(Note: If you're unfamiliar with User Defined Filters (UDFs), then please take a look at UDF Basics before working through this tutorial.)
In other UDF tutorial here we looked at the basic rules of thumb for making UDFs, and we made some blur filters, sharpen filters, and edge filters. In this tutorial, we'll make a couple embossing filters.
With the blur filters, you added to the UDF matrix positive peripheral cell values around a positive central value. For a sharpening filter, you also use a positive central value, but with negative values surrounding the central cell. For edge filters, the central value is what's negative, with positive surrounding values.
Here's our rule of thumb for Embossing filters:
For an Embossing filter, use a positive center value and surround it in a symmetrical pattern of negative values on one side and positive values on the other.
To create your first emboss filter, choose Effects > User Defined Filters, then fill in the matrix like this:
(Note: The filter's preview windows have been turned off here.)
Remember that in general you maintain the overall brightness of your original image by using values in the matrix that sum to 1. Here we have a central value of 1, with four surrounding cells filled with 1 and four surrounding cells filled with -1, for a sum of 1.
Applying this filter gives this result:
The embossing effect here is quite extreme, but don't forget another rule of thumb mentioned in UDF Basics:
Lessen the effect of a filter by increasing the value in the center cell; compensate with the appropriate Divisor to maintain the brightness of the original image.
Let's give it a try. We'll modify our original embossing filter this way:
We've increased the central value from 1 to 3. The sum of the matrix values now is 3, since we have a central value of 3 and four surrounding cells filled with 1 and another four filled with -1. To adjust this sum to get 1, press the Compute button to set the Divisor to 3.
Here's the result this time:
You can adjust the direction of the embossing by repositioning the positive and negative cells that surround the center cell. For example, the values below produce the results that follow:
Experiment with your own selected values. You're sure to come up with some interesting embossed effects!
Note: If you'd prefer to get unsaturated results rather than full color embossing, choose Grey Values in the Apply To pane of the User Defined Filters dialog.
Copyright ©2003 Lori J. Davis
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