1Imager::TransformationsU(s3e)r Contributed Perl DocumentaItmiaogner::Transformations(3)
2
6 Imager::Transformations - Simple transformations of one image into
7 another.
8
10 use Imager;
11 $newimg = $img->copy();
13 $newimg = $img->scale(xpixels=>400, qtype => 'mixing');
15 $newimg = $img->scale(xpixels=>400, ypixels=>400);
16 $newimg = $img->scale(xpixels=>400, ypixels=>400, type=>'min');
17 $newimg = $img->scale(scalefactor=>0.25);
18 $newimg = $img->scaleX(pixels=>400);
20 $newimg = $img->scaleX(scalefactor=>0.25);
21 $newimg = $img->scaleY(pixels=>400);
22 $newimg = $img->scaleY(scalefactor=>0.25);
23 $newimg = $img->crop(left=>50, right=>100, top=>10, bottom=>100);
25 $newimg = $img->crop(left=>50, top=>10, width=>50, height=>90);
26 $dest->paste(left=>40,top=>20,img=>$logo);
28 $img->rubthrough(src=>$srcimage,tx=>30, ty=>50);
30 $img->rubthrough(src=>$srcimage,tx=>30, ty=>50,
31 src_minx=>20, src_miny=>30,
32 src_maxx=>20, src_maxy=>30);
33 $img->compose(src => $src, tx => 30, ty => 20, combine => 'color');
35 $img->compose(src => $src, tx => 30, ty => 20, combine => 'color');
36 mask => $mask, opacity => 0.5);
37 $img->flip(dir=>"h"); # horizontal flip
39 $img->flip(dir=>"vh"); # vertical and horizontal flip
40 $newimg = $img->copy->flip(dir=>"v"); # make a copy and flip it vertically
41 my $rot20 = $img->rotate(degrees=>20);
43 my $rotpi4 = $img->rotate(radians=>3.14159265/4);
44 # Convert image to gray
47 $new = $img->convert(preset=>'grey');
48 # Swap red/green channel
50 $new = $img->convert(matrix=>[ [ 0, 1, 0 ],
51 [ 1, 0, 0 ],
52 [ 0, 0, 1 ] ]);
53 # build an image using channels from multiple input images
55 $new = $img->combine(src => [ $im1, $im2, $im3 ]);
56 $new = $img->combine(src => [ $im1, $im2, $im3 ],
57 channels => [ 2, 1, 0 ]);
58 # limit the range of red channel from 0..255 to 0..127
60 @map = map { int( $_/2 } 0..255;
61 $img->map( red=>\@map );
62 # Apply a Gamma of 1.4
64 my $gamma = 1.4;
65 my @map = map { int( 0.5 + 255*($_/255)**$gamma ) } 0..255;
66 $img->map(all=>\@map); # inplace conversion
67
69 The methods described in Imager::Transformations fall into two
70 categories. Either they take an existing image and modify it in place,
71 or they return a modified copy.
72 Functions that modify inplace are "flip()", "paste()", "rubthrough()"
74 and "compose()". If the original is to be left intact it's possible to
75 make a copy and alter the copy:
76 $flipped = $img->copy()->flip(dir=>'h');
78 Image copying/resizing/cropping/rotating
80 A list of the transformations that do not alter the source image
81 follows:
82 copy()
84 To create a copy of an image use the "copy()" method. This is
85 useful if you want to keep an original after doing something that
86 changes the image.
87 $newimg = $orig->copy();
89 scale()
91 To scale an image so proportions are maintained use the
92 "$img->scale()" method. if you give either a "xpixels" or
93 "ypixels" parameter they will determine the width or height
94 respectively. If both are given the one resulting in a larger
95 image is used, unless you set the "type" parameter to 'min'.
96 example: $img is 700 pixels wide and 500 pixels tall.
97 $newimg = $img->scale(xpixels=>400); # 400x285
99 $newimg = $img->scale(ypixels=>400); # 560x400
100 $newimg = $img->scale(xpixels=>400,ypixels=>400); # 560x400
102 $newimg = $img->scale(xpixels=>400,ypixels=>400,type=>'min'); # 400x285
103 $newimg = $img->scale(xpixels=>400, ypixels=>400),type=>'nonprop'); # 400x400
105 $newimg = $img->scale(scalefactor=>0.25); 175x125
107 $newimg = $img->scale(); # 350x250
108 If you want to create low quality previews of images you can pass
110 "qtype=>'preview'" to scale and it will use nearest neighbor
111 sampling instead of filtering. It is much faster but also generates
112 worse looking images - especially if the original has a lot of
113 sharp variations and the scaled image is by more than 3-5 times
114 smaller than the original.
115 • "xpixels", "ypixels" - desired size of the scaled image. The
117 "type" parameter controls whether the larger or smaller of the
118 two possible sizes is chosen, or if the image is scaled non-
119 proportionally.
120 • "constrain" - an Image::Math::Constrain object defining the way
122 in which the image size should be constrained.
123 • "scalefactor" - if none of "xpixels", "ypixels",
125 "xscalefactor", "yscalefactor" or "constrain" is supplied then
126 this is used as the ratio to scale by. Default: 0.5.
127 • "xscalefactor", "yscalefactor" - if both are supplied then the
129 image is scaled as per these parameters, whether this is
130 proportionally or not. New in Imager 0.54.
131 • "type" - controls whether the larger or smaller of the two
133 possible sizes is chosen, possible values are:
134 • "min" - the smaller of the 2 sizes are chosen.
136 • "max" - the larger of the 2 sizes. This is the default.
138 • "nonprop" - non-proportional scaling. New in Imager 0.54.
140 scale() will fail if "type" is set to some other value.
142 For example, if the original image is 400 pixels wide by 200
144 pixels high and "xpixels" is set to 300, and "ypixels" is set
145 to 160. When "type" is 'min' the resulting image is 300 x 150,
146 when "type" is 'max' the resulting image is 320 x 160.
147 "type" is only used if both "xpixels" and "ypixels" are
149 supplied.
150 • "qtype" - defines the quality of scaling performed. Possible
152 values are:
153 • "normal" - high quality scaling. This is the default.
155 • "preview" - lower quality. When scaling down this will
157 skip input pixels, eg. scaling by 0.5 will skip every other
158 pixel. When scaling up this will duplicate pixels.
159 • "mixing" - implements the mixing algorithm implemented by
161 pnmscale. This retains more detail when scaling down than
162 "normal". When scaling down this proportionally
163 accumulates sample data from the pixels, resulting in a
164 proportional mix of all of the pixels. When scaling up
165 this will mix pixels when the sampling grid crosses a pixel
166 boundary but will otherwise copy pixel values.
167 scale() will fail if "qtype" is set to some other value.
169 "preview" is faster than "mixing" which is much faster than
171 "normal".
172 To scale an image on a given axis without maintaining proportions,
174 it is best to call the scaleX() and scaleY() methods with the
175 required dimensions. eg.
176 my $scaled = $img->scaleX(pixels=>400)->scaleY(pixels=>200);
178 From Imager 0.54 you can scale without maintaining proportions
180 either by supplying both the "xscalefactor" and "yscalefactor"
181 arguments:
182 my $scaled = $img->scale(xscalefactor => 0.5, yscalefactor => 0.67);
184 or by supplying "xpixels" and "ypixels" and setting "type" to
186 <nonprop>:
187 my $scaled = $im->scale(xpixels => 200, ypixels => 200, type => 'nonprop');
189 Returns a new scaled image on success. The source image is not
191 modified.
192 Returns false on failure, check the errstr() method for the reason
194 for failure.
195 A mandatory warning is produced if scale() is called in void
197 context.
198 # setup
200 my $image = Imager->new;
201 $image->read(file => 'somefile.jpg')
202 or die $image->errstr;
203 # all full quality unless indicated otherwise
205 # half the size:
206 my $half = $image->scale;
207 # double the size
209 my $double = $image->scale(scalefactor => 2.0);
210 # so a 400 x 400 box fits in the resulting image:
212 my $fit400x400inside = $image->scale(xpixels => 400, ypixels => 400);
213 my $fit400x400inside2 = $image->scale(xpixels => 400, ypixels => 400,
214 type=>'max');
215 # fit inside a 400 x 400 box
217 my $inside400x400 = $image->scale(xpixels => 400, ypixels => 400,
218 type=>'min');
219 # make it 400 pixels wide or high
221 my $width400 = $image->scale(xpixels => 400);
222 my $height400 = $image->scale(ypixels => 400);
223 # low quality scales:
225 # to half size
226 my $low = $image->scale(qtype => 'preview');
227 # mixing method scale
229 my $mixed = $image->scale(qtype => 'mixing', scalefactor => 0.1);
230 # using an Image::Math::Constrain object
232 use Image::Math::Constrain;
233 my $constrain = Image::Math::Constrain->new(800, 600);
234 my $scaled = $image->scale(constrain => $constrain);
235 # same as Image::Math::Constrain version
237 my $scaled2 = $image->scale(xpixels => 800, ypixels => 600, type => 'min');
238 scaleX()
240 scaleX() will scale along the X dimension, return a new image with
241 the new width:
242 my $newimg = $img->scaleX(pixels=>400); # 400x500
244 $newimg = $img->scaleX(scalefactor=>0.25) # 175x500
245 • "scalefactor" - the amount to scale the X axis. Ignored if
247 "pixels" is provided. Default: 0.5.
248 • "pixels" - the new width of the image.
250 Returns a new scaled image on success. The source image is not
252 modified.
253 Returns false on failure, check the errstr() method for the reason
255 for failure.
256 A mandatory warning is produced if scaleX() is called in void
258 context.
259 scaleY()
261 scaleY() will scale along the Y dimension, return a new image with
262 the new height:
263 $newimg = $img->scaleY(pixels=>400); # 700x400
265 $newimg = $img->scaleY(scalefactor=>0.25) # 700x125
266 • "scalefactor" - the amount to scale the Y axis. Ignored if
268 "pixels" is provided. Default: 0.5.
269 • "pixels" - the new height of the image.
271 Returns a new scaled image on success. The source image is not
273 modified.
274 Returns false on failure, check the errstr() method for the reason
276 for failure.
277 A mandatory warning is produced if scaleY() is called in void
279 context.
280 scale_calculate()
282 Performs the same calculations that the scale() method does to
283 calculate the scaling factors from the parameters you pass.
284 scale_calculate() can be called as an object method, or as a class
286 method.
287 Takes the following parameters over scale():
289 • "width", "height" - the image width and height to base the
291 scaling on. Required if scale_calculate() is called as a class
292 method. If called as an object method these default to the
293 image width and height respectively.
294 You might use scale_calculate() as a class method when generating
296 an HTML "IMG" tag, for example.
297 Returns an empty list on failure.
299 Returns a list containing horizontal scale factor, vertical scale
301 factor, new width, new height, on success.
302 my ($x_scale, $y_scale, $new_width, $new_height) =
304 Imager->scale_calculate(width => 1024, height => 768,
305 ypixels => 180, type => 'min');
306 my ($x_scale, $y_scale, $new_width, $new_height) =
308 $img->scale_calculate(xpixels => 200, type => 'min');
309 crop()
311 Another way to resize an image is to crop it. The parameters to
312 crop are the edges of the area that you want in the returned image,
313 where the right and bottom edges are non-inclusive. If a parameter
314 is omitted a default is used instead.
315 crop() returns the cropped image and does not modify the source
317 image.
318 The possible parameters are:
320 • "left" - the left edge of the area to be cropped. Default: 0
322 • "top" - the top edge of the area to be cropped. Default: 0
324 • "right" - the right edge of the area to be cropped. Default:
326 right edge of image.
327 • "bottom" - the bottom edge of the area to be cropped. Default:
329 bottom edge of image.
330 • "width" - width of the crop area. Ignored if both "left" and
332 "right" are supplied. Centered on the image if neither "left"
333 nor "right" are supplied.
334 • "height" - height of the crop area. Ignored if both "top" and
336 "bottom" are supplied. Centered on the image if neither "top"
337 nor "bottom" are supplied.
338 For example:
340 # these produce the same image
342 $newimg = $img->crop(left=>50, right=>100, top=>10, bottom=>100);
343 $newimg = $img->crop(left=>50, top=>10, width=>50, height=>90);
344 $newimg = $img->crop(right=>100, bottom=>100, width=>50, height=>90);
345 # and the following produce the same image
347 $newimg = $img->crop(left=>50, right=>100);
348 $newimg = $img->crop(left=>50, right=>100, top=>0,
349 bottom=>$img->getheight);
350 # grab the top left corner of the image
352 $newimg = $img->crop(right=>50, bottom=>50);
353 You can also specify width and height parameters which will produce
355 a new image cropped from the center of the input image, with the
356 given width and height.
357 $newimg = $img->crop(width=>50, height=>50);
359 If you supply "left", "width" and "right" values, the "right" value
361 will be ignored. If you supply "top", "height" and "bottom"
362 values, the "bottom" value will be ignored.
363 The edges of the cropped area default to the edges of the source
365 image, for example:
366 # a vertical bar from the middle from top to bottom
368 $newimg = $img->crop(width=>50);
369 # the right half
371 $newimg = $img->crop(left=>$img->getwidth() / 2);
372 If the resulting image would have zero width or height then crop()
374 returns false and $img->errstr is an appropriate error message.
375 A mandatory warning is produced if crop() is called in void
377 context.
378 rotate()
380 Use the rotate() method to rotate an image. This method will
381 return a new, rotated image.
382 To rotate by an exact amount in degrees or radians, use the
384 'degrees' or 'radians' parameter:
385 my $rot20 = $img->rotate(degrees=>20);
387 my $rotpi4 = $img->rotate(radians=>3.14159265/4);
388 Exact image rotation uses the same underlying transformation engine
390 as the matrix_transform() method (see Imager::Engines).
391 You can also supply a "back" argument which acts as a background
393 color for the areas of the image with no samples available (outside
394 the rectangle of the source image.) This can be either an
395 Imager::Color or Imager::Color::Float object. This is not mixed
396 transparent pixels in the middle of the source image, it is only
397 used for pixels where there is no corresponding pixel in the source
398 image.
399 To rotate in steps of 90 degrees, use the 'right' parameter:
401 my $rotated = $img->rotate(right=>270);
403 Rotations are clockwise for positive values.
405 Parameters:
407 • "right" - rotate by an exact multiple of 90 degrees, specified
409 in degrees.
410 • "radians" - rotate by an angle specified in radians.
412 • "degrees" - rotate by an angle specified in degrees.
414 • "back" - for "radians" and "degrees" this is the color used for
416 the areas not covered by the original image. For example, the
417 corners of an image rotated by 45 degrees.
418 This can be either an Imager::Color object, an
420 Imager::Color::Float object or any parameter that Imager can
421 convert to a color object, see "Color Parameters" in
422 Imager::Draw for details.
423 This is not mixed transparent pixels in the middle of the
425 source image, it is only used for pixels where there is no
426 corresponding pixel in the source image.
427 Default: transparent black.
429 # rotate 45 degrees clockwise,
431 my $rotated = $img->rotate(degrees => 45);
432 # rotate 10 degrees counter-clockwise
434 # set pixels not sourced from the original to red
435 my $rotated = $img->rotate(degrees => -10, back => 'red');
436 Image pasting/flipping
438 A list of the transformations that alter the source image follows:
439 paste()
441 To copy an image to onto another image use the "paste()" method.
442 $dest->paste(left=>40, top=>20, src=>$logo);
444 That copies the entire $logo image onto the $dest image so that the
446 upper left corner of the $logo image is at (40,20).
447 Parameters:
449 • "src", "img" - the source image. "src" added for compatibility
451 with rubthrough().
452 • "left", "top" - position in output of the top left of the
454 pasted image. Default: (0,0)
455 • "src_minx", "src_miny" - the top left corner in the source
457 image to start the paste from. Default: (0, 0)
458 • "src_maxx", "src_maxy" - the bottom right in the source image
460 of the sub image to paste. This position is non inclusive.
461 Default: bottom right corner of the source image.
462 • "width", "height" - if the corresponding src_maxx or src_maxy
464 is not defined then width or height is used for the width or
465 height of the sub image to be pasted.
466 # copy the 20x20 pixel image from (20,20) in $src_image to (10,10) in $img
468 $img->paste(src=>$src_image,
469 left => 10, top => 10,
470 src_minx => 20, src_miny => 20,
471 src_maxx => 40, src_maxx => 40);
472 If the source image has an alpha channel and the target doesn't,
474 then the source is treated as if composed onto a black background.
475 If the source image is color and the target is gray scale, the
477 source is treated as if run through "convert(preset=>'gray')".
478 rubthrough()
480 A more complicated way of blending images is where one image is put
481 'over' the other with a certain amount of opaqueness. The method
482 that does this is rubthrough().
483 $img->rubthrough(src=>$overlay,
485 tx=>30, ty=>50,
486 src_minx=>20, src_miny=>30,
487 src_maxx=>20, src_maxy=>30);
488 That will take the sub image defined by $overlay and
490 [src_minx,src_maxx)[src_miny,src_maxy) and overlay it on top of
491 $img with the upper left corner at (30,50). You can rub 2 or 4
492 channel images onto a 3 channel image, or a 2 channel image onto a
493 1 channel image. The last channel is used as an alpha channel. To
494 add an alpha channel to an image see convert().
495 Parameters:
497 • "tx", "ty" - location in the target image ($self) to render the
499 top left corner of the source.
500 • "src_minx", "src_miny" - the top left corner in the source to
502 transfer to the target image. Default: (0, 0).
503 • "src_maxx", "src_maxy" - the bottom right in the source image
505 of the sub image to overlay. This position is non inclusive.
506 Default: bottom right corner of the source image.
507 # overlay all of $source onto $targ
509 $targ->rubthrough(tx => 20, ty => 25, src => $source);
510 # overlay the top left corner of $source onto $targ
512 $targ->rubthrough(tx => 20, ty => 25, src => $source,
513 src_maxx => 20, src_maxy => 20);
514 # overlay the bottom right corner of $source onto $targ
516 $targ->rubthrough(tx => 20, ty => 30, src => $src,
517 src_minx => $src->getwidth() - 20,
518 src_miny => $src->getheight() - 20);
519 rubthrough() returns true on success. On failure check
521 "$target->errstr" for the reason for failure.
522 compose()
524 Draws the source image over the target image, with the source alpha
525 channel modified by the optional mask and the opacity.
526 $img->compose(src=>$overlay,
528 tx=>30, ty=>50,
529 src_minx=>20, src_miny=>30,
530 src_maxx=>20, src_maxy=>30,
531 mask => $mask, opacity => 0.5);
532 That will take the sub image defined by $overlay and
534 [src_minx,src_maxx)[src_miny,src_maxy) and overlay it on top of
535 $img with the upper left corner at (30,50). You can rub 2 or 4
536 channel images onto a 3 channel image, or a 2 channel image onto a
537 1 channel image.
538 Parameters:
540 • "src" - the source image to draw onto the target. Required.
542 • "tx", "ty" - location in the target image ($self) to render the
544 top left corner of the source. These can also be supplied as
545 "left" and "right". Default: (0, 0).
546 • "src_minx", "src_miny" - the top left corner in the source to
548 transfer to the target image. Default: (0, 0).
549 • "src_maxx", "src_maxy" - the bottom right in the source image
551 of the sub image to overlay. This position is non inclusive.
552 Default: bottom right corner of the source image.
553 • "mask" - a mask image. The first channel of this image is used
555 to modify the alpha channel of the source image. This can be
556 used to mask out portions of the source image. Where the first
557 channel is zero none of the source image will be used, where
558 the first channel is maximum the full alpha of the source image
559 will be used, as further modified by the opacity.
560 • opacity - further modifies the alpha channel of the source
562 image, in the range 0.0 to 1.0. Default: 1.0.
563 • combine - the method to combine the source pixels with the
565 target. See the combine option documentation in Imager::Fill.
566 Default: normal.
567 Calling compose() with no mask, combine set to "normal", opacity
569 set to 1.0 is equivalent to calling rubthrough().
570 compose() is intended to be produce similar effects to layers in
572 interactive paint software.
573 # overlay all of $source onto $targ
575 $targ->compose(tx => 20, ty => 25, src => $source);
576 # overlay the top left corner of $source onto $targ
578 $targ->compose(tx => 20, ty => 25, src => $source,
579 src_maxx => 20, src_maxy => 20);
580 # overlay the bottom right corner of $source onto $targ
582 $targ->compose(tx => 20, ty => 30, src => $src,
583 src_minx => $src->getwidth() - 20,
584 src_miny => $src->getheight() - 20);
585 compose() returns true on success. On failure check
587 $target->errstr for the reason for failure.
588 flip()
590 An inplace horizontal or vertical flip is possible by calling the
591 "flip()" method. If the original is to be preserved it's possible
592 to make a copy first. The only parameter it takes is the "dir"
593 parameter which can take the values "h", "v", "vh" and "hv".
594 $img->flip(dir=>"h"); # horizontal flip
596 $img->flip(dir=>"vh"); # vertical and horizontal flip
597 $nimg = $img->copy->flip(dir=>"v"); # make a copy and flip it vertically
598 flip() returns true on success. On failure check $img->errstr for
600 the reason for failure.
601 Color transformations
603 convert()
604 You can use the convert method to transform the color space of an
605 image using a matrix. For ease of use some presets are provided.
606 The convert method can be used to:
608 • convert an RGB or RGBA image to gray scale.
610 • convert a gray scale image to RGB.
612 • extract a single channel from an image.
614 • set a given channel to a particular value (or from another
616 channel)
617 The currently defined presets are:
619 • "gray", "grey" - converts an RGBA image into a gray scale image
621 with alpha channel, or an RGB image into a gray scale image
622 without an alpha channel.
623 This weights the RGB channels at 22.2%, 70.7% and 7.1%
625 respectively.
626 • "noalpha" - removes the alpha channel from a 2 or 4 channel
628 image. An identity for other images. Warning: this removes
629 the alpha channel without applying it.
630 • "red", "channel0" - extracts the first channel of the image
632 into a single channel image
633 • "green", "channel1" - extracts the second channel of the image
635 into a single channel image
636 • "blue", "channel2" - extracts the third channel of the image
638 into a single channel image
639 • "alpha" - extracts the alpha channel of the image into a single
641 channel image.
642 If the image has 1 or 3 channels (assumed to be gray scale or
644 RGB) then the resulting image will be all white.
645 • "rgb"
647 converts a gray scale image to RGB, preserving the alpha
649 channel if any
650 • "addalpha" - adds an alpha channel to a gray scale or RGB
652 image. Preserves an existing alpha channel for a 2 or 4
653 channel image.
654 For example, to convert an RGB image into a gray scale image:
656 $new = $img->convert(preset=>'grey'); # or gray
658 or to convert a gray scale image to an RGB image:
660 $new = $img->convert(preset=>'rgb');
662 The presets aren't necessary simple constants in the code, some are
664 generated based on the number of channels in the input image.
665 If you want to perform some other color transformation, you can use
667 the 'matrix' parameter.
668 For each output pixel the following matrix multiplication is done:
670 | channel[0] | | $c00, ..., $c0k | | inchannel[0] |
672 | ... | = | ... | x | ... |
673 | channel[k] | | $ck0, ..., $ckk | | inchannel[k] |
674 1
675 Where C<k = $img-E<gt>getchannels()-1>.
676 So if you want to swap the red and green channels on a 3 channel
678 image:
679 $new = $img->convert(matrix=>[ [ 0, 1, 0 ],
681 [ 1, 0, 0 ],
682 [ 0, 0, 1 ] ]);
683 or to convert a 3 channel image to gray scale using equal
685 weightings:
686 $new = $img->convert(matrix=>[ [ 0.333, 0.333, 0.334 ] ])
688 Convert a 2 channel image (gray scale with alpha) to an RGBA image
690 with the gray converted to the specified RGB color:
691 # set (RGB) scaled on the grey scale portion and copy the alpha
693 # channel as is
694 my $colored = $gray->convert(matrix=>[ [ ($red/255), 0 ],
695 [ ($green/255), 0 ],
696 [ ($blue/255), 0 ],
697 [ 0, 1 ],
698 ]);
699 To convert a 3 channel image to a 4 channel image with a 50 percent
701 alpha channel:
702 my $withalpha = $rgb->convert(matrix =>[ [ 1, 0, 0, 0 ],
704 [ 0, 1, 0, 0 ],
705 [ 0, 0, 1, 0 ],
706 [ 0, 0, 0, 0.5 ],
707 ]);
708 combine()
710 Combine channels from one or more input images into a new image.
711 Parameters:
713 • "src" - a reference to an array of input images. There must be
715 at least one input image. A given image may appear more than
716 once in "src".
717 • "channels" - a reference to an array of channels corresponding
719 to the source images. If "channels" is not supplied then the
720 first channel from each input image is used. If the array
721 referenced by "channels" is shorter than that referenced by
722 "src" then the first channel is used from the extra images.
723 # make an rgb image from red, green, and blue images
725 my $rgb = Imager->combine(src => [ $red, $green, $blue ]);
726 # convert a BGR image into RGB
728 my $rgb = Imager->combine(src => [ $bgr, $bgr, $bgr ],
729 channels => [ 2, 1, 0 ]);
730 # add an alpha channel from another image
732 my $rgba = Imager->combine(src => [ $rgb, $rgb, $rgb, $alpha ],
733 channels => [ 0, 1, 2, 0 ]);
734 Color Mappings
736 map()
737 You can use the map method to map the values of each channel of an
738 image independently using a list of look-up tables. It's important
739 to realize that the modification is made inplace. The function
740 simply returns the input image again or undef on failure.
741 Each channel is mapped independently through a look-up table with
743 256 entries. The elements in the table should not be less than 0
744 and not greater than 255. If they are out of the 0..255 range they
745 are clamped to the range. If a table does not contain 256 entries
746 it is silently ignored.
747 Single channels can mapped by specifying their name and the mapping
749 table. The channel names are "red", "green", "blue", "alpha".
750 @map = map { int( $_/2 } 0..255;
752 $img->map( red=>\@map );
753 It is also possible to specify a single map that is applied to all
755 channels, alpha channel included. For example this applies a gamma
756 correction with a gamma of 1.4 to the input image.
757 $gamma = 1.4;
759 @map = map { int( 0.5 + 255*($_/255)**$gamma ) } 0..255;
760 $img->map(all=> \@map);
761 The "all" map is used as a default channel, if no other map is
763 specified for a channel then the "all" map is used instead. If we
764 had not wanted to apply gamma to the alpha channel we would have
765 used:
766 $img->map(all=> \@map, alpha=>[]);
768 Since "[]" contains fewer than 256 element the gamma channel is
770 unaffected.
771 It is also possible to simply specify an array of maps that are
773 applied to the images in the RGBA order. For example to apply maps
774 to the "red" and "blue" channels one would use:
775 $img->map(maps=>[\@redmap, [], \@bluemap]);
777
779 Imager, Imager::Engines
780
782 Tony Cook <tonyc@cpan.org>, Arnar M. Hrafnkelsson
783
785 $Revision$
786perl v5.34.0 2021-07-22 Imager::Transformations(3)