/ 
Imager-0.45_02
River stage three • 112 direct dependents • 130 total dependents
/ Imager::Transformations

NAME

Imager::Transformations - Simple transformations of one image into another.

SYNOPSIS

use Imager;

$newimg = $img->copy();

$newimg = $img->scale(xpixels=>400);
$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->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 ] ]);

# 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() and rubthrough(). 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 usefull if you want to keep an original after doing something that changes the image.

$newimg = $orig->copy();
scale
scaleX
scaleY

To scale an image so porportions 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(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.

If you need to scale images per axis it is best to do it simply by calling scaleX() or scaleY(). You can pass either 'scalefactor' or 'pixels' to both functions.

scaleX() will scale along the X dimension, changing the width of the image:

$newimg = $img->scaleX(pixels=>400); # 400x500
$newimg = $img->scaleX(scalefactor=>0.25) # 175x500

scaleY() will scale along the Y dimension, changing the height of the image:

$newimg = $img->scaleY(pixels=>400); # 700x400
$newimg = $img->scaleY(scalefactor=>0.25) # 700x125
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.

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.

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.

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.

$dest->paste(left=>40,top=>20,img=>$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).

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().

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

Color transformations

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 grayscale.

  • convert a grayscale 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 grayscale image with alpha channel, or an RGB image into a grayscale 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.

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 grayscale of RGB) then the resulting image will be all white.

rgb

converts a grayscale image to RGB, preserving the alpha channel if any

addalpha

adds an alpha channel to a grayscale or RGB image. Preserves an existing alpha channel for a 2 or 4 channel image.

For example, to convert an RGB image into a greyscale image:

$new = $img->convert(preset=>'grey'); # or gray

or to convert a grayscale 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 colour 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 greyscale using equal weightings:

$new = $img->convert(matrix=>[ [ 0.333, 0.333, 0.334 ] ])

Convert a 2 channel image (grayscale with alpha) to an RGBA image with the grey 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 ],
                                     ]);

Color Mappings

You can use the map method to map the values of each channel of an image independently using a list of lookup 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 lookup 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]);