Gimp::Pixel - how to operate on raw pixels
use Gimp; # all you need is in Gimp. # Gimp::GDrawable - The GDrawable structure # Gimp::Tile - The Tile family of functions. # Gimp::PixelRgn - The PixelRgn family of functions.
You can access the pixels in a drawable through tiles or pixel regions. This manpage explains how this is done in perl. All classes (Gimp::GDrawable, Gimp::Tile, Gimp::PixelRgn) are available with and without the Gimp:: prefix.
Gimp::
Well, you know drawables? (also known as PARAM_DRAWABLE or Gimp::Drawable)? In the Gimp, drawables are things you can draw on: layers, channels or whole images. While most functions named gimp_drawable_something operate on drawable_IDs, some functions (notably the ones operating on raw pixel data!) need a GDrawable instead. Every drawable has a corresponding GDrawable, you can get it with the gimp_drawable_get function:
gimp_drawable_something
drawable_ID
GDrawable
gimp_drawable_get
my $gdrawable = $drawable->get;
When the $gdrawable is destroyed, it is automatically flushed & detached, so you don't need to do this yourself.
Tiles are the basic building blocks of all drawables. Each drawable consists of a "grid" of tiles, each tile having the same size. The size of a tile is always the same (it's hardcoded in your Gimp program).
The gimp_tile_width and gimp_tile_height functions return the current width/height of a tile (at the moment, this is 64x64).
gimp_tile_width
gimp_tile_height
How do I get a tile? First, you have to grab a GDrawable structure. You can get one from any drawable, by calling the get function:
get
in a sense, <$gdrawable> contains all tiles. Changes you make to them might not be reflected in the image until you destroy this variable. (Thats the reason I used "my" int he above example. Once $gdrawable gets out of scope, the drawable in the gimp automatically gets updated).
To get access to a tile, you have to call get_tile or get_tile2. get_tile expects row/column numbers of the tile, while get_tile2 expects pixel coordinates and will return the tile that pixel is in:
get_tile
get_tile2
my $tile = $gdrawable->get_tile2(1,75,60);
The data method returns and sets the raw pixel data.
data
$packed_data = $tile->data; # you don't want this, use Gimp::PDL $tile->data($packed_data); # and modify the tile
PixelRgns are rectangular parts of a drawable. You can access single pixels, rows, columns and rectangles within these regions. Don't expect me to explain everything now, I don't understand the mechanism too well myself..
PixelRgn
How do I create a pixel region? First, you have to grab a GDrawable structure. You can get one from any drawable, by calling the get function:
Now you can create as many PixelRgn structures as you want from the GDrawable:
my $region = new PixelRgn($gdrawable,0,0,50,30,1,0); # with "new" my $region = $gdrawable->pixel_rgn(0,0,50,30,1,0); # or from a drawable
which method you choose is purely a question of style...
The following functions return packed pixel data (see Gimp::PDL for an easier way to manipulate on image data):
$packed_data = $region->get_pixel(45,60); # return the pixel at (45|60) $packed_data = $region->get_row(45,60,10); # return ten horizontal pixels $packed_data = $region->get_col(45,60,10); # same but vertically $packed_data = $region->get_rect(45,60,10,12); # a 10x12 rectangle
To modify pixels, the dirty bit of the region must be set (I believe, but I don't see the reason what the dirty bit in a region is for so I might be wrong), and you can write pixel data to the region with the following functions, each one corresponding to a get-function:
$region->set_pixel($packed_data,45,60); # set pixel at (45|60) $region->set_row($packed_data,45,60); # set a row $region->set_col($packed_data,45,60); # set a column $region->set_rect($packed_data,45,60,10); # a 10 pixel wide rectangle
Please note that (different to the C functions they call), the last parameter (width or height) is missing, it can be calculcated from the perl string (if you use piddles, set_rect can calculcate both dimensions from the piddle).
set_rect
Marc Lehmann <pcg@goof.com>
perl(1), Gimp(1),
To install Gimp, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Gimp
CPAN shell
perl -MCPAN -e shell install Gimp
For more information on module installation, please visit the detailed CPAN module installation guide.