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Creating a bell-shapped (Gaussian) curve with the Pen Tool


L

longtalker

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Hello everyone,

I'm trying to create a bell-shaped (Gaussian) curve in Photoshop CS3, using the Pen Tool, however apparently I am not good enough with it... I can create a curve that resembles a simple (upside-down) parabola, however I can't figure out how to further go from here in order to add the extra inflexions on the sides that make the parabola into a Gaussian curve.

Can anyone help? Thanks in advance!
 
It's very simple; learn how to use the pen tool and in your case I would suggest one extra thing; turn on grid, rulers,guides and snap.
 
X-force said:
It's very simple; learn how to use the pen tool and in your case I would suggest one extra thing; turn on grid, rulers,guides and snap.
Click to expand...

I can use the pen tool for basic tasks, this one however escapes me. I know once I've created the first curve I have to add another "degree of modulation" to it by using a combination of Ctrl or Alt plus dragging anchor points.. I will experiment more but if anyone has a quick fix I'd very much appreciate it.
 
I still don't understand the problem...

You can even get a gaussin curve of the net and trace it with the pen tool if that's easier.

And what do you mean with the cryptic comment "I have to add another "degree of modulation" to it by using a combination of Ctrl or Alt plus dragging anchor points"

Now you can wait for others to help you, but trust me, I know "my pen tool" better than most people, my problem is that I simply don't get what the real issue is, it's all too cryptic to me (and probably to many others too).
 
Yes - tracing the gaussian curve with the pen tool is exactly what I want to do, however I cannot go past the first step: I've created a parabola by dragging the second anchor point, but beyond that, any additional anchor points that I create will just give the parabola a far too complex curvature, rather than just bending it slightly in order to produce the gaussian shape.

ANd I meant to say that I know have to use either the Ctrl or the ALt key in combination with dragging one anchor point or another, in order to achieve the desired effect. But then again, I guess the pen tool is all about Ctrl/Alt+dragging...
 
Just add a another point, don't let go of the mouse button and drag, that's how you add a second curve. If you don't like that curve, then just take one of the handles and move them around, stretch them or make them shorter until you have the proper curve. If that doesn't work, then you'll probably need an extra anchor point for that specific curve.

any additional anchor points that I create will just give the parabola a far too complex curvature
Click to expand...

I still don't understand that. What's that "complexity" that you talk about? Are you sure that you have the "paths" icon selected in the option bar and not the "shapes layer" icon (top left of option bar, when you have the pen tool selected).

Otherwise show me a screenshot and upload it to tinypic.com
 
I have used the pen tool quite a bit over the years and don't think I have ever used Ctrl or Alt.

Here is how I would do it ...

Place 3 horizontal guides equadistant apart. Along the middle one, using the Pen tool, place 4 points somewhat equadistant apart. In your tools menu, click and hold down the Pen tool and then select the "Add Anchor Point Tool".

Half way between the first two points you created, click and release. Now click and hold onto the new point you just created. Drag it either straight up or straight down to the respective guide. Repeat this between each of the original points you made alternating directions with each.

Clear as mud?
 
Here's an example:


The pen tool is active, you are not allowed to select any other tool.

Now how are you going to quicky draw this image without using a shortcut key:


oix3y9.jpg
 
You know the old saying, "You learn something new everyday"? It applies to this thread. I am just really getting into "creating" with this program. Mostly I have done retouching of photos and the like. I will look into the pen tool further though. That, you can count on. Thanks!
 
@X-Force: ok, here's what I've been meaning :)

2 APs Pictures, 2 APs Images, 2 APs Photos, 2 APs Videos - Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting -- this is what I get after creating a simple curve (what I've been calling a parabola), using 2 anchor points

3 APs Pictures, 3 APs Images, 3 APs Photos, 3 APs Videos - Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting -- this is what I get after adding a third anchor point to my previous curve; as you can see, it twists the curve in a way that doesn't enable me to mold it into a Gaussian curve.

So where am I wrong & what should I do?
 
66stang66 said:
I have used the pen tool quite a bit over the years and don't think I have ever used Ctrl or Alt.

Here is how I would do it ...

Place 3 horizontal guides equadistant apart. Along the middle one, using the Pen tool, place 4 points somewhat equadistant apart. In your tools menu, click and hold down the Pen tool and then select the "Add Anchor Point Tool".

Half way between the first two points you created, click and release. Now click and hold onto the new point you just created. Drag it either straight up or straight down to the respective guide. Repeat this between each of the original points you made alternating directions with each.

Clear as mud?
Click to expand...

Even less clear... Could I possibly ask you to upload a video of you doing this on youtube or something? In the meantime I'll try some more to follow what you said but it's rather hard to visualize.
 
OK - I managed to do it! All I had to do is define anchor points in the inflexion points of the curve-to-be-traced (i.e. the points where the second derivative is zero) and then tweak the curve segments between two consecutive APs. Thanks again to all who replied.
 
I see you have it figured out.

Going to go ahead and show you what I meant.

001yjb.jpg


002lzm.jpg


003xsp.jpg


004lrv.jpg


Have to click for last one.
http://img13.imageshack.us/img13/7452/005bth.jpg
 
66stang66 said:
You know the old saying, "You learn something new everyday
Click to expand...


Here's the way to do it, study it and it'll save you lots of time with all kinds of shapes, not just this shape. Mind you, I haven't even shown 1/10th of the tricks with Alt and Ctrl.

1182b09.jpg
 
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