Gimp Image Editor

[last updated: 2024-04-07]
Gimp: Installation & Basic Operation
Gimp: Draw Elements
Gimp: Text
Gimp: Advanced Operations
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On This Page:

crop an image
resize an image
add whitespace around an image
delete or move or rotate a selection
scale a selection
skew perspective
paint over something to match the background
change colors
measure angles
insert an object into another drawing

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Crop an image:
- File > open, navigate to desired file,
  click to select it then <Open>, or just double-click
  Windows tab (top menu bar) > new toolbox
  rectangle select tool (top left icon in toolbox)
  click and drag around selection desired
- Image tab (top menu bar) > Crop to Selection
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Resize an image:
Image -> Scale Image
"lock" icon to preserve WxH proportions
scroll up or down to desired pixel size
click "Scale"
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Add whitespace around an image:
- Image > Canvas Size
  "lock" icon is active to preserve WxH proportions
  use up arrow to increase pixel size
- In Canvas Size dialogue, under 'Layers',
  select 'All Layers' and 'Fill with Background Color'
  Click ReSize
- Re-center image:
  Tools > Selection tools > Rectangle Select
  Drag around image
  Edit > Cut
  Edit > Paste
  drag selection to desired location
  Layers -> Anchor Layer
  re-crop if desired
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Delete or Move or Rotate a section of a drawing:
Tools - Selection Tools - Rectangle select
Click-and-hold, drag, and release to define the rectangle around the section you want to operate on
- to delete: Edit - Cut
  left-click somewhere in the drawing
  then Select -> none to clear the floating selection
  Note this leaves a "hole" with no background
- to move: Edit -> cut, then Edit -> paste
  click & hold in the selection,
  drag to new location, and release click to drop
  Layer -> Anchor layer
- to rotate:
  Tools - Transform Tools - Rotate
  enter angle desired, click Rotate
  Layer -> Anchor Layer
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Scale a selection:
- Select area to scale:
  Tools -> Selection Tools -> Rectangle Select
  Drag window around desired selection
  - The following instruction came from the web somewhere, however it does not seem to be necessary with the Gimp version I have, since scaling directly without creating a floating selection worked just fine.
    - Create a "floating selection":
      Select -> Float
      (or Shift + Ctrl + L)
- Scale your selection:
  Tools -> Transform Tools -> Scale
  Drag a corner or side box, or enter numerical
  Click Scale
- Layer -> Anchor Layer
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Skew perspective:
- Open drawing
- Create Guidelines
  (These are not strictly necessary, but if you want your skewed perspective to end up being perfectly vertical or horizontal, they help.)
  - position cursor over ruler at either top or side of workspace,
  - click/hold left button and drag guidelines to desired location in your image,
  - assuming you have a skewed image that you're trying to "straighten",
    position the guidelines where the new, straightened sides of your image will be after being adjusted.
    Remove them with: Edit --> "Undo Add Vertical Guide"
    or - Image --> Guides --> "Remove All Guides"
- Click Perspectve icon (3d wire-frame cube), then click in image, or
  Tools → Transform → Perspective
- Note perspective dialog box opens
  Note perspective diamonds appear in corners of your image
- Note Perspective parameters are shown in left side-bar menu.
  Defaults will likely be acceptable:
- Drag corner diamonds to adjust perspective as desired.
  Hold shift key so that drag direction is perfectly horizontal, vertical, or 15deg increments
- Click Transform in Perspective dialog box to execute
- You will need to crop out any unwanted white space that is created
- Remove guides and export
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Paint over something to match the background:
Edit - Preferences - Toolbox - Clone - OK
position clone source select circle over an area of the background you want to capture
hold Ctrl and click to select
move clone paste circle over area you want to replace, click
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Change Colors:
- ... of next entities to be drawn:
  - At the top or bottom of the toolbox there is a pair of colored squares.
    The one in top left, that overlaps the one in the bottom right, is the foreground color.
    The one in bottom right is the background color.
  - To change them, click on the square you want to change (foreground or background).
    A color pallete opens.
    Either drag the RGB sliders to find what you want,
    or drag the C & H sliders.
    Notice the cross-hairs in the left block,
    and the color shown in "Current" block at the bottom
    track changes you make to the sliders.
    You can also click directly in the left block,
    or click in the vertical color bar at the right of the left block.
  - When the "Current" block at the bottom shows the color you want, click OK
  - To save your current color as a preset, click and hold on the current color block
    and drag and release at one of the 12 preset blocks to the right. Click OK.
- ... of previously drawn entities or background ...:
  - ... bucket fill
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Measure Angles:
- Note: You cannot just select objects in your drawing and measure their angles.
  You must first draw a "measure line" coincident with or parallel to your line of interest,
  then measure the angle of your "measure line."
- click Tools -> Measure, or shift-M
  the compass icon will appear.
- Position cursor over desired start of first measure line,
  press and hold shift,
  click and drag cursor to endpoint of measure line,
  release click and shift.
  Move cursor slightly away from endpoint.
  and Notice the angle from vertical
  will be displayed in bottom status bar.
- Notice that angle numbers are always positive,
  regardless of whether CW or CCW from vertical.
  ---------------
- Measure angle between two arbitrary lines:
  - As above, position cursor, press and hold shift, click and drag to define first measure line, then release click and shift.
  - Position cursor over measure-line endpoint that you desire,
    press & hold shift
    click and drag to create second measure line,
    release click and shift, and move cursor slightly away.
  - Notice angle between the lines is displayed in bottom status bar.
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Insert/Overlay an object into another drawing:
- Open a drawing
- Open the drawing or image that you want to insert into the first drawing.
- Windows -> select first drawing,
  Layer -> New
  enter desired name
  default Opacity will be 50%. Change to 100% if desired
  click OK
- Windows -> select drawing/image to insert
  Select -> All
  Edit -> Copy
- Windows -> select first drawing
  click on new layer in right-hand sidebar layer block
  Edit -> Paste

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