Provided by: libimager-perl_1.019+dfsg-1build2_amd64 
NAME
Imager::Transformations - Simple transformations of one image into another.
SYNOPSIS
use Imager;
$newimg = $img->copy();
$newimg = $img->scale(xpixels=>400, qtype => 'mixing');
$newimg = $img->scale(xpixels=>400, ypixels=>400);
$newimg = $img->scale(xpixels=>400, ypixels=>400, type=>'min');
$newimg = $img->scale(scalefactor=>0.25);
$newimg = $img->scaleX(pixels=>400);
$newimg = $img->scaleX(scalefactor=>0.25);
$newimg = $img->scaleY(pixels=>400);
$newimg = $img->scaleY(scalefactor=>0.25);
$newimg = $img->crop(left=>50, right=>100, top=>10, bottom=>100);
$newimg = $img->crop(left=>50, top=>10, width=>50, height=>90);
$dest->paste(left=>40,top=>20,img=>$logo);
$img->rubthrough(src=>$srcimage,tx=>30, ty=>50);
$img->rubthrough(src=>$srcimage,tx=>30, ty=>50,
src_minx=>20, src_miny=>30,
src_maxx=>20, src_maxy=>30);
$img->compose(src => $src, tx => 30, ty => 20, combine => 'color');
$img->compose(src => $src, tx => 30, ty => 20, combine => 'color');
mask => $mask, opacity => 0.5);
$img->flip(dir=>"h"); # horizontal flip
$img->flip(dir=>"vh"); # vertical and horizontal flip
$newimg = $img->copy->flip(dir=>"v"); # make a copy and flip it vertically
my $rot20 = $img->rotate(degrees=>20);
my $rotpi4 = $img->rotate(radians=>3.14159265/4);
# Convert image to gray
$new = $img->convert(preset=>'grey');
# Swap red/green channel
$new = $img->convert(matrix=>[ [ 0, 1, 0 ],
[ 1, 0, 0 ],
[ 0, 0, 1 ] ]);
# build an image using channels from multiple input images
$new = $img->combine(src => [ $im1, $im2, $im3 ]);
$new = $img->combine(src => [ $im1, $im2, $im3 ],
channels => [ 2, 1, 0 ]);
# limit the range of red channel from 0..255 to 0..127
@map = map { int( $_/2 } 0..255;
$img->map( red=>\@map );
# Apply a Gamma of 1.4
my $gamma = 1.4;
my @map = map { int( 0.5 + 255*($_/255)**$gamma ) } 0..255;
$img->map(all=>\@map); # inplace conversion
DESCRIPTION
The methods described in Imager::Transformations fall into two categories. Either they
take an existing image and modify it in place, or they return a modified copy.
Functions that modify inplace are "flip()", "paste()", "rubthrough()" and "compose()". If
the original is to be left intact it's possible to make a copy and alter the copy:
$flipped = $img->copy()->flip(dir=>'h');
Image copying/resizing/cropping/rotating
A list of the transformations that do not alter the source image follows:
copy()
To create a copy of an image use the "copy()" method. This is useful if you want to
keep an original after doing something that changes the image.
$newimg = $orig->copy();
scale()
To scale an image so proportions are maintained use the "$img->scale()" method. if
you give either a "xpixels" or "ypixels" parameter they will determine the width or
height respectively. If both are given the one resulting in a larger image is used,
unless you set the "type" parameter to 'min'. example: $img is 700 pixels wide and
500 pixels tall.
$newimg = $img->scale(xpixels=>400); # 400x285
$newimg = $img->scale(ypixels=>400); # 560x400
$newimg = $img->scale(xpixels=>400,ypixels=>400); # 560x400
$newimg = $img->scale(xpixels=>400,ypixels=>400,type=>'min'); # 400x285
$newimg = $img->scale(xpixels=>400, ypixels=>400),type=>'nonprop'); # 400x400
$newimg = $img->scale(scalefactor=>0.25); 175x125
$newimg = $img->scale(); # 350x250
If you want to create low quality previews of images you can pass "qtype=>'preview'"
to scale and it will use nearest neighbor sampling instead of filtering. It is much
faster but also generates worse looking images - especially if the original has a lot
of sharp variations and the scaled image is by more than 3-5 times smaller than the
original.
• "xpixels", "ypixels" - desired size of the scaled image. The "type" parameter
controls whether the larger or smaller of the two possible sizes is chosen, or if
the image is scaled non-proportionally.
• "constrain" - an Image::Math::Constrain object defining the way in which the image
size should be constrained.
• "scalefactor" - if none of "xpixels", "ypixels", "xscalefactor", "yscalefactor" or
"constrain" is supplied then this is used as the ratio to scale by. Default: 0.5.
• "xscalefactor", "yscalefactor" - if both are supplied then the image is scaled as
per these parameters, whether this is proportionally or not. New in Imager 0.54.
• "type" - controls whether the larger or smaller of the two possible sizes is
chosen, possible values are:
• "min" - the smaller of the 2 sizes are chosen.
• "max" - the larger of the 2 sizes. This is the default.
• "nonprop" - non-proportional scaling. New in Imager 0.54.
scale() will fail if "type" is set to some other value.
For example, if the original image is 400 pixels wide by 200 pixels high and
"xpixels" is set to 300, and "ypixels" is set to 160. When "type" is 'min' the
resulting image is 300 x 150, when "type" is 'max' the resulting image is 320 x
160.
"type" is only used if both "xpixels" and "ypixels" are supplied.
• "qtype" - defines the quality of scaling performed. Possible values are:
• "normal" - high quality scaling. This is the default.
• "preview" - lower quality. When scaling down this will skip input pixels, eg.
scaling by 0.5 will skip every other pixel. When scaling up this will
duplicate pixels.
• "mixing" - implements the mixing algorithm implemented by pnmscale. This
retains more detail when scaling down than "normal". When scaling down this
proportionally accumulates sample data from the pixels, resulting in a
proportional mix of all of the pixels. When scaling up this will mix pixels
when the sampling grid crosses a pixel boundary but will otherwise copy pixel
values.
scale() will fail if "qtype" is set to some other value.
"preview" is faster than "mixing" which is much faster than "normal".
To scale an image on a given axis without maintaining proportions, it is best to call
the scaleX() and scaleY() methods with the required dimensions. eg.
my $scaled = $img->scaleX(pixels=>400)->scaleY(pixels=>200);
From Imager 0.54 you can scale without maintaining proportions either by supplying
both the "xscalefactor" and "yscalefactor" arguments:
my $scaled = $img->scale(xscalefactor => 0.5, yscalefactor => 0.67);
or by supplying "xpixels" and "ypixels" and setting "type" to <nonprop>:
my $scaled = $im->scale(xpixels => 200, ypixels => 200, type => 'nonprop');
Returns a new scaled image on success. The source image is not modified.
Returns false on failure, check the errstr() method for the reason for failure.
A mandatory warning is produced if scale() is called in void context.
# setup
my $image = Imager->new;
$image->read(file => 'somefile.jpg')
or die $image->errstr;
# all full quality unless indicated otherwise
# half the size:
my $half = $image->scale;
# double the size
my $double = $image->scale(scalefactor => 2.0);
# so a 400 x 400 box fits in the resulting image:
my $fit400x400inside = $image->scale(xpixels => 400, ypixels => 400);
my $fit400x400inside2 = $image->scale(xpixels => 400, ypixels => 400,
type=>'max');
# fit inside a 400 x 400 box
my $inside400x400 = $image->scale(xpixels => 400, ypixels => 400,
type=>'min');
# make it 400 pixels wide or high
my $width400 = $image->scale(xpixels => 400);
my $height400 = $image->scale(ypixels => 400);
# low quality scales:
# to half size
my $low = $image->scale(qtype => 'preview');
# mixing method scale
my $mixed = $image->scale(qtype => 'mixing', scalefactor => 0.1);
# using an Image::Math::Constrain object
use Image::Math::Constrain;
my $constrain = Image::Math::Constrain->new(800, 600);
my $scaled = $image->scale(constrain => $constrain);
# same as Image::Math::Constrain version
my $scaled2 = $image->scale(xpixels => 800, ypixels => 600, type => 'min');
scaleX()
scaleX() will scale along the X dimension, return a new image with the new width:
my $newimg = $img->scaleX(pixels=>400); # 400x500
$newimg = $img->scaleX(scalefactor=>0.25) # 175x500
• "scalefactor" - the amount to scale the X axis. Ignored if "pixels" is provided.
Default: 0.5.
• "pixels" - the new width of the image.
Returns a new scaled image on success. The source image is not modified.
Returns false on failure, check the errstr() method for the reason for failure.
A mandatory warning is produced if scaleX() is called in void context.
scaleY()
scaleY() will scale along the Y dimension, return a new image with the new height:
$newimg = $img->scaleY(pixels=>400); # 700x400
$newimg = $img->scaleY(scalefactor=>0.25) # 700x125
• "scalefactor" - the amount to scale the Y axis. Ignored if "pixels" is provided.
Default: 0.5.
• "pixels" - the new height of the image.
Returns a new scaled image on success. The source image is not modified.
Returns false on failure, check the errstr() method for the reason for failure.
A mandatory warning is produced if scaleY() is called in void context.
scale_calculate()
Performs the same calculations that the scale() method does to calculate the scaling
factors from the parameters you pass.
scale_calculate() can be called as an object method, or as a class method.
Takes the following parameters over scale():
• "width", "height" - the image width and height to base the scaling on. Required
if scale_calculate() is called as a class method. If called as an object method
these default to the image width and height respectively.
You might use scale_calculate() as a class method when generating an HTML "IMG" tag,
for example.
Returns an empty list on failure.
Returns a list containing horizontal scale factor, vertical scale factor, new width,
new height, on success.
my ($x_scale, $y_scale, $new_width, $new_height) =
Imager->scale_calculate(width => 1024, height => 768,
ypixels => 180, type => 'min');
my ($x_scale, $y_scale, $new_width, $new_height) =
$img->scale_calculate(xpixels => 200, type => 'min');
crop()
Another way to resize an image is to crop it. The parameters to crop are the edges of
the area that you want in the returned image, where the right and bottom edges are
non-inclusive. If a parameter is omitted a default is used instead.
crop() returns the cropped image and does not modify the source image.
The possible parameters are:
• "left" - the left edge of the area to be cropped. Default: 0
• "top" - the top edge of the area to be cropped. Default: 0
• "right" - the right edge of the area to be cropped. Default: right edge of image.
• "bottom" - the bottom edge of the area to be cropped. Default: bottom edge of
image.
• "width" - width of the crop area. Ignored if both "left" and "right" are
supplied. Centered on the image if neither "left" nor "right" are supplied.
• "height" - height of the crop area. Ignored if both "top" and "bottom" are
supplied. Centered on the image if neither "top" nor "bottom" are supplied.
For example:
# these produce the same image
$newimg = $img->crop(left=>50, right=>100, top=>10, bottom=>100);
$newimg = $img->crop(left=>50, top=>10, width=>50, height=>90);
$newimg = $img->crop(right=>100, bottom=>100, width=>50, height=>90);
# and the following produce the same image
$newimg = $img->crop(left=>50, right=>100);
$newimg = $img->crop(left=>50, right=>100, top=>0,
bottom=>$img->getheight);
# grab the top left corner of the image
$newimg = $img->crop(right=>50, bottom=>50);
You can also specify width and height parameters which will produce a new image
cropped from the center of the input image, with the given width and height.
$newimg = $img->crop(width=>50, height=>50);
If you supply "left", "width" and "right" values, the "right" value will be ignored.
If you supply "top", "height" and "bottom" values, the "bottom" value will be ignored.
The edges of the cropped area default to the edges of the source image, for example:
# a vertical bar from the middle from top to bottom
$newimg = $img->crop(width=>50);
# the right half
$newimg = $img->crop(left=>$img->getwidth() / 2);
If the resulting image would have zero width or height then crop() returns false and
$img->errstr is an appropriate error message.
A mandatory warning is produced if crop() is called in void context.
rotate()
Use the rotate() method to rotate an image. This method will return a new, rotated
image.
To rotate by an exact amount in degrees or radians, use the 'degrees' or 'radians'
parameter:
my $rot20 = $img->rotate(degrees=>20);
my $rotpi4 = $img->rotate(radians=>3.14159265/4);
Exact image rotation uses the same underlying transformation engine as the
matrix_transform() method (see Imager::Engines).
You can also supply a "back" argument which acts as a background color for the areas
of the image with no samples available (outside the rectangle of the source image.)
This can be either an Imager::Color or Imager::Color::Float object. This is not mixed
transparent pixels in the middle of the source image, it is only used for pixels where
there is no corresponding pixel in the source image.
To rotate in steps of 90 degrees, use the 'right' parameter:
my $rotated = $img->rotate(right=>270);
Rotations are clockwise for positive values.
Parameters:
• "right" - rotate by an exact multiple of 90 degrees, specified in degrees.
• "radians" - rotate by an angle specified in radians.
• "degrees" - rotate by an angle specified in degrees.
• "back" - for "radians" and "degrees" this is the color used for the areas not
covered by the original image. For example, the corners of an image rotated by 45
degrees.
This can be either an Imager::Color object, an Imager::Color::Float object or any
parameter that Imager can convert to a color object, see "Color Parameters" in
Imager::Draw for details.
This is not mixed transparent pixels in the middle of the source image, it is only
used for pixels where there is no corresponding pixel in the source image.
Default: transparent black.
# rotate 45 degrees clockwise,
my $rotated = $img->rotate(degrees => 45);
# rotate 10 degrees counter-clockwise
# set pixels not sourced from the original to red
my $rotated = $img->rotate(degrees => -10, back => 'red');
trim()
Returns a cropped version of the original image cropped of border pixels based on
either transparent pixels, or pixels that match any of a set of provided colors.
If you just want the number of pixels to be cropped on each side you can use the
"trim_rect()" method.
If the supplied parameters would result in the entire image is cropped, then a single
pixel image is returned from the top left of the source image.
To trim just on fully transparent pixels:
my $trimmed = $img->trim();
To trim pixels with less than 1% coverage:
my $trimmed = $img->trim(alpha => 0.01);
To trim based on automatically determined colors and fully transparent pixels:
my $trimmed = $img->trim(auto => 1);
To trim a black border:
my $trimmed = $img->trim(colors => [ "#000" ]);
Parameters:
• "alpha" - any pixels with less than or equal coverage to this value will be
treated as part of the border to be cropped. This is always expressed as a
fraction, so "alpha =" 1.0> will treat all pixels as part of the border. Default:
0 (fully transparent pixels are part of the border).
• "auto" - automatically select colors to crop on. Possible values:
• 1 - a "best" mechanism is selected, this is currently the "center" method, but
it subject to change.
• "center", "centre" - the pixels at the center of each side of the image are
used.
• "tolerance" - used by the "auto" mechanism to control the range of pixel colors to
be accepted as part of the border. Default: 0.01.
• "colors" - either a Imager::TrimColorList object or a reference to an array of
color entries to be considered part of the border. Code like:
my $trimmed = $img->trim(colors => [ LIST ]);
results in a temporary Imager::TrimColorList being produced like:
my $trimmed = $img->trim(colors => Imager::TrimColorList->new( LIST ));
"colors" and "auto" exclude each other, only one or the other can be supplied.
trim_rect()
Returns a list of the number of columns and rows of that would be removed from each
side if trim() was called.
my ($left, $top, $right, $bottom) = $img->trim_rect();
If the entire image matches the trim parameters then $left will be the width of the
image and $top will be the height of the image.
Accepts the same parameters as "trim()".
Image pasting/flipping
A list of the transformations that alter the source image follows:
paste()
To copy an image to onto another image use the "paste()" method.
$dest->paste(left=>40, top=>20, src=>$logo);
That copies the entire $logo image onto the $dest image so that the upper left corner
of the $logo image is at (40,20).
Parameters:
• "src", "img" - the source image. "src" added for compatibility with rubthrough().
• "left", "top" - position in output of the top left of the pasted image. Default:
(0,0)
• "src_minx", "src_miny" - the top left corner in the source image to start the
paste from. Default: (0, 0)
• "src_maxx", "src_maxy" - the bottom right in the source image of the sub image to
paste. This position is non inclusive. Default: bottom right corner of the
source image.
• "width", "height" - if the corresponding src_maxx or src_maxy is not defined then
width or height is used for the width or height of the sub image to be pasted.
# copy the 20x20 pixel image from (20,20) in $src_image to (10,10) in $img
$img->paste(src=>$src_image,
left => 10, top => 10,
src_minx => 20, src_miny => 20,
src_maxx => 40, src_maxx => 40);
If the source image has an alpha channel and the target doesn't, then the source is
treated as if composed onto a black background.
If the source image is color and the target is gray scale, the source is treated as if
run through "convert(preset=>'gray')".
rubthrough()
A more complicated way of blending images is where one image is put 'over' the other
with a certain amount of opaqueness. The method that does this is rubthrough().
$img->rubthrough(src=>$overlay,
tx=>30, ty=>50,
src_minx=>20, src_miny=>30,
src_maxx=>20, src_maxy=>30);
That will take the sub image defined by $overlay and
[src_minx,src_maxx)[src_miny,src_maxy) and overlay it on top of $img with the upper
left corner at (30,50). You can rub 2 or 4 channel images onto a 3 channel image, or
a 2 channel image onto a 1 channel image. The last channel is used as an alpha
channel. To add an alpha channel to an image see convert().
Parameters:
• "tx", "ty" - location in the target image ($self) to render the top left corner of
the source.
• "src_minx", "src_miny" - the top left corner in the source to transfer to the
target image. Default: (0, 0).
• "src_maxx", "src_maxy" - the bottom right in the source image of the sub image to
overlay. This position is non inclusive. Default: bottom right corner of the
source image.
# overlay all of $source onto $targ
$targ->rubthrough(tx => 20, ty => 25, src => $source);
# overlay the top left corner of $source onto $targ
$targ->rubthrough(tx => 20, ty => 25, src => $source,
src_maxx => 20, src_maxy => 20);
# overlay the bottom right corner of $source onto $targ
$targ->rubthrough(tx => 20, ty => 30, src => $src,
src_minx => $src->getwidth() - 20,
src_miny => $src->getheight() - 20);
rubthrough() returns true on success. On failure check "$target->errstr" for the
reason for failure.
compose()
Draws the source image over the target image, with the source alpha channel modified
by the optional mask and the opacity.
$img->compose(src=>$overlay,
tx=>30, ty=>50,
src_minx=>20, src_miny=>30,
src_maxx=>20, src_maxy=>30,
mask => $mask, opacity => 0.5);
That will take the sub image defined by $overlay and
[src_minx,src_maxx)[src_miny,src_maxy) and overlay it on top of $img with the upper
left corner at (30,50). You can rub 2 or 4 channel images onto a 3 channel image, or
a 2 channel image onto a 1 channel image.
Parameters:
• "src" - the source image to draw onto the target. Required.
• "tx", "ty" - location in the target image ($self) to render the top left corner of
the source. These can also be supplied as "left" and "right". Default: (0, 0).
• "src_minx", "src_miny" - the top left corner in the source to transfer to the
target image. Default: (0, 0).
• "src_maxx", "src_maxy" - the bottom right in the source image of the sub image to
overlay. This position is non inclusive. Default: bottom right corner of the
source image.
• "mask" - a mask image. The first channel of this image is used to modify the
alpha channel of the source image. This can be used to mask out portions of the
source image. Where the first channel is zero none of the source image will be
used, where the first channel is maximum the full alpha of the source image will
be used, as further modified by the opacity.
• opacity - further modifies the alpha channel of the source image, in the range 0.0
to 1.0. Default: 1.0.
• combine - the method to combine the source pixels with the target. See the
combine option documentation in Imager::Fill. Default: normal.
Calling compose() with no mask, combine set to "normal", opacity set to 1.0 is
equivalent to calling rubthrough().
compose() is intended to be produce similar effects to layers in interactive paint
software.
# overlay all of $source onto $targ
$targ->compose(tx => 20, ty => 25, src => $source);
# overlay the top left corner of $source onto $targ
$targ->compose(tx => 20, ty => 25, src => $source,
src_maxx => 20, src_maxy => 20);
# overlay the bottom right corner of $source onto $targ
$targ->compose(tx => 20, ty => 30, src => $src,
src_minx => $src->getwidth() - 20,
src_miny => $src->getheight() - 20);
compose() returns true on success. On failure check $target->errstr for the reason
for failure.
flip()
An inplace horizontal or vertical flip is possible by calling the "flip()" method. If
the original is to be preserved it's possible to make a copy first. The only
parameter it takes is the "dir" parameter which can take the values "h", "v", "vh" and
"hv".
$img->flip(dir=>"h"); # horizontal flip
$img->flip(dir=>"vh"); # vertical and horizontal flip
$nimg = $img->copy->flip(dir=>"v"); # make a copy and flip it vertically
flip() returns true on success. On failure check $img->errstr for the reason for
failure.
Color transformations
convert()
You can use the convert method to transform the color space of an image using a
matrix. For ease of use some presets are provided.
The convert method can be used to:
• convert an RGB or RGBA image to gray scale.
• convert a gray scale image to RGB.
• extract a single channel from an image.
• set a given channel to a particular value (or from another channel)
The currently defined presets are:
• "gray", "grey" - converts an RGBA image into a gray scale image with alpha
channel, or an RGB image into a gray scale image without an alpha channel.
This weights the RGB channels at 22.2%, 70.7% and 7.1% respectively.
• "noalpha" - removes the alpha channel from a 2 or 4 channel image. An identity
for other images. Warning: this removes the alpha channel without applying it.
• "red", "channel0" - extracts the first channel of the image into a single channel
image
• "green", "channel1" - extracts the second channel of the image into a single
channel image
• "blue", "channel2" - extracts the third channel of the image into a single channel
image
• "alpha" - extracts the alpha channel of the image into a single channel image.
If the image has 1 or 3 channels (assumed to be gray scale or RGB) then the
resulting image will be all white.
• "rgb"
converts a gray scale image to RGB, preserving the alpha channel if any
• "addalpha" - adds an alpha channel to a gray scale or RGB image. Preserves an
existing alpha channel for a 2 or 4 channel image.
For example, to convert an RGB image into a gray scale image:
$new = $img->convert(preset=>'grey'); # or gray
or to convert a gray scale image to an RGB image:
$new = $img->convert(preset=>'rgb');
The presets aren't necessary simple constants in the code, some are generated based on
the number of channels in the input image.
If you want to perform some other color transformation, you can use the 'matrix'
parameter.
For each output pixel the following matrix multiplication is done:
| channel[0] | | $c00, ..., $c0k | | inchannel[0] |
| ... | = | ... | x | ... |
| channel[k] | | $ck0, ..., $ckk | | inchannel[k] |
1
Where C<k = $img-E<gt>getchannels()-1>.
So if you want to swap the red and green channels on a 3 channel image:
$new = $img->convert(matrix=>[ [ 0, 1, 0 ],
[ 1, 0, 0 ],
[ 0, 0, 1 ] ]);
or to convert a 3 channel image to gray scale using equal weightings:
$new = $img->convert(matrix=>[ [ 0.333, 0.333, 0.334 ] ])
Convert a 2 channel image (gray scale with alpha) to an RGBA image with the gray
converted to the specified RGB color:
# set (RGB) scaled on the grey scale portion and copy the alpha
# channel as is
my $colored = $gray->convert(matrix=>[ [ ($red/255), 0 ],
[ ($green/255), 0 ],
[ ($blue/255), 0 ],
[ 0, 1 ],
]);
To convert a 3 channel image to a 4 channel image with a 50 percent alpha channel:
my $withalpha = $rgb->convert(matrix =>[ [ 1, 0, 0, 0 ],
[ 0, 1, 0, 0 ],
[ 0, 0, 1, 0 ],
[ 0, 0, 0, 0.5 ],
]);
combine()
Combine channels from one or more input images into a new image.
Parameters:
• "src" - a reference to an array of input images. There must be at least one input
image. A given image may appear more than once in "src".
• "channels" - a reference to an array of channels corresponding to the source
images. If "channels" is not supplied then the first channel from each input
image is used. If the array referenced by "channels" is shorter than that
referenced by "src" then the first channel is used from the extra images.
# make an rgb image from red, green, and blue images
my $rgb = Imager->combine(src => [ $red, $green, $blue ]);
# convert a BGR image into RGB
my $rgb = Imager->combine(src => [ $bgr, $bgr, $bgr ],
channels => [ 2, 1, 0 ]);
# add an alpha channel from another image
my $rgba = Imager->combine(src => [ $rgb, $rgb, $rgb, $alpha ],
channels => [ 0, 1, 2, 0 ]);
Color Mappings
map()
You can use the map method to map the values of each channel of an image independently
using a list of look-up tables. It's important to realize that the modification is
made inplace. The function simply returns the input image again or undef on failure.
Each channel is mapped independently through a look-up table with 256 entries. The
elements in the table should not be less than 0 and not greater than 255. If they are
out of the 0..255 range they are clamped to the range. If a table does not contain
256 entries it is silently ignored.
Single channels can mapped by specifying their name and the mapping table. The
channel names are "red", "green", "blue", "alpha".
@map = map { int( $_/2 } 0..255;
$img->map( red=>\@map );
It is also possible to specify a single map that is applied to all channels, alpha
channel included. For example this applies a gamma correction with a gamma of 1.4 to
the input image.
$gamma = 1.4;
@map = map { int( 0.5 + 255*($_/255)**$gamma ) } 0..255;
$img->map(all=> \@map);
The "all" map is used as a default channel, if no other map is specified for a channel
then the "all" map is used instead. If we had not wanted to apply gamma to the alpha
channel we would have used:
$img->map(all=> \@map, alpha=>[]);
Since "[]" contains fewer than 256 element the gamma channel is unaffected.
It is also possible to simply specify an array of maps that are applied to the images
in the RGBA order. For example to apply maps to the "red" and "blue" channels one
would use:
$img->map(maps=>[\@redmap, [], \@bluemap]);
SEE ALSO
Imager, Imager::Engines
AUTHOR
Tony Cook <tonyc@cpan.org>, Arnar M. Hrafnkelsson
REVISION
$Revision$