.
Values should be between 0 and 255.
make_colors
- Defines how the quantization engine will build the
palette(s). Currently this is ignored if translate
is giflib
,
but that may change. Possible values are:
none
- only colors supplied in 'colors' are used.
webmap
- the web color map is used (need URL here.)
addi
- The original code for generating the color map (Addi's code) is
used.
mediancut
- Uses a median-cut algorithm, faster than addi
, but not
as good a result.
mono
, monochrome
- a fixed black and white palette, suitable for
producing bi-level images (eg. facsimile)
gray
, gray4
, gray16
- make fixed gray palette with 256, 4 or
16 entries respectively.
Other methods may be added in the future.
colors
- an arrayref containing Imager::Color objects, which
represents the starting set of colors to use in translating the
images. webmap
will ignore this. On return the final colors used
are copied back into this array (which is expanded if necessary.)
max_colors
- the maximum number of colors to use in the image.
translate
- The method used to translate the RGB values in the
source image into the colors selected by make_colors. Note that
make_colors is ignored when translate
is giflib
.
Possible values are:
giflib
- this is a historical equivalent for closest
that also
forces make_colors
to mediancut
.
closest
- the closest color available is used.
perturb
- the pixel color is modified by perturb
, and the
closest color is chosen.
errdiff
- an error diffusion dither is performed. If the supplied
(or generated) palette contains only grays the source colors are
converted to gray before error diffusion is performed.
It's possible other translate
values will be added.
errdiff
- The type of error diffusion dither to perform. These
values (except for custom) can also be used in tr_errdif.
floyd
- Floyd-Steinberg dither
jarvis
- Jarvis, Judice and Ninke dither
stucki
- Stucki dither
custom
- custom. If you use this you must also set errdiff_width
,
errdiff_height
and errdiff_map
.
errdiff_width
, errdiff_height
, errdiff_orig
, errdiff_map
-
When translate
is errdiff
and errdiff
is custom
these
define a custom error diffusion map. errdiff_width
and
errdiff_height
define the size of the map in the arrayref in
errdiff_map
. errdiff_orig
is an integer which indicates the
current pixel position in the top row of the map.
perturb
- When translate is perturb
this is the magnitude of the
random bias applied to each channel of the pixel before it is looked
up in the color table.
This documents the Imager initialization function, which you will almost never need to call.
init()
This function is a mess, it can take the following named parameters:
log
- name of a log file to log Imager's actions to. Not all
actions are logged, but the debugging memory allocator does log
allocations here. Ignored if Imager has been built without logging
support. Preferably use the open_log()
method instead.
loglevel
- the maximum level of message to log. Default: 1.
warn_obsolete
- if this is non-zero then Imager will warn when you
attempt to use obsoleted parameters or functionality. This currently
only includes the old GIF output options instead of tags.
t1log
- if non-zero then T1lib will be configured to produce a log
file. This will fail if there are any existing T1lib font objects.
Example:
Imager::init(log => 'trace.log', loglevel => 9);
Imager can open an internal log to send debugging information to. This log is extensively used in Imager's tests, but you're unlikely to use it otherwise.
If Imager has been built with logging disabled, the methods fail quietly.
open_log()
log
- the file name to log to. If this is undef logging information
is sent to the standard error stream.
loglevel
the level of logging to produce. Default: 1.
Returns a true value if the log file was opened successfully.
# send debug output to test.log Imager->open_log(log => "test.log");
# send debug output to stderr Imager->open_log();
close_log()
No parameters.
Imager->close_log();
log()
Imager->log($message) Imager->log($message, $level)
This method does not use named parameters.
The default for $level
is 1.
Send a message to the debug log.
Imager->log("My code got here!");
is_logging()
Tony Cook <tonyc@cpan.org>, Arnar M. Hrafnkelsson
Imager(3), Imager::Files(3), Imager::Draw(3), Imager::Color(3), Imager::Fill(3), Imager::Font(3), Imager::Transformations(3), Imager::Engines(3), Imager::Filters(3), Imager::Expr(3), Imager::Matrix2d(3), Imager::Fountain(3)
Imager::ImageTypes - image models for Imager |