Digital Image Processing for Lighting Design Tutorial 1: Introduction 1998 02 16

The second stage in creating a lighting design, after characterizing requirements and constraints, is visualizing the intended effects. Programs such as Lightscape may be excessively cumbersome for this purpose, given the amount of time required to define, debug, and process a lighting model. Manual graphic techniques are a quicker, though less accurate, approach to exploring lighting effects. Digital image processing has raised new possibilities for exploring lighting possibilities. This tutorial will take you through some effects that can be studied using Photoshop.

The version of Photoshop used in this tutorial is version 3, available in the Mac lab. When time permits, it will be updated to account for characteristics of version 4 (Wintel lab).

The sample file is "cafe-light" and may be found on xxx Copy file "cafe-light" to the working directory that you have established on your share of the system drive or to the scratch area on the computer on which you are working (note that, in the latter case, the file will only be available on and saved on the local hard drive).

Launch Photoshop and open "cafe-light" in the directory in which you have copied it.

Photoshop is a very powerful tool for editing images. Photoshop treats files in "bit mapped" format. This can be understood by comparison with "vector" format. In vector format (the format used for data in CAD packages such as AutoCAD), lines are represented as pairs of points in space with a connection between them. In a three-dimensional view, the lines are projected onto the two-dimensional surface of the computer screen. In bit map format (such as the "cafe-light" image), an image is only a two-dimensional image represented by all the points of which it is comprised. If an image is black and white, it will be made up of points that are either black or white. Points in a gray-scale image, may have different shades of gray assigned to them (this takes more memory). Points in a color image may have extensive color properties and the amount of memory required to add all this information represents an exponential increase in memory demand from gray-scale.

Part I - Verifying that the Lighting Effects Options are Loaded

You must first verify that the "Lighting Effects" filters are available.

1. From the menus, select "Filter-Render;" if "Lighting Effects" appears as an option, skip to Part II.

2. To load the "Plug-in" that provides "Lighting Effects," select "File-Preferences-Plugins..." A "Select the plug-ins folder" dialogue box appears.

3. Use the selection box to locate the folder "Lighting Styles" (it should be in Adobe Photoshop 3.0/Plug-ins/Filters). Highlight it and click on "Select `Lighting Styles'."

4. You must quit and re-start Photoshop for the plug-in to be come active (you do not have to restart the computer).

Part II - Basics of Lighting Effects

1. From the menus, select "Filter-Render-Lighting Effects" - a "Lighting Effects" dialogue box appears. Note the preview window in which icons representing light sources are shown and corresponding effects are previewed.

2. Under "Light Type," note that three types of lights are available" spotlight, directional, and omni.

   The spotlight casts an elliptical beam of light.

   The directional light is a remote source like the sun .

   The omni light shines in all directions directly above the image.

3. Select "Spotlight" and click "OK" - the image grows darker, except on the right side of the table.

   Note that two options (sliding scales) are available in the "Light Type" selection area. One is for intensity (it is possible to set a negative intensity, removing light, an effect not available with real light sources). The other scale, applicable only to spotlights, is a focus option, ranging from narrow to wide (i.e., spot to flood).

4. Select "Spotlight" and click "OK" - the image grows darker, except on the right side of the table.

5. Select "Lighting Effects" again. The white circle in the preview represents the light source; drag it until it is above the right most table. The line running form the light sets its direction and the "handles" (gray squares on the surrounding ellipse) set the boundaries of the illuminated area. Drag the "handle" (gray square) with the line connecting to the white circle until it is below the table (you may place it outside the preview image). The preview will reflect this change. Click OK to view the fully processed image.

Part III - Adding a Light Source

1. From the menus, select "Filter-Render-Lighting Effects".

2. Add a second light source by clicking on the lamp icon below the preview box and dragging it into the preview image (position it above the second table from the right).

3. To make it easier to work with the second source, click on the first light source to select it and click on the "On" box to "turn off" the first light.

4. Adjust the properties of the second light to suit yourself.

5. Click on the first light source to select it and click on the "On" box to "turn on" the first light.

6. Click OK to view the fully processed image.

These variations should give you an idea of the possibilities of digital image processing for conceptual development of lighting design. It is much quicker than radiosity-ray tracing analysis. You can use rendered images from CAD software (e.g., Form-z) to work on a particular setting or from photographs of an existing building (e.g., to redo exterior lighting effects).

Part IV - Omni and Directional Lights; Light Color

1. From the menus, select "Filter-Render-Lighting Effects".

2. To make it easier to work, click on the second light source to select it and click on the "On" box to "turn off" the second light.

3. Change "Light Type" to "Omni." The circle around the source, adjustable by manipulating the handles, defines the area of the effect. Experiment with the omni light (it would be wise to save the file and use a copy at this point, so that you can return to the starting point after experimenting).

4. If necessary, open the file you saved at the beginning of step 3. Change "Light Type" to "Directional". Rotating the line form the circle will change the direction of the light. The length of the line determines the height of the source above the image. A shorter line results in a brighter effect.

5. The color of the light source may be adjusted by clicking on the square to the right of the sliding scales for focus and intensity. The Apple Color Picker will appear. Clicking in the square will change the color settings.

Part V - Lighting Effects and Textures

In the properties area, four options are available. "Gloss" varies the effect of the surface from diffuse (matte) to specular (shiny) reflections. "Material" determines whether the light source or the object has greater weight in determining the color of the reflected light. "Exposure" lightens or darkens the light (negative subtracts light!). "Ambience" determines the extent to which the light appears to be combined with other sources (e.g., as if there were daylight in the space); A value of 100 means that only the light source will be used, -100 means that the light source will have no effect.

Predefined textures may be added by placing a texture in the "alpha" channel of the Photoshop file (it must be the same size as the image being processed). Choosing texture channels will then add "bumpiness" to the surface.

Part VI - Styles

1. From the menus, select "Filter-Render-Lighting Effects".

2. In the "Styles" area, select "Five Lights Down" this creates the effect of five spots.

3. Experiment by selecting other styles. Note that you may create and store your own arrangement by using "Save..." in the "Style" area.