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
$img->scale()
method. if you give either axpixels
orypixels
parameter they will determine the width or height respectively. If both are given the one resulting in a larger image is used, unless you set thetype
parameter to'min'
. example:$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. Thetype
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 ofxpixels
,ypixels
,xscalefactor
,yscalefactor
orconstrain
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
- when bothxpixels
andypixels
are supplied and do not scale the image proportionallytype
controls whether the larger or smaller of the two possible sizes is chosen, or whether the resulting image is stretched.Possible values are:
min
- the smaller of the two possible sizes is chosen.max
- the larger of the two possible sizes is chosen. This is the default.nonprop
- allow non-proportional scaling.
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, andypixels
is set to 160:# $image is 400x200 my $scaled = $image->scale(xpixels => 300, ypixels => 160, type => $type);
then scaling to 300x160 would distort the message, making it look stretched vertically.
Scaling to 300 x 150, based on
xpixels
or 320 x 160 based onypixels
prevents any stretching, preserving a ratio of two to one for width to height.When
type
ismin
the result is the smaller 300 x 150 image, whentype
ismax
the result is the larger 320 x 160 image.nonprop
doesn't attempt to scale proportionally at all, producing a 300 x 160 image.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 thannormal
. 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 thanmixing
which is much faster thannormal
.
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
andyscalefactor
arguments:my $scaled = $img->scale(xscalefactor => 0.5, yscalefactor => 0.67);
or by supplying
xpixels
andypixels
and settingtype
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 ifpixels
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 = $img->scaleY(scalefactor=>0.25) # 700x125
scalefactor
- the amount to scale the Y axis. Ignored ifpixels
is provided. Default: 0.5.pixels
- the new height of the image.
Returns a new scaled image on success. The source image is not modified.
Returns false on failure, check the errstr() method for the reason for failure.
A mandatory warning is produced if scaleY() is called in void context.
- scale_calculate()
-
Performs the same calculations that the scale() method does to calculate the scaling factors from the parameters you pass.
scale_calculate() can be called as an object method, or as a class method.
Takes the following parameters over scale():
width
,height
- the image width and height to base the scaling on. Required if scale_calculate() is called as a class method. If called as an object method these default to the image width and height respectively.
You might use scale_calculate() as a class method when generating an HTML
IMG
tag, for example.Returns an empty list on failure.
Returns a list containing horizontal scale factor, vertical scale factor, new width, new height, on success.
my ($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: 0top
- the top edge of the area to be cropped. Default: 0right
- 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 bothleft
andright
are supplied. Centered on the image if neitherleft
norright
are supplied.height
- height of the crop area. Ignored if bothtop
andbottom
are supplied. Centered on the image if neithertop
norbottom
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
andright
values, theright
value will be ignored. If you supplytop
,height
andbottom
values, thebottom
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
- forradians
anddegrees
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, soalpha =
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 thecenter
method, but it subject to change.center
,centre
- the pixels at the center of each side of the image are used.
tolerance
- used by theauto
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 = $img->trim(colors => Imager::TrimColorList->new( LIST ));
colors
andauto
exclude each other, only one or the other can be supplied. - trim_rect()
-
Returns a list of the number of columns and rows of that would be removed from each side if trim() was called.
my ($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 asleft
andright
. 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 to1.0
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 $target->errstr for the reason for failure.
- flip()
-
An inplace horizontal or vertical flip is possible by calling the
flip()
method. If the original is to be preserved it's possible to make a copy first. The only parameter it takes is thedir
parameter which can take the valuesh
,v
,vh
andhv
.$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)
add or remove extra channels to or from an image.
Parameters:
preset
- a preset conversion as listed below.matrix
- a reference to an array containing references to arrays of coefficients as documented below used to specify non-extra channels for the image. Either this orpreset
is required.extra
- a reference to an array containing references to arrays of coefficients as documented below used to specify extra channels for the image. Defaults to not add (or even keeping) extra channels from the source image.scale
- whether the linear luminance of each channel is used, or the numeric value. Possible values are "linear" or "gamma". Default: "linear".
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 imagegreen
,channel1
- extracts the second channel of the image into a single channel imageblue
,channel2
- extracts the third channel of the image into a single channel imagealpha
- 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 ], ]);
To add an extra channel all set to 255 to a 3 channel input image:
my $withextra = $rgb->convert(matrix => [ [ 1, 0, 0 ], [ 0, 1, 0 ], [ 0, 0, 1 ] ], extra => [ [ 0, 0, 0, 1 ] ]);
- 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 insrc
.channels
- a reference to an array of channels corresponding to the source images. Ifchannels
is not supplied then the first channel from each input image is used. If the array referenced bychannels
is shorter than that referenced bysrc
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; $img->map(all=> \@map);
The
all
map is used as a default channel, if no other map is specified for a channel then theall
map is used instead. If we had not wanted to apply gamma to the alpha channel we would have used:$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
andblue
channels one would use:$img->map(maps=>[\@redmap, [], \@bluemap]);
SEE ALSO
AUTHOR
Tony Cook <tonyc@cpan.org>, Arnar M. Hrafnkelsson
REVISION
$Revision$