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[ 65 ]size of the map; they affect where the map reaches out to
your image for pixels.The grid example is built so that each square is 128 px,
and it’s done on purpose because D-maps evaluate gray
value as “distance away from zero.” White and black mean
“Go 128 px away, grab a copy of the pixel there, and bring it
back here.” Being in the middle, 50% gray doesn’t go any
distance away; it samples from and copies to right where
it is. When you apply a percentage value in the Displace dia-
log, you’re changing the distance of the sample, but not the
placement. Applying 200% in both vertical and horizontal
directions means a white pixel on the map reaches out 256
pixels down and to the right; 50% pulls from only 64 pixels
away. You can also use negative values, and different values
in each of the horizontal and vertical fields. This example
uses the same map applied at different horizontal values.
It’s important to point out that the values used by the
D-map are fixed pixel values, not scaled, which means that
with larger documents you need to adjust the percent values
to get more displacement. (Note: D-maps only work with
8-bit RGB or Grayscale images. In the following example, my
base image is 8-bit, but if it were 16-bit, I’d have to convert
my D-map to 8-bit before applying it.)
D-MAPS AND CHANNELS
Now there’s one more thing to know before we can really
do some cool stuff. D-maps use channel information, not
just gray values. The Red channel works horizontally, and the
Green channel works vertically. On the Red channel, white
pulls from right to left, and on the Green channel, white pulls Examples of 50, 100, 200, 250, and 300 percent displacement250%
200%
100%
50%
0%
100%
100%
100%
100%
100%
128 px
128 px
128 px
128 px
128 px
200%
200%
200%
200%
200%
256 px
256 px
256 px
256 px
256 px
300%
300%
300%
300%
300%
512 px
512 px
512 px
512 px
512 px