| The Complete Guide to Creating Photoshop Filters |
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Part 3: Geometric Expressions
Now we'll take things a little bit further with the addition of new functions to our expressions. You can throw on top of these expressions several more functions to make things behave a bit differently. By simply trying out sine, cosine and tangent (abbreviated sin, cos and tan in the Filter Factory), you can generate some wild effects. Again, we're simply going to build upon the expressions we created in the previous section. You can do this in one of several ways. First, you can simply enclose the whole expression inside the parentheses in the expression sin(). So the example for the R channel above would look like this: [an error occurred while processing this directive] sin(src(cnv(ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(6)), cnv(ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(7)),0))
Remember the extra parentheses at the beginning and end. Now, I don't particularly like the way this makes the image look. So the other way you can do this is to take your expression and insert sin (or cos or tan) functions throughout it. We could do it:
src(sin(cnv(ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(6))), sin(cnv(ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(7))),0)
or we could place the functions randomly throughout the expression, remembering to use parentheses properly, as in:
src(cnv(sin(ctl(0)),cos(ctl(0)),tan(ctl(0)),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(0),ctl(6)), cnv(ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(1),ctl(7)),0)
You can see examples of the effects below.
The original image
Three ways to apply a sin function to a convolve function.
One important thing to keep in mind is that the Filter Factory preview is not too terribly likely to represent the final look of your image. You might see some great banding and noise effects in the preview, only to come up with flat posterization when you apply the filter. There's really no way to say when it's going to be accurate, so you'll need a little extra patience to get just the right look.
Part 1: Introduction to Basic Operations in Filter Factory
Part 2: Convolving Pixels
Part 3: Geometric Expressions
Part 4: Conditional Statements
Appendix 1: 3D Effects in the Filter Factory
Appendix 2: More on 3D Effects
Appendix 3: Customizing Your Filter Interface
Complete: The Whole Thing on One Giant Page!
Further Resources: I've tried to make this series as accessible as possible for you folks without any programming background. If you'd like to take the Filter Factory even further or just learn more about the guts of Photoshop, there is a highly technical instructional document that you can find at http://www.thepluginsite.com/knowhow/ffpg/ffpg.htm. I highly recommend it. For me, it's been a great source for experimentation, even if, at first, I didn't understand everything that the author was talking about.
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