[Courses][gimp] Lesson4: Basic selection tools, and copy/paste

[Julie Sloan]

For my homework I used a picture I took last summer of my tabby-point 
siamese (is there such a thing?) Shorty:

http://www.bobsloansampler.com/gimp/shorty1.jpg I used the elliptical 
selection tool and added a drop shadow

http://www.bobsloansampler.com/gimp/shorty2.jpg I tried getting rid of the 
background using a combination of the color selection and contiguous region 
selection tools, then I discovered by accident that the erasor tool will 
work inside a selection and leave the outside stuff alone.  

I ended up with a white circle with a cat innit  :) which is 
http://www.bobsloansampler.com/gimp/shorty3.jpg and

in http://www.bobsloansampler.com/gimp/shorty4.jpg I discovered the opacity 
slider bar in the Layers, Channels and Paths dialogue and put lots of 
little ghost cats all around.

My original is http://www.bobsloansampler.com/shorty.jpg

This is fun; sorry if I'm being a bit silly with it.

Julie



On Friday 18 February 2005 04:56 pm, Akkana Peck wrote:
> In this lesson we'll explore some of GIMP's basic selection tools,
> and some tricks for combining several images.  I'll conclude by
> showing how to paste Tux, the Linux penguin, into photos.
>
> I'll start with a photo of the Mitten Fault on the Green River
> in Utah's Dinosaur National Monument:
> http://shallowsky.com/images/gimpcourse/lesson4/mittenfault.jpg
> (that's a scaled-down version for the web.)
>
> It's a cool place.  But one thing you can't easily see in the
> scaled-down version: down by the sandbar in the lower right quarter
> of the picture are two kayakers coming down the river.  I'd like
> to show a magnified version of those kayakers on the same image
> that shows the whole scene.
>
> I start by loading the full-sized image into gimp.  But I'll need
> to work with both the full sized version and a scaled-down copy,
> so the first step is Image->Duplicate to make a second copy.
> (Of course, I could also use cp in the shell, then open that
> file in gimp.)  Then I scale the copy much smaller, 550 pixels wide.
>
> The next step is to go back to the original image and select the
> kayakers.  I'll use the simplest selection tool for this: the
> rectangular selection tool, the very first tool in the gimp toolbox.
> (It's probably already selected by default when you start gimp.)
>
> Go to the large image, and select as though you were using the
> Crop tool: start at the upper left of the area you want, mouse down,
> and drag down to the lower right.  Gimp will draw lines to show you
> the box while you're dragging out the selection, and when you release
> the mouse button, the selection is shown by a black-and-white dashed
> line where the blacks and whites continuously change.  In gimp
> parlance, this line is called the "marching ants".
>
> Gimp's selection tools aren't as smart as crop, so you can't change
> a selection's size easily once you've made it.  (You can move it;
> I'll talk about that later.)  So if the selection you made isn't quite
> right, click somewhere outside the marching-ants box (this will cancel
> the selection) then try again, until you get the selection where you
> want it.  (Be careful about clicking inside the selection: if you
> click inside a selection then drag, gimp moves the contents of the
> selection and leaves a white rectangle behind, which is almost never
> what you want.  If this happens accidentally, Undo will fix it.)
>
> When you have a selection, lots of things act a little differently in
> gimp.  Most filters (for instance, the brightness tools discussed in
> lesson 2) will only act on the selection, not the rest of the image;
> and most drawing tools won't draw outside the selection.  We'll use
> that for some useful effects later.
>
> For now, though, what I want to do is copy the selection from the
> big image, then paste it into the small image.  So I copy it:
> Edit->Copy, or just ctrl-C.
>
> Now I can go to the small image, and paste it: Edit->Paste, or ctrl-V.
>
> What happened?  It pasted the selection as a new layer in the smaller
> image, which you can see in the Layers dialog: it probably says New
> Image, or Pasted Image.  But it's a Floating layer, which may not be
> obvious from the name.  Gimp 1.2 will call it a Floating layer, but
> gimp 2 just shows marching ants to show that it's different from a
> normal layer (so it looks just like a selection).  Click the New Layer
> button in the Layers dialog now to make it a normal layer.
>
> The rectangle didn't paste at the place where I wanted it.
> So the next step is to move it.  I can do that by selecting the move
> tool: the same crossed arrow icon in the toolbox that we used to move
> the text layer around in lesson 3.  Using the move tool, I'll drag my
> box down to the green area in the lower right of the image.
>
> What if I want to see what the image looks like without that
> dotted-line layer boundary?  Selecting the other layer (probably
> called "Background") in the layers dialog will draw the outline
> around that layer (the whole image) instead of the smaller layer.
>
> Now I have my little box showing kayakers pasted on top of my
> scaled-down image.  But it looks weird -- it's hard to tell that
> that rectangle is something I put there intentionally.  So how
> can I fix that?  Easy: add a drop shadow!
> (Script-fu->Shadow->Drop-Shadow... just like in lesson 3.)
> I could even use a different color for my drop shadow to make it stand
> out more, though in this case I couldn't find one that didn't look
> garish.  If I save the image now as jpg (of course I have to let gimp
> export it since I now have multiple layers), it looks like this:
> http://shallowsky.com/images/gimpcourse/lesson4/mittenfault-insert.jpg
>
> But rectangular isn't the only type of selection gimp has.  Right next
> to the rectangular selection tool is ellipse select.  It works the
> same way as rectangular select, only it lets you make ovals and
> circles instead of rectangles and squares.
>
> If I follow exactly the same procedure as before, but I use ellipse
> select instead of rectangular, and play with the drop shadow color,
> I get the rather strange looking:
> http://shallowsky.com/images/gimpcourse/lesson4/mittenfault-ellipse.jpg
>
> To close the lesson, I'll talk about one more selection tool:
> well, actually two closely related ones, Select Contiguous Regions
> and Select By Color.  And who better to introduce these useful tools
> than everybody's favorite penguin?
> http://shallowsky.com/images/gimpcourse/lesson4/tux-large.gif
>
> (Incidentally, Tux was created by Larry Ewing, drawn freehand in
> gimp version 0.54.  It's legal to use him or make changes as
> long as you credit Larry Ewing and the GIMP if anyone asks.
> The artist has a page describing how he was drawn:
> http://www.isc.tamu.edu/~lewing/linux/notes.html )
>
> Now, Tux is cute all by himself, but what if I want to take him
> along on my trip to see the Mitten fault?
>
> First I decide how big he'll need to be.  100 pixels high looks about
> right; so I scale Tux to that size.
>
> Next, I need to select Tux (but not the background around him),
> so I can paste him into the photo.
>
> To do that, I need to select Tux himself, and not that white
> background behind him.  (Or I could go download a tux image that
> already has a transparent background from Larry Ewing's page --
> but then we wouldn't have this part of the lesson! :-)
>
> To do this, I choose the toolbox icon that looks like a magic wand
> with a light on the end, with the tooltip "Select Contiguous Regions".
>
> This tool will select everything that's of similar color to the place
> where I click.  How close it needs to be is defined by the Threshold
> in the tool options: if you set Threshold to 0, then only identical
> colors will be selected.  For this particular example, make sure
> Feather Edges is turned off.  What I'll do is select the background,
> because it's all one color, whereas Tux isn't.
>
> A very similar tool is Select by Color.  In gimp 2 it's in the
> toolbox right next to Contiguous Regions; in 1.2 it's in the menus,
> Select->By Color.  If you click on a white pixel, then EVERY white
> pixel in the image becomes selected.  Try it on Tux!  You won't want
> it for this exercise, but it's a very useful tool for some images.
>
> With the Contiguous Regions tool chosen, I click anywhere in the white
> background.  Voila!  I see marching ants around the edge of Tux, and
> also around the outside edge of the image.  The background is now
> selected.
>
> But I don't actually want the background, I want Tux himself.  I want
> the selection to be the exact opposite of what it is.  That's easy to
> fix: Select->Invert.  Now Tux is selected: I still see the marching
> ants around him, but no longer see them around the edge of the image.
>
> Now I'm ready to Copy, then Paste into the photo.  Click on New Layer,
> select the move tool, drag the Tux layer to where I want him ...
> and voila, Tux Visits the Mitten Fault!
> http://shallowsky.com/images/gimpcourse/lesson4/mittenfault-tux.jpg
>
> Homework:
> Select something from one image (using any selection tool) and paste
> it into another image.
>
> Next lesson: basic drawing tools.
>
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