Understanding Textures & Lighting

Textures and the Lighting Effects filter can make an image jump right off the page or screen. Using a texture to create 3D, however, is a scary thing for most Photoshop users. We'll take some of the mystery out of the process.

Before we get into the nuts and bolts of this week's column, I'd like to take a moment to congratulate Adobe Systems, Inc. on the successful release of Photoshop 6. The product has started arriving and is being put into production. And, judging from the nature of the requests for assistance I've received, the transition is going smoothly for most. (The problems that have arisen are, almost exclusively, user inexperience or hardware issues.)

I jokingly pointed out to a colleague recently that Photoshop has a specific learning pattern for most users:

• Get scared of the Pen tool. Learn to use the Pen tool.
• Get scared of Levels. Learn to use Levels.
• Get scared of Masks. Learn to use Masks.
• Get scared of Curves. Learn to use Curves.
• Get scared of Color Management. Stay scared of Color Management.
• Get scared of Channels. Learn to use Channels.
• Get scared of Textures. Learn to use Textures. In this column, we'll try to start the process of getting un-scared of Textures, just in time for Halloween.

Textures are grayscale images that can be used by certain features in Photoshop to represent 3D (among other functions). The primary employer of Textures as 3D in this manner is Lighting Effects (Filter> Render> Lighting Effects...). This filter uses variations in color to represent variations in "elevation" of an image. We'll use the analogy of elevation, such as that in a relief map, throughout this discussion.

Think of land, in reality and as represented on a map, as consisting of points above ground level (hills and mountains, primarily) and points below ground level (valleys, bottoms of lakes and oceans, riverbeds). If we think globally, we can think of "sea level" as the average, with mountains being higher and oceans being lower. This leads to the key relationship among grayscale colors in a texture:

• "Sea Level," ground zero, is a grayscale value of 128.
• "Mountains," areas above sea level, range from 129 to 255.
• "Oceans," areas below sea level, range from 127 to 0.
• The farther the gray of an area if from 128, the more extreme the "elevation."

Figure 1 shows a texture image set up to demonstrate how this works. The background is neutral gray, with an RGB value of 128/128/128. The triangles and their labels were also colored using RGB values. Each of the three component colors was set to the value shown to create the appropriate shade of gray. For example, the triangle labeled 170 has a color value of R-170/G-170/B-170. Using the grayscale slider in the Color Palette, this is equivalent to 40%. (Note that 50% gray using the slider has an RGB value of 147/147/147.) The triangles on the right are white and black, with respective values of 255/255/255 and 0/0/0. The gradated image has a standard black-to-white gradient.

To the far left are the first triangles in the series. On top is a triangle (and label) filled with a gray value of 130. This is difficult to see because the background is 128 gray. The 2-point variation is virtually imperceptible. Below is a barely-visible triangle and label with values of 125. The 3-point difference can be picked up by the human eye.

To prepare this image for use as a texture, it must first be flattened and saved as a grayscale psd file. Images in other color modes cannot be used. To use a texture with the Lighting Effects filter, it must appear in the target image as an Alpha channel (a mask).

• Open the target image.
• Open the grayscale texture file.
• Open the texture file's Channels palette.
• Drag the only channel available from the texture image onto the target image and release.
• The channel appears in the Channels palette of the target image as Alpha Channel, and it active and visible. Figures 2 through 4 show the progression.

Dragging the Gray channel.

After the channel is dropped, it become active and visible.

Click on the RGB channel to make the composite visible and de-activate the Alpha channel.

The target image in this case consists of an RGB image filled with red (255/0/0). We'll use the simple red fill to show the changes in "elevation." Figure 5 shows the settings that were used. Note that the channel Alpha 1 must be loaded in the lower part of the dialog box. Figure 6 shows the result.

Observe how the shadow and highlight effects on the pairs up and down triangles are of virtually the same magnitude, and are reversed. With the settings shown in Figure 5, the left-most triangles and labels are now visible. However, there are virtually no differences among the effect at the more extreme "elevations." Looking at the gradated shape, you can see that past about the halfway mark in each direction the effect becomes uniform.

To see more clearly how changes in gray values can produce different "elevations," the filter was undone and re-applied. The only change that was made was a reduction in the Flat/Mountainous slider from 76 to 2. (The slider can be seen at the bottom of Figure 5.)

Textures in the form of images can also be applied using Filter> Texture> Texturizer. The dialog box is shown in Figure 8, and the result in Figure 9.

Texturizer doesn't require that the texture map be an Alpha channel within the image. Rather, the Load Texture button allows you access to any .psd image. Results are far more predictable with grayscale, but color images can also be used as textures with the Texturizer.

Part 2 of this two-part series will look at using textures and the Lighting Effects filter with photographic images.

Six Shooters

When upgrading to Photoshop 6, if the installer asks for the CD of your previous version, look for the Eject button.

There have been a couple of reports of conflicts with ATI All-in-Wonder video cards. At least one successful resolution of conflict came by setting the card to 28 bpp.

The Photoshop Preference menu has moved. You'll now find it under Edit, rather than 5.5's location under the File menu.

For Mac users, the preferences file has also moved. It's back in the System folder, inside the Preferences folder.