Gimp::Pixel - how to operate on raw pixels.
***WARNING*** this manpage is no longer up-to-date. See examples/map_to_gradient for a simple raw-pixel-manipulating plug-in. If you bug me enough I'll rewrite this document.
use PDL; # to make sensible things with the pixels
# Gimp::GimpDrawable - The GimpDrawable 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::GimpDrawable, Gimp::Tile, Gimp::PixelRgn) are available with and without the Gimp:: prefix.
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 GimpDrawable instead. Every drawable has a corresponding GimpDrawable, you can get it with the gimp_drawable_get function:
my $gdrawable = $drawable->get;
When the $gdrawable is destroyed, it is automatically flushed & detached, so you don't need to do this yourself.
Tiles are the basic building blocks of all drawables. Each drawable consists of a "grid" of tiles, each tile having the same size. The size of a tile is always the same (it's hardcoded in your Gimp program).
The gimp_tile_width and gimp_tile_height functions return the current width/height of a tile (at the moment, this is 64x64).
How do I get a tile? First, you have to grab a GimpDrawable structure. You can get one from any drawable, by calling the get function:
in a sense, <$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:
my $tile = $gdrawable->get_tile2(1,75,60);
The data method returns and sets the raw pixel data.
$piddle = $tile->data; # get the tile data as a piddle
$piddle *= 0.5; # do sth. with the pixels
$tile->data($piddle); # 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..
How do I create a pixel region? First, you have to grab a GimpDrawable 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 GimpDrawable:
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):
$piddle = $region->get_pixel(45,60); # return the pixel at (45|60)
$piddle = $region->get_row(45,60,10); # return ten horizontal pixels
$piddle = $region->get_col(45,60,10); # same but vertically
$piddle = $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:
$region->set_pixel($piddle,45,60); # set pixel at (45|60)
$region->set_row($piddle,45,60); # set a row
$region->set_col($piddle,45,60); # set a column
$region->set_rect($piddle,45,60); # set a whole rectangle
Please note that (unlike the C functions they call), the size arguments (width and/or height) are missing, they can be calculated from the piddle.
Marc Lehmann <email@example.com>
To install Gimp, copy and paste the appropriate command in to your terminal.
perl -MCPAN -e shell
For more information on module installation, please visit the detailed CPAN module installation guide.