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Creating Photoshop Filters, Part 6

All the stuff you forgot from geometry By Dave Nagel
Over the last couple of months, we've covered a broad variety of topics in Photoshop's Filter Factory. Last week we looked at the cnv function as a means of affecting pixels surrounding a target pixel. (Please click the Tutorials button in the left menu to find the previous installments.) This week we're going to take it 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:

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. Now, once you've created your filter, as I showed you in Part 4, your previews will become much more accurate.

It's no secret the Photoshop's Filter Factory is on its last legs. When the next version of Photoshop is released, it will no longer include this utility for making filters, which means that Mac users will no longer be able to make their own filters except through actual programming. Next week we'll have our last installment of this series, and I'll include all of the previous tutorials in one gigantic piece for easier reference.

Dave Nagel is the producer of Creative Mac and Digital Media Designer; host of several World Wide User Groups, including Synthetik Studio Artist, Adobe Photoshop, Adobe InDesign, Adobe LiveMotion, Creative Mac and Digital Media Designer; and executive producer of the Digital Media Net family of publications. You can reach him at [email protected].

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