Correcting color temperature and parallax
» From marketing materials to presentations, reports, and websites, digital images are an increasingly essential part of doing business, and the lighting industry is no exception. Yet, because of its rapid development and technical complexity, many pass up the opportunity to take full advantage of the technology. Whether photographing a prospective job site or recently completed work, a designer needs to be able to use a digital camera competently under a wide range of light conditions. And then, whether using a photo for marketing purposes, or to illustrate a proposed lighting scheme, that designer should also learn to manage and edit images. Here are a few basics for those developing these skills.
Meet the Megapixel
Digital images and cameras are rated in megapixels. A pixel is a dot, and in the printing world, picture quality is determined by the number of dots per inch (dpi): simply, the more pixels, the better. Magazine-quality printing requires a resolution of at least 300 dpi in both horizontal and vertical directions. So, for example, a standard 3x5 (3 inches by 5 inches) printed image requires (3x300) x (5x300) dots, or 1,350,000 pixels (1.35 megapixels). An 8x10 print demands 7.2 megapixels. If the original image has fewer pixels than needed, photo-editing software can attempt to fill in the missing dots, but the resulting picture will lack sharpness and detail.
However, most other uses of digital images require fewer pixels than typical digital photos record. For example, a full-page image on the average 1024x768-resolution computer screen or portable video projector only requires 0.8 megapixels. Even the most stunning professional-grade video monitors and projectors require little over 4 megapixels. This suggests that for most practical uses, images over 4 megapixels are only necessary when 5x8 prints or larger are needed. And for many everyday uses, images of 1.6 megapixels or less are fine.
Each pixel has specific color and brightness qualities. Data for an individual pixel is contained in approximately 4 bytes of memory; so, for every megapixel, it takes about 4 megabytes of storage to retain the original image information. This 'raw' data can be stored in one of several original file formats, the most common called 'tagged image file format' or TIFF (.tif). Raw image files are often large, requiring a lot of storage space and transmission time when downloading from websites or e-mailing.
The solution is either to reduce the picture's total number of pixels, or to make the data set smaller by compression. Compression keeps the number of pixels the same, but carefully throws away unnecessary or redundant data. The most common compression method, called 'joint photographic experts group' or JPEG (.jpg), creates files with varying levels of compression, from level 12 (minimum compression) to level 0 (maximum compression). Remember, compression permanently removes data in a careful and hard-to-notice way, but the greater the compression, the lower the final image quality. And once gone, you can't put it back.
Formatting a photo for the web usually requires both making the picture smaller and using compression. For instance, imagine designing a web page with text, pictures, and other graphics. You have an original 4-megapixel photograph in TIFF format. But you only plan to fill a quarter of a 1024x768-resolution computer screen. In this case, the picture will be (1024x768)/4, or about 196,000 pixels. Even at this size, a TIFF file will require about 800KB of data-much too large for ordinary web use. So that websites download efficiently, it's best to use photo files that are no larger than about 50KB. JPEG compression level 3 will reduce this 0.2 megapixel file to about 49KB of memory.
Get the Picture
Digital cameras continue to become more powerful and less expensive. The most unique requirement for interior lighting-related photography, however, is not a common amenity: an extra-wide-angle lens. As a simple rule, the camera should have the equivalent of a 24mm (or less) wide-angle lens (based on a 35mm camera). Not many cameras have this ability without a lens attachment or, in the case of a digital SLR, a special wide-angle lens that attaches to the camera body. A camera for less than $500 will meet most needs; but it is often said that the lens makes the picture, so to publish or compete with photos, a better camera is a requisite investment. Expect to spend at least $1,000 on a digital SLR with a truly great lens, keeping in mind that a top professional camera and lens system can easily cost over $30,000.
Generally avoid the flash in favor of long exposures, which means using a tripod. There are several easily portable pocket tripods and camera clamps. The flash can be used for casual photos and job-site records, but its color temperature-usually 5000K to 7500K-will normally be different than the interior lighting, and combined with the tendency to overlight foreground images, flash photos are not good at illustrating architectural lighting.
Digital cameras shoot light well because they are relatively insensitive to differing sources. The photographer can mix halogen and 3000K fluorescents in the same photo without worrying about the camera recording subtle differences in color temperature. In addition, the camera can automatically adjust to match the color of the lamps in the space. However, if two significantly different Kelvin sources are present, the digital camera must be set for a single color temperature (an advanced feature most cameras offer) and sources of other temperatures will stand out. Designers shooting two sources together, such as electric light and daylight, must either accept the result, or shoot multiple exposures and stitch the pictures together later with the proper color temperature for each.
The key to a great image is composition. Emphasize perspective by taking pictures from the corner of a room rather than the middle. Also be careful with the foreground: make sure there is something there! Often a photograph shows a big empty-and boring-floor. And take camera height (point of view) into account, as a lower camera position can make a room look taller and vice versa.
Digital photos are easily cropped and, if necessary, rotated. For example, adjustments to the perspective (parallax) are often made after the fact. Unless taken with a very expensive camera and lens, any photograph of a structure-especially through a wide-angle lens-will exhibit bending or arcing lines.
Manage the Picture
Most cameras and scanners are bundled with an image-editing program that will suit the casual user. The best-known, Adobe Photoshop, is relatively expensive, but those willing to buy and take the time to learn it will have developed an important professional skill. Even professional photographers are making the switch from film, as pixel count can now be high enough for crisp photos in all but the largest formats. No longer are sophisticated lenses with bellows and tilt-and-shift capabilities needed, either. Every common problem-including cropping, straightening the view, correcting for parallax, correcting for color temperature and saturation, and adjusting the brightness and contrast-can be fixed by software. In the hands of a skilled photo editor, major surgery can be performed.
Image Editing as Practice
Digital image editing and management are critical new skills for the lighting designer. Using photo-editing programs, a designer can create simple illustrations of complex visual scenes, especially photos of existing buildings, without actual rendering software. Also, using photo-editing techniques, one can take a line drawing or rendering and artistically add lighting effects to illustrate a concept for a fraction of the cost of creating a computer-generated lighting rendering.
In one example, illustrated above, the architect developed drawings of the proposed building for community planning and architectural review groups. The community also required that the exterior lighting be described, well before actual schematic design had started. Using image-editing software, and working from the architect's line drawings, we created a 'rendering' of the façade lighting. At relatively low cost, a compelling image was generated, and the project, including the proposed lighting concept, was granted approval to proceed.
Using these programs, a designer can also add 'new' lighting to existing photos. It is often not practical to digitize a space with complex detailing, especially when developing quick concepts to gain schematic approval. Once again, a skilled editor can create realistic images that suit the need of the project for a modest cost in professional time. It is for situations like these that, when reviewing resumes, I now look for photo-imaging skills in employee candidates. james benya
James Benya is a professional lighting designer and principal of Benya Lighting Design in West Linn, Oregon. He is editor-at-large for A|L. This article was adapted from a program presented by the author at the January 2005 IALD Annual Meeting.