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

[Art_A._...@adobeforums.com]

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 parabola - like this one <http://4.bp.blogspot.com/_BhBX8ycVeL4/SIHhJYmDCgI/AAAAAAAAA-g/2Dc_Tf1Kz5c/s400/400px-Parabola.svg.png> only upside-down; 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, that would look something like this: <http://naturalcureinsomnia.com/img/Bell-Curve.gif>

Can anyone help? Thanks in advance!

[David_E_...@adobeforums.com]

Simple.
go to goggle and type in "make a gaussian curve in ps cs3. There are 3.320 hits to choose from.

Or try this web page. Save and use as a template?

<http://hyperphysics.phy-astr.gsu.edu/HBASE/math/gaufcn.html>

[Art_A._...@adobeforums.com]

Thanks for your reply - I actually googled before posting (with strings similar to what you suggested and with others) and was not able to find a tutorial on drawing gaussian curves with the pen tool. About the template - I'd rather learn to do it with the pen tool, it must be very simple I just don't feel lucky with the pen tool today.

[George...@adobeforums.com]

Art,

Correct me if I'm wrong---I believe you want a schematic Gaussian curve rather than a mathematically precise one.

If so, set up two horizontal guide lines, one running through the desired apex and the other through the curve's baseline. Add three vertical guides, one through the apex and the other two equally spaced on the left and right sides of the guide through the apex.

Let point A be at the intersection of the left vertical with the baseline, point B be the apex, and point C be the intersection of the right vertical with the baseline.

With the pen tool at point A, drag horizontally to the right a fraction of the distance to the central guide. Release the mouse, move the pen tool to point B and drag horizotally to the right about the same distance or until the left half of the curve looks Gaussian. Release the mouse, place the pen tool at point C and drag horizontally rightward until the right half of the Gaussian curve matches the left.

To close the curve, release the mouse and click at a point on the baseline well beyond point C, connect from below with a path of any shape to a point on the baseline well to the left of point A, and then close to point A. Stroke the path, delete the path, and erase all but the Gaussian part.

Experiment with the ABC positions and the drag lengths until you get a decent curve. Should you want a precise curve it would be better to use one of the freeware curve programs out there. But if you want a bit of precision with the pen tool, that's possible by calculating one or two intermediate points between A and B and symmetrically between B and C and then dragging the pen so that curve comes reasonably close to passing through them.

[George...@adobeforums.com]

I should have added that you need not close the path to stroke it. You can leave it as an unclosed path segment by switching to the path selection tool and clicking at any point off the curve.

[Gernot_...@adobeforums.com]

This curve (quoted above) is rather bad:
<http://hyperphysics.phy-astr.gsu.edu/HBASE/math/gaufcn.html>

A corrrect graphic is here. p.19:
<http://www.fho-emden.de/~hoffmann/pstutor22112002.pdf>
It's in fact an EPS program, which can be executed by
Photoshop, InDesign or Illustrator.
Can be used as a template for a Pen Tool graphic.

Best regards --Gernot Hoffmann

[Art_A._...@adobeforums.com]

Thanks a lot for your response. I managed to draw it both using your description and by using an observation that I'd made by myself a long time but which I had forgotten, which is - in order to be able to trace any curved shape with reasonable precision using the pen tool, you need to define as anchor points the points on the curve-to-be-traced that are inflexion points (mathematically, they are the points where the second derivative is zero). It is then just a question of tweaking curve segments between two consecutive APs.

[Art_A._...@adobeforums.com]

I have to say though, George - your method beats the hell out of mine, it is much easier and also the curve looks better since I don't have to worry about making the curve segments unite seamlessly, as it is needed when using the "anchor points in the inflexion points of the curve" method.

[Paulo_...@adobeforums.com]

Gernot,
You sure have created much useful information for PS users. Thanks for the link to this pdf file and others you have posted in recent months.
Are you writing a book?

Paulo

[Gernot_...@adobeforums.com]

Thanks, Paulo,

I'm not writing a book, I'm just trying this & that ...

Best regards --Gernot Hoffmann

[George...@adobeforums.com]

Art

Yeah, just dragging horizontally at three points really is simple. Thank you for the feedback---something which a lot of OPs don't bother with.

Gernot,

Your work is fantastic, as usual. Thanks. I had the same question as Paulo. You have already created many mathematical treatises pertinent to digital imaging which, collectively, would constitute an exquisite, unique, authoritative reference book that some scientific publisher somewhere should drool over and provide assembly and editorial services, freeing you to stay creative.