donhatchnotes/gimp at master · donhatch/donhatchnotes · GitHub

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Doc:
    http://www.gimp.org/docs/
Tutorials:
    http://www.gimp.org/tutorials/


LAYERS
    Layers are like stacked transparencies
    Layers Dialog: Dialogs->Layers, or ctrl-L
    Select a layer in this dialog to make it be the one affected by operations.
    Turn on&off the eye of a layer to make it visible/invisible in the image window.
    (shift-click a layer's eye to make it the only one visible)
    The chain-link icon of a layer (between the eye and the picture of the layer)
    is used to group the layer with other layers, for operations on multiple
    layers (for example with the Move tool or a transform tool).

    The active layer is shown as an outline in black&yellow
    (whereas the current selection is black&white)

    Re-stack layers by using up and down arrow buttons in Layers dialog.
    "Merge down" by selecting Merge Down in layer's right-mouse menu

    When you paste something, it becomes a "Floating Selection (Pasted Layer)";
    to make it permanently part of the image, hit the Anchor in the Layers dialog
    (or ctrl-H, or click outside the selection).

    Introduction to layers in manual is in section 8.1: Intro to Layers
        http://docs.gimp.org/2.6/en/gimp-image-combining.html#gimp-concepts-layers
CHANNELS
    Dialogs->Channels
    controls which channels are affected by operations, and which are visible
    in the image window.
    by default all channels (r,g,b,a) are affected and visible.
    Can turn off&on channels being affected by clicking on the right,
    or turn off&on their visibility in the image window by clicking their eye.

COMPOSITING
    This tutorial is excellent ("Simple Floating Logo" tutorial from tutorials page):
        http://www.gimp.org/tutorials/The_Basics/
    although you have to google to find what menus some of the effects
    live in.


UNANSWERED QUESTIONS:

Q: when I read in a multi-page pdf file, each page
   becomes its own layer. how do I save all these back out
   into a pdf file?
PA: some references say print-to-file, but that produced
   a pdf that acroread couldn't read back in :-(

Q: what's the difference between the crop and resize buttons, in
   the crop info window after I've dragged out a crop region?

Q: the background layer doesn't have an alpha channel,
   added layers do.
   I can add an alpha channel via right-click-on-layer -> Add Alpha Channel
   But how to remove one?
   Wtf?  The docs say there's supposed to be a menu item for "Remove Alpha Channel"
   but there isn't one???

ANSWERED QUESTIONS:

Q: sometimes when I paste, creating a Floating Selection,
   it lets me drag the position around, and move it with arrow keys,
   but sometimes not... ??? (when in Rectangle Select Tool)
A: not sure, but switching to "Mode Tool" seemed  to fix it

Q: how to tell the dimensions of an image or layer?
A: <Image> View -> Info Window

Q: how to crop an exact rectangle out of an image?
A: crop tool (the little knife in the toolbox)
   drag out an approximate rectangle
   adjust its size by dragging upper-left or lower-right handle,
   or its position using upper-right or lower-left
   zoom up so can see the pixels
   hit the crop button

Q: I seem to have got it in a mode where,
   when I try to drag out a rectangular selection,
   it just moves the previous one.  How to get out of that mode?
A: hmm, probably the whole image is selected then.
   start the drag *outside* the selection region (or just click there).
   (or Select->None).
   once the selection is made smaller or nonexistent,
   it will become manageable again.

Q: how do I make "=" zoom in??? it used to, wtf :-(
A: the help for + (view->zoom release mouse, hover over '+', F1)
   acknowledges this is controversial, and to make a dynamic shortcut.
   Edit -> Keyboard shortcuts -> View -> Zoom in
       Q: there are two of them?  view-zoom-in and view-zoom-in-accel
       A: oh fooey, they aren't really both +; one is + and the other is
          numeric-keyboard-+.
          Okay so I'll reassign the first one to be = instead.
   Note: I also unchecked "save shortcuts on exit".  I like explicit.

Q: how to see what rgb color is under the cursor?
A: Pointer dialog