Gimp for the Artistically Challenged
Copyright (C) 2001, 2009 by Steve Litt, All
rights reserved. Material provided as-is, use at your own risk.
By Steve Litt
Contents on This Page
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Links on Other Pages
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I'm writing this paragraph in April 2009, when Gimp 2.4.5 is already
starting to be a little old. The rest of this web page was
written in 2001, when Gimp 1.x ruled the world. So the mouse clicks and
other procedures detailed on this web page will be a little different
than on modern Gimp versions. For instance, to get a layer list on Gimp
1.x, you rightclicked and picked Layers->Layers, channels and paths.
With Gimp 2.x you right click and choose Dialogs->Layers.
Nevertheless, this web page retains most of its usefulness, because the
underlying graphic procedures haven't changed. For instance, whether
you're using 1.6 and must rightclick->Layers->Layers, channels and
paths, or 2.x and must rightclick->Dialogs->Layers, either way,
the layer list is about the same between the versions, and you can do
the same things from the layer list. So although you can't use this web
page to blindly follow instructions, it's still very good for figuring
out how to do what you need to do.
Future additions to "Gimp for the Artistically Challenged" will be added
as separate web pages. So be assured, this information may be a little
old, but it's still very useful.
Starting and Exiting Gimp
You can start Gimp from your system menu, or with two commands, the first
of which is:
$ gimp &
The preceding command starts Gimp with no image. The ampersand on the end
runs Gimp apart from the terminal that started it. If you leave off the ampersand,
the terminal is busy as long as Gimp is running, but otherwise it's perfectly
OK. The preceding command brings up two windows that look something like this:
Note that some Gimp configurations bring up more windows. The only important
window above is the toolbox window -- the one with pens, pencils, brushes,
eyedroppers and the like. The other window is a tips window which you'll
close, although it's nice sometimes to read a few of the tips before you close
it.
Once you close it you'll see the toolbox window, which looks like this:
You can also run a command to open a file with Gimp. The following example
opens a file called wildman.jpg with Gimp:
$ gimp wildman.jpg &
That command brings up the same windows as the command without the argument,
and in addition it brings up a window with the image (in this example wildman.jpg).
The additional window looks something like this:
To exit Gimp, go to the toolbox window and choose File/Quit. This will
quit Gimp and close all open files. If any of the files is unsaved, you'll
be queried whether you really want to close unsaved files.
Loading, Saving,
Closing and Reverting Images
We already discussed how to run Gimp with an image already loaded, but to
repeat, it's:
$ gimp wildman.jpg &
The other way is to choose File/open from the menu on the toolbox window,
and navigate to the picture you want.
If you're in Gimp and want to create a new file, then from the toolbox
window's menu choose File/New, and fill out the information on the dialog
box presented to you.
To save a file in Gimp, right click anywhere in the image you're editing,
and choose File then Save or Save As. The Ctrl+S keystroke combination is
the same as File/Save.
To close a file, right click the window containing it, and choose File
then Close. If the drawing has been edited since the last save, you will
be asked whether you really want to do this.
Sometimes you make a mistake and want to revert a file to the last saved
version. Right click the drawing, then choose File and Revert. Note your
intentions are not verified, so what ever you do, never click revert by mistake.
Zooming In and Out
Pixel-exact editing requires zooming to very large magnifications. Repeatedly
pressing the equal sign key (=) repeatedly zooms in (larger magnification).
Repeatedly pressing the minus sign key (-) repeatedly zooms out (less magnification).
You can feel free to use large magnifications when drawing long lines, cropping,
selecting (marquees), because as you drag the mouse pointer, then drawing
scrolls. Practice zooming in and out until it's second nature, because when
doing pixel editing, you'll often zoom out to get the big picture, then zoom
in for accurate selections, and then out again to verify you did it correctly.
Cropping
I often like to do a rough crop, followed by a fine crop. The rough crop
can be done quickly at no magnification, and then the fine crop can be done
exactly at high magnification. That way when it comes time to do your fine
crop, you aren't distracted by junk outside the crop area.
Rough crop
At no magification (1 to 1) Move the mouse pointer to a corner significantly
outside the final fine crop area, and press shift+C. Then drag to a point
significantly outside the opposite corner of final fine crop. Then press
Enter or click the OK button on the "Crop & Resize Information" dialog
box. At this point you'll have the intended final crop area, with a small
border around it. You may wish to save your drawing (probably to another
name, if you have intentions of using the original uncropped image).
Fine Crop
This is where you crop to pixel exactitude. Start by pressing the equal sign
several times (8 is a good number) to gain magnification. Now use the scroll
bars to get to the one corner of the final crop area. Hover the mouse pointer
near the corner to be cropped, press the Ctrl+C keystroke combination, then
drag slightly to the interior of the crop area and release. You now have a
rectangular selection area with four movable corner points, as shown in the
following partial screenshot:
You'll notice that the corner you started with and its opposite corner have
no lines outside their corners, but the other two corners have lines extending
outside the corners. The points at the corners with extending lines can be
used to move the entire crop area, while the corners without extending lines
can be used to change just that corner, therefore changing the position of
just the lines coming to that corner.
Before continuing, click the "Crop & Resize Information" dialog box's
title bar and move it out of the way. You'll use it later. Now click the title
bar of the drawing, and drag the crop corner you started with to the exact
place you want that corner. Because you are at high magnification, you will
see the corner jump from pixel to pixel. In this way you can get a pixel-exact
position.
Next, drag the corner opposite the starting corner toward the opposite
corner of the final cropping area. The drawing will scroll in such a way
that you can no longer see the starting corner. Don't worry, the starting
corner will remain where you put it. When you get to the the opposite corner
of the final crop area, once again adjust the corner you're dragging in
a pixel-exact way. Once you have it pixel exact, switch focus to the "Crop
& Resize Information" dialog box, and click its Crop button. Your drawing
is now properly cropped to pixel exactness.
Cropping around two windows in a screenshot
Sometimes you need to crop two windows in a screenshot image. In such cases,
you have no landmarks for the final corner, because of the differing sizes
and positions of the two windows. In such a case, start your crop at a corner
marked by an actual window, then drag
The preceding screenshot is just such an example. I started with the lower
right corner, and need to drag to the upper left corner. But the upper left
corner is above the image of the toolbox window. So I dragged the upper left
corner to the edge of the toolbox window, and then note the little triangle
near the 0 on the horizontal ruler at the top (it would actually be at about
18 on the ruler, but the nearest numeric landmark is 0). I can now continue
to drag up, and as long as I keep the triangle in the same place, the left
side will be perfect when I finally get the top side to the proper place.
Note this works best at high magnifications, because otherwise it's hard to
know if the triangle is positioned right.
Color Reduction
There's exactly one reason for color reduction -- reducing bandwidth. Because
of the compressive nature of .jpg files, color reduction does little to reduce
the size of .jpg files. Color reduction is most effective reducing the size
of .png and .gif files. Note that because .gif files are covered by a patent,
you should not create new .gif files, and should take steps to convert your
old .gif to .png.
But anyway, here's a script, called 256, which reduces the depth of a .png
to 256 colors.
#!/bin/sh convert -depth 24 $1 $1 convert -depth 16 $1 $1 convert -depth 8 $1 $1
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and here's another script, called 16, which reduces the depth of a .png
to 16 colors:
#!/bin/sh convert -depth 24 $1 $1 convert -depth 16 $1 $1 convert -depth 8 $1 $1 convert -colors 16 $1 $1
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The reason we convert down gradually is to get the best color simulation.
Also, always crop before you color reduce, so that extraneous colors
that got cropped away don't influence the color approximations.
Making Pixel
at a Time Changes With a One Pixel Brush
Note: If you're having trouble creating exactly sized selections required
to create these shapes, take heart. The next
article explains how to resize selections. But let's do the simple stuff
first...
If you're anything like me, you need a pixel editor to edit a pixel at
a time. Gimp's defaults involve pencils and brushes that draw broad strokes.
To do pixel by pixel editing, you need to choose a single pixel brush. Start
with a drawing you have open, and then:
- On the toolbox window, click the pencil ().
- Right click the drawing, choose Dialogs and then Brushes, and you'll
be brought to the following brush choice dialog:
- Click the
single point brush, as shown above, and you'll see the display change to "Circle
(01) (1 x 1) as shown following:
- Now anything
you draw with the pencil will be one pixel wide.
Drawing Straight Lines
Straight lines are drawn with the pencil. You should start by picking the
proper brush, as described in the preceding section.
- Select the pencil tool ().
- Select the proper brush as described in Making Pixel at a Time
Changes With a One Pixel Brush.
- Click and release EXACTLY where you want your line's starting point.
A single point will be drawn. You must be exact, because you will have no
opportunity to move or change that point. You might want to make that point
at a high magnification.
- Move the mouse, and then depress the shift key. You'll see a construction
line appear between the starting point and the mouse pointer. That line will
move as you move the mouse. When you have the mouse pointer exactly where
you want the end of the line to be, click once more. The line will be created.
Note that if you continue to depress the shift key, and continue to move
the mouse, a new construction line will extend from the end of the previous
line to the mouse pointer. In this way you can easily draw complex multiline
shapes. You can fill those shapes with the bucket tool ().
Drawing Rectangles and Ellipses
To draw a hollow rectangle:
- Create a rectangular selection, whose dimensions are what you want the
final rectangle to be, with the "Select rectangular regions" tool ().
- Choose the proper brush width, as explained in "Making Pixel at a Time
Changes With a One Pixel Brush".
- Right click anywhere on the drawing, choose Edit, and then choose Stroke.
Notice that a hollow rectangle has been formed, with its lines half inside
and half outside the original selection.
To draw a hollow ellipse, follow the instructions for the hollow rectangle,
except use the "Select eliptical regions" tool ().
To draw a filled rectangle or ellipse, create the rectangular or elliptical
selection, and then use the bucket tool () inside of it.
To create a filled rectangle or ellipse with a border, draw a hollow rectangle
or ellipse with the border color, click "Select rectangular regions" tool
(), click outside the
current selection to "turn off" the current selection, choose the fill color
with the color picker and foreground/background color tool (, ), and then use the bucket tool
() to "pour" that color
inside the already created hollow rectangle or ellipse.
NOTE
To save time filling selections, instead of switching to the bucket
tool, you can simply right click inside the selection, and choose Edit->Fill
with FG color. There's an Edit->Fill with BG color to save
you even more time.
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Resizing and Moving Selections
Resizing selections is one of Gimp's few weak points. In many draw and paint
programs you simply drag the selection. It's not as simple in Gimp. In fact,
it's tough enough that you might want to try extra hard to get the selection
exactly right the first time.
Moving a selection
To move a selection, without moving the content it encloses, press the Alt
key and drag the selection.
Be aware that dragging a selection moves the actual content contained
by the selection. That's probably not what you want.
Because moving a selection is much easier than resizing one, and because
resizing can be done only one side at a time, it's best to move the selection
so one of its corners is in the exact correct place. Then you'll need to
resize at the most 2 sides. If you didn't move first, you might need to resize
3 or 4 sides. So always move the selection until one of its corners is in
the right place. The easiest way to exactly position a corner is to move
it close to the correct location at no magnification, then press the equal
sign several times so each pixel of movement is obvious, and position it
exactly.
To enlarge a selection
The only way to enlarge a selection is to move one side at a time. The side
isn't really moved. Instead, an additional selection is drawn such that the
additional selection will be "added" to the edge of the first one. That implys
that the second selection must be exactly the same width as the first, and
it must be exactly aligned. Exactness implies great (like 8x) magnification.
Because Gimp scrolls the screen to accommodate dragging, the magnification
is practical.
So here's the procedure for extending a rectangular selection farther
down from the bottom:
- Magnify the screen 6-8 times with the = key.
- On the toolbox, click the rectangular selection tool ().
- Locate the lower left corner of the existing selection.
- Place the mouse pointer a few pixels straight up from the bottom left
corner, meaning the pointer is on the line defining the left side of the existing
selection.
- Depress the shift key, and note that the mouse pointer now has a plus
sign (+).
- Drag several pixels down and to the right. Note that the new selection
grows as a square, not as a rectangle.
- While still holding the mouse button, release the shift key, and note
that you can now drag down or right as you please.
- Drag down to the the desired bottom of the grown selection.
- Note the exact number that the left hand triangular ruler mark rests
on. This is how you will make sure that when you drag right you don't drag
up or down.
- Drag right until the right side of the new selection overlays the right
side of the original selection.
- Drag up or down until the left hand triangular ruler mark rests on the
same number as it did when you dragged down the desired distance.
- Release the mouse button, and note that you've grown the rectangle perfectly.
- Reduce the magnification with the minus key (-)
A few comments on the preceding procedure. First, you could have used similar
procedures to grow it right, left, or up. Second, in any type of dragging,
the rulers on the top and left are your friend. The higher the magnification,
the more likely those marks will be exact to the pixel.
To shrink a selection
The procedure to shrink is basically the same, except you use the Ctrl key,
which gives the mouse pointer a minus sign, and also you start from the point
you want to be the bottom:
- Magnify the screen 6-8 times with the = key.
- On the toolbox, click the rectangular selection tool ().
- Locate the lower left corner of the existing selection.
- Move up the left edge of the original selection to the point that should
be the new bottom, and place the mouse pointer at that point on the left
side of the original rectangle.
- Depress the Ctrl key, and note that the mouse pointer now has a minus
sign (-).
- Drag several pixels down and to the right. Note that the new selection
grows as a square, not as a rectangle.
- While still holding the mouse button, release the shift key, and note
that you can now drag down or right as you please.
- Drag down to the the desired bottom of the grown selection.
- Drag down until the bottom of the new selection overlays the bottom
of the old selection.
- Drag right until the right side of the new selection overlays the right
side of the original selection.
- Release the mouse button, and note that you've shrunk the rectangle
perfectly.
- Reduce the magnification with the minus key (-).
Irregular grows and shrinks
One cool thing about this is you can grow and shrink in irregular patterns,
and even on elliptical curves. To explore this, try growing and shrinking
but not matching the sides, and notice that you can make "dimples". And if
you use the eliptical selection tool (), those dimples can be curved. Experiment.
Using Layers
Gimp is pixel based -- not vector based. Vector based graphics have the advantage
of being able to move image parts as objects rather than groups of pixels.
That means you can pile objects on top of each other and later separate them
again, without damaging the image parts below the object. Just try that in
most pixel based graphic programs.
But Gimp has layers, and used right, you can gain that same advantage.
For instance, take the cover of my new (as of December 2001) book, "Troubleshooting
Techniques of the Successful Technologist". It was designed in Gimp. Here's
a smaller version of the book's cover design:
Here's what my layers look like:
Layer |
Contains and portrays |
Background |
Contains the rectangular box whose left side is thicker than the
others. Note that this box DOES NOT feature rounded corners |
corners |
Contains shapes which, when properly placed over the box's corners,
give the box rounded corners |
const lines |
A layer for drawn construction lines. Note that the eyeball is missing
from this layer, as the final product should not show the drawn construction
lines. Note also that in most cases construction lines should be dragged
from the rulers, not drawn |
title |
Contains the 2 line title plus the author's byline. |
utp_ad |
Contains "Includes full Universal Troubleshooting Process documentation",
and the 10 steps of the Universal Troubleshooting Process |
divcon |
Contains the divide and conquer symbol (square iteratively cut further
in half, and the legend "A Troubleshooters.Com Publication" |
In this way I can move the various elements around without jeopardizing
other elements. For instance, I can select the divide and conquer symbol
and place it on top of (or beneath if I rearange the order of the layers)
the 10 steps. And then later I could move it elsewhere without disturbing
the 10 steps.
Using layers, you can simulate the "objects" of vector drawings in all
manner except shrinking and growing.
Retroactively
Making a Layer Transparent
All you want to do is scan a signature written in black pen, then put a light
blue line under the signature. Sounds trivial, but it's not obvious.
What won't work is simply drawing a line -- the line will overwrite
the signature instead of underwriting it.
Gimp Guru Andrew Wyatt contributed this excellent solution. Do the following:
- From Gimp, File->Acquire->Sane to create an image of the signature.
- Rightclick, Image->Alpha->Add alpha channel, in order to make
this layer transparent.
- Rightclick, Select->By color.
- In the image, click in the white portion, in order to select everything
white.
- Rightclick, Edit->Clear, in order to clear selected material to transparent.
- Rightclick, Select->None, in order to clear all selections. You now have the signature on a transparent background, and
are ready to save.
- Rightclick, Layers->Layers, channels and paths.
- Create a new transparent layer called "line" and move it to the bottom.
- Draw your blue line on that layer.
- Rightclick, Layers->Layers, channels and paths.
- Create a new, white layer called "white" and move it to the bottom.
If you don't like the light gray outlines between the black letters and the
blue lines, manually set the offending pixels to transparent, or else to a
darker blue. If doing it manually doesn't float your boat, you can do it automatically,
although it will require some trial and error. Here's how:
- On the signature layer, select the area above the blue line.
- Magnify greatly, and find the lightest pixel sitting atop the blue line.
This will be your color to select by.
- Right click, Select->By color
- On the By Color Selection screen, click the Intersect
radio button, and set Fuzziness Threshold to a moderate value -- something
like 36.0. The higher you set this figure, the more pixels will be cleared.
- Click the Close button on the By Color Selection screen.
- Right click, Select->By color
- Click the lightest pixel sitting atop the blue line. This will highlight
the lightest several pixels sitting atop the blue line, while leaving darker
pixels, and all pixels not sitting atop the blue line, alone.
- Right click, Edit->Clear, in order to clear these light pixels and
let the blue line show through. The result is a more realistic looking signature
over line, without the telltale light gray outlines.
- If any annoying light gray outlines remain, repeat this procedure on
top of all or part of the blue line. So in the screenshot immediately above,
I might want to get rid of the gray above the bottom of the S, and below the
bottom of the L.
Using Gimp to Fill In .pdf Forms
Some .pdf forms allow you to fill them in, but most don't. In the old days
your choices were a pen or a typewriter -- neither particularly appetizing.
Now you can use Gimp to fill in the forms.
What you're going to do is open the .pdf in Gimp, place a transparent
layer on top of the form, type the information on that transparent layer
in the blanks provided, and save as a native Gimp document (.xcf).
Short Instructions
For those of you who regularly use Gimp and just need a quick reminder of
how to do this process, here are a short set of instructions:
- Open the .pdf in Gimp
- Choose 150dpi, heavy text antialiasing, light graphic antialiasing
- Each page becomes a separate drawing
- Save each page as a .xcf (Gimp native)
- Create a new layer called "typewriter", transparent, on top, and save
again
- Choose the "typewriter" layer.
- Use the text tool to fill in the blanks (on the "typewriter" layer)
- Edit as necessary, save frequently
- Print
- Save as xcf, and for posterity save in a ubiquitous format like .jpg.
Complete Instructions
Here are the complete step by step instructions:
- Open the .pdf in Gimp
- Choose 150dpi, heavy text antialiasing, light graphic antialiasing as
follows:
- Click OK, and notice that each page becomes
a separate drawing
- Save each page as a .xcf (Gimp native)
- For each page, do the rest of the steps...
- Right click drawing and choose File/Layers/Layers, Channels & Paths...,
and note that the "Layers, Channels & Paths" dialog appears, as shown
following:
- Click the "New Layer" button () to bring up the New Layer Options dialog,
as shown following:
- Name the new layer "Typewriter" and make sure the Layer Fill Type is
"Transparent". The width and height should default to the right quantity.
- Click the OK button to return to the "Layers, Channels & Paths"
dialog, and note that the Typewriter layer appears above the Background layer
(if it doesn't, use the up and down buttons to fix that):
- Click the Typewriter layer line to choose it. This means
that editing will be done on this layer until you use the "Layers, Channels
& Paths" dialog to choose a different layer.
- Right click, then File/Save as, and choose a name with the extension
.xcf, which is the extension for native Gimp files. Make sure the "Determine
File Type:" choicefield reads "By Extension", and then click OK to
save the file.
At this point you have the equivalent of a layer of clear plastic wrap on
top of your form. You can write to your hearts content on the wrap, and erase
it without erasing the form. This means you can move text around at will without
changing the form itself.
To fill in the form, simply use the text tool, on the Typewriter layer,
to fill in the blanks. Edit as necessary, save frequently. When finished,
you can print your .xcf file and you get an almost perfect reproduction (it
will be a little smaller than the original, and I haven't figured out a way
to get around that yet).
As already stated, you save it as an .xcf file so you can work on
it some more, or use it as a template for something else later on. However,
you might also want to save it as a .jpg, because the .xcf format is very
unusual, and its possible in 10 or 20 years Gimp won't exist, but you know
there will be tools to retrieve .jpg files.
Construction Lines in Gimp
Gimp's rulers and high magnification potential make it perfect for exacting
work. Sometimes you need construction lines in order to complete that work.
There are two ways of making construction lines in Gimp:
- Real Gimp construction lines
- Drawn lines on a different layer
By far the easier of the two is to use the construction lines provided by
Gimp itself. To make a horizontal construction line all the way across the
drawing, click the top ruler and drag the horizontal construction line where
you want it. The construction line will not show in printouts. You can move
the construction line any time you want by clicking the "Move layers &
selections" button (), and then dragging the construction line.
Be careful though, because if you miss the construction line, you'll drag
the entire selection or frame, which is the last thing you want to do. If
that happens, Ctrl+Z undoes the last action (and there's an undo stack, so
you can undo several actions). But the good news is that when the little pointing
finger is on the construction line, the construction line changes colors.
Construction lines can be moved in any layer, even if it's a different layer
than the one in which they were created. This is a time saver.
To make a vertical construction line, click and drag the left ruler, and
manipulate it the same way you would a horizontal construction line.
Construction lines survive sessions. To get rid of construction lines,
just drag them back to the rulers.
Occasionally you might want your construction lines to be drawn lines.
Perhaps you don't want them going all the way across the screen, or perhaps
you want them to print on your printer in certain situations. In that case
you can draw them as actual lines on their own layer (I call the layer const_lines).
You can show and hide the lines simply by clicking the eyeball (or the place
where the eyeball would be) on the layer dialog box. NEVER make drawn construction
lines on a layer containing graphics, as it would be impossible to separate
them from the graphic.