Hello again and welcome back to our course on PSE 15.
In this section we’re going to continue looking at Selection Tools and this time we’re
going to look at Drawing Selection Tools.
The Drawing Selection Tools are collectively known as the Lassos.
They’re the third group of tools in the Selection section in the toolbox.
We have the Lasso, the Magnetic Lasso and the Polygonal Lasso.
These tools work on the basis of drawing around the item, object or whatever that needs to
be selected.
And in fact looking at this picture of the sheep in the field, if I wanted to select
the sheep the drawing selection tools are probably not the tools that I would use.
So why wouldn’t I use them for this sheep?
Well the sheep has a couple of distinct advantages when it comes to selection.
First of all it has a pretty distinct edge and secondly there are significant color differences
between the sheep and the surrounding field, the grass, etcetera.
So there are other much more suitable tools for selecting this sheep.
You tend to use the drawing selection tools when you don’t have distinct edges or when
the edges even if in some places they’re quite distinct in others they aren’t.
And also where you don’t have the same kind of distinct color differences.
There’s much more of an element of you needing to draw around the selection in order to define
what the selection is.
So I’m going to use the drawing selection tools on a different image altogether.
So let me take as an example this picture of the horses in the field and let’s suppose
that I wanted to just select the horses more or less in the middle of the picture.
First of all when it comes to selection it’s a good idea to zoom in as far as you can because
it will generally make it much easier to apply the relevant tool and certainly the tools
that involve you in doing some drawing.
So let me just zoom in.
Now one of the things that would make this particular horse quite difficult to select
is that it has a rug on and differentiating between the edge of the rug, the horse next
to it, the horses legs, the mud, most of the more are automated selection tools would really
find that pretty difficult.
So what I’m going to do is to use the lasso tool and I’m going to draw around the area
that I want to select.
Now before I start one or two very important points.
One of them is with a fairly complicated subject like this how good the selection is pretty
much totally depends on how good you are at keeping a steady hand but also on you taking
a little bit of time to do the job.
As you’ll see later on there are ways of refining selections, correcting selections
but it’s a really good idea to try to make the selection as good as you can first time
round.
And you’ll also probably discover fairly on that feathering can be a really good friend
when it comes to selection because having at least a slightly blurred edge can help
to make even the shakiest selection look a little bit better.
I’m going to go without feather at the moment.
I’ve got the lasso tool selected.
I start somewhere on the edge of the selection.
I’m going to start on its back and I’m going to draw around the edge in a continuous
drawing motion.
Now as I say how good the selection is going to be will totally depend on how steady I
am and me taking my time.
Now I can already see that this isn’t the best selection job I’ve ever done but you
don’t want to sit here for hours watching me do this so let me just do it reasonably
okay but reasonably quickly.
Now as I get towards the end when I join up to where I started I’ll get my marching
ants.
And that’s not bad actually.
Well I don’t think it’s bad anyway.
Sometimes in this situation you may have for instance a gap between an animals legs that
you’ve included in the selection that you want to take out.
Don’t forget the options to subtract from selection and so on I showed you in the preceding
section.
But there is my selection.
If you wanted to see how good that is let me just copy it to the clipboard, let’s
do a new image.
I always find this a really good way of seeing how good a selection is.
That’s not too bad.
I’ve got a little bit of green up there that I don’t want but other than that you
can certainly tell that it’s one horse with a rug on.
So that’s the lasso tool.
I’ve now deselected and I’m going to try the same job again but this time I’m going
to use the Magnetic Lasso.
And the principle of the magnetic lasso is that you move your cursor around the edge
of the object or objects to be selected but you don’t click, you don’t hold it down.
You just follow the edge closely.
And what PSE does is to look for an edge and draw the selection line along the edge.
Now I mentioned just now that one of the reasons we’re doing this selection using the lassos
is because there aren’t distinct edges.
But I think it’s usually a good idea to try this when there is an edge but maybe it’s
not too distinct.
And maybe you just need to give PSE a little bit of help finding an edge.
You can also make this a more successful process by using these slider down here because what
you can do is to set up the first of all the width which is basically the distance from
the cursor that PSE should consider drawing its selection line.
The wider you make that the less it discriminates.
The contrast defines how much of a contrast there needs to be in order to identify an
edge.
And the frequency defines the frequency at which points are added to the path.
Now generally speaking if you’re trying to use the magnetic lasso I find that if you
start using the default settings there you can often adjust those sliders to give you
a more successful result if the defaults don’t really work.
So what I’m going to do here is to start with the horse in the same place.
Note I’m still going to follow around the edge of the horse myself.
I’m going to keep very close to it but I’m not going to click and I’m not going to
worry too much if I deviate away from it certainly by less than 10 pixels.
So I’m going to click to start in roughly the same place.
Note that I don’t need to hold the mouse down.
I don’t need to click.
I just need to follow the edge of the horse.
Now one of the things about the frequency setting is that determines how frequently
PSE puts down those little points that it’s identified on the path.
The more wavy, shaky, moving around a lot the path is the more of those points you need.
But when things go wrong, which they sometimes will, you have to go back a point at a time.
So the more points you’ve got the longer it will take to go back.
So that’s another balancing act.
At the moment looking at this it’s doing a not bad job.
Now let’s suppose that I make a mistake or there’s an indistinct edge and I get
something that’s wrong, like that.
I’ve actually moved away there significantly from the horse’s rug.
What I do is to press the Backspace key and you notice that last point has moved back
one.
Look again carefully.
I’m now back to that point.
I can now get back on track.
I’ve probably got one more point to delete there.
But you basically use the Backspace key to go back to the preceding point, go back to
the last one that was right.
So I’m going to follow carefully around the rest of this.
This is a selection method which I think is very significantly improved once you’ve
used it a few times and you’ve got some practice.
I think you can easily get quite a good feel for this one.
And in my experience it generally works pretty well, particularly when you’ve got quite
complicated edges.
And when I get to my starting point double click and my selection is complete.
And again that’s not bad.
The third lasso tool is the Polygonal Lasso.
And although you can use this on any selection it’s really intended for selections which
are made up of sequences of straight lines.
Now none of these horses are made up of sequences of straight lines but let me just demonstrate
it by selecting one of those fence posts.
I’m going to zoom in first.
It’s not going to be the most interesting thing I’ve ever selected but I can demonstrate
this tool with it.
So I’m going to switch to the Lasso Tools and I’m going to select the Polygonal Lasso.
With this basically I click to start, I then go to the next point and it will draw a straight
line between that start point and the next point that I click.
Same again.
And it basically makes the selection up out of a sequence of straight lines.
And all I need to do to terminate one straight line and start the next one is to click.
I have seen people use this on curved surfaces.
They just do a lot of straight lines.
And it is a particularly easy lasso tool to use.
And as you can see here I can sort of go around a few angles if I really want to.
Now when you’re using this or any of the lasso tools you can end by clicking on the
start point or you can get to a point as I did with the magnetic lasso which was very
close to the start point and double click.
If at any point I double click, I’m going to double click now, PSE takes that as the
end of this particular selection and in this case draws a straight line back to the start
point.
So if I double click here note that’s my selection.
That’s almost certainly not what I intended, but when you get to a point where a straight
line in this case would do to take you back to the start double click will do it.
Otherwise you keep clicking around the edge until you finish making your selection.
That’s the polygonal lasso.
I’ll see you in the
next section.