GIMP Usage

Interface

• If you run the GIMP under KDE, start it in a new desktop: that's currently the only way I found to get all the GIMP windows to reappear when working with multiple applications.
• All tools have simple key shortcuts that are very useful, try to remember them.

Saving

• PNG format allows you to choose the compression level. The default maximal compression level acts strangely (artifacts on the image), so if that happens reduce the compression level to 5-6.
• Saving in XCF format (or any other format) loses all your history / undo information, so be careful.

Selection

• When making a selection, for example with the rectangle tool, you have to confirm it by clicking on it. Until this click, the selection is easily modifiable by using the sub-rectangles appearing
• A selection also usually shows the layer boundaries (which is a good thing).
• You can create a new selection based on a layer "contents" (parts that are not transparent). This is done by right-clicking on the layer and choosing "Alpha to selection".
• If you create a anti-aliased selection, this will apply to future operations. For example, a fill on an anti aliased rectangle will not fill uniformly the rectangle with the color; the edges will get a smooth transition.
• Showing grids (and activating "Snap to Grid") will greatly help with the creation of rectangles, exact circles, etc. If you want to create a shape, the best is to save a temporary selection to a path, then add or remove new selections to this path.

Gradients

• One useful gradient is the FG to Transparent one. With it you can create glossy effects easily (picking white as foreground color).

Colors

• Some color operations (like color balance) won't work on desaturated components (black or white parts of the layer).

Layers

• To copy a layer from an image to another one, you can drag and drop it from the old image to the new one. You can also do a copy and paste (but then you need to anchor the new selection that you just pasted - this will create a new layer).

• You can obtain a layer offset with the attribute myLayer.offsets (which is a Python tuple). You can move the layer by setting the offset with the set_offsets method.

Text Layers

• You can obtain the size of a text layer bounding box programmatically by calling gimp-text-get-extents-fontname. This won't actually create the layer.

Tools

• The bucket fill tool, called via the PDB interface, does not seem to work without a selection, so make a selection first. If it is a newly created layer that you want to fill entirely, it is better to use:

pdb.gimp_drawable_fill(layer, FOREGROUND_FILL)

Scripting

• Scripting the GIMP can be done easily using the Python API. You can write pure Python scripts, and you don't need to use Scheme at all.

• In order to make your Python script accessible from within the GIMP, you need to save it in ~/.gimp-2.4/plug-ins/. You need to make it executable or GIMP won't recognize it.

• In your script, you need to have the register() function and a main() function which can be empty, in addition to your actual function which executes what you want. Here are the arguments for the register function (with an example):
  • "generate_rounded_corners": Name of the plugin (how to call it programmatically with Script-Fu)
  • "This is a test Python plugin." : Textual description
  • "It creates and saves an image.": Other description (extended, not sure here)
  • "Elvanör": Author
  • "Jean-Noël Rivasseau": Copyright owner
  • "2007": Date
  • "_Rounded Corners...": Name of the plugin (in the GIMP menus)
  • "RGB*, GRAY*": Modes accepted (??)
  • []: Arguments to this plugin
  • []: Return values of this plugin, only useful in non interactive mode
  • generateRoundedCorners: Python callback function (essential!)
  • menu="<Image>/Filters/Render/Rounder Corners": Path in the menus

• In the previous list, the arguments list has the following syntax:
  • PF_STRING: type of argument
  • "targetDirectory": argument name
  • "The directory in which will be saved the images": description
  • "/srv/": Default value. This is used *only* in the interface, eg. when using the plugin non interactively you must always pass the correct number of arguments.

• The _() function that you can see used in example plug-ins is for internationalization. The "_R" in "_Rounded Corners..." is for the mnemonic, eg the key that will be associated as a shortcut in the interface.

Developing Python Scripts

• You can make your image appear on the GUI with the following command:

display = pdb.gimp_display_new(image)

• A recommended way to debug your scripts is to run each command separately in the Python console. You can also exit from a Python script by using the return() statement.

• A primitive way to get basic information displayed by your scripts is to use the gimp_message function, which will display a string on the GIMP's GUI.

Python API / Bindings

• For operations on a layer, you must add the layer to the image first. Else you will get an execution error.

• In the PDB, some functions like pdb.gimp_text_fontname allows to specify -1 as a DRAWABLE argument (to create a new layer). Using the Python API this does not work, and should be replaced with None.

• You can obtain built-in documentation about the API by using dir (gimp) in the Python Gimp shell. You should import gimpfu first.

• Another way is to use help() on a defined variable, for example a layer.

List of types in Python

• PF_INT8 = PDB_INT8
• PF_INT16 = PDB_INT16
• PF_INT32 = PDB_INT32
• PF_INT = PF_INT32
• PF_FLOAT = PDB_FLOAT
• PF_STRING = PDB_STRING
• PF_VALUE = PF_STRING
• PF_COLOR = PDB_COLOR
• PF_COLOUR = PF_COLOR
• PF_REGION = PDB_REGION
• PF_DISPLAY = PDB_DISPLAY
• PF_IMAGE = PDB_IMAGE
• PF_LAYER = PDB_LAYER
• PF_CHANNEL = PDB_CHANNEL
• PF_DRAWABLE = PDB_DRAWABLE
• PF_VECTORS = PDB_VECTORS
• PF_TOGGLE = 1000
• PF_BOOL = PF_TOGGLE
• PF_SLIDER = 1001
• PF_SPINNER = 1002
• PF_ADJUSTMENT = PF_SPINNER
• PF_FONT = 1003
• PF_FILE = 1004
• PF_BRUSH = 1005
• PF_PATTERN = 1006
• PF_GRADIENT = 1007
• PF_RADIO = 1008
• PF_TEXT = 1009
• PF_PALETTE = 1010
• PF_FILENAME = 1011
• PF_DIRNAME = 1012

Obsolete:

• #PF_INT8ARRAY = PDB_INT8ARRAY
• #PF_INT16ARRAY = PDB_INT16ARRAY
• #PF_INT32ARRAY = PDB_INT32ARRAY
• #PF_INTARRAY = PF_INT32ARRAY
• #PF_FLOATARRAY = PDB_FLOATARRAY
• #PF_STRINGARRAY = PDB_STRINGARRAY
• #PF_SELECTION = PDB_SELECTION
• #PF_BOUNDARY = PDB_BOUNDARY
• #PF_PATH = PDB_PATH
• #PF_STATUS = PDB_STATUS

• Note that you cannot currently pass an array to a Python Gimp script, since PF_STRINGARRAY has been removed (see this bug for reference). One workaround is to pass a string with special separators (like slashes), and split it into an array inside the Python code.

Launching GIMP from outside

• When loading GIMP with gimp-console for example, it will load an interpreter (the default is the Script-Fu one - but you can change that to the Python one if you want). This interpreter will then execute commands given to it (via the -b command line option for example).

• If you call Gimp from Java (via an external process), don't surround the Script-fu commands with single quotes. These are only needed if you launch Gimp from the shell, so that Gimp knows it's a string. If you use them in Java, it won't work since you will pass a string to script-fu rather than a command (Bash did not act the same way).