File size affects image quality

In the past six columns I have discussed different features of the camera. We have covered the camera body, lenses, and flash systems.

In the past six columns I have discussed different features of the camera. We have covered the camera body, lenses, and flash systems. Let’s now focus on the image itself, primarily the type of file, its size, and how the image is stored.

When light enters a camera through its lens, after it bounces off the subject, it is recorded by the computer chip inside the camera. The chip is essentially an image processor that breaks the light into its red, green, and blue components and creates an image from this data. While this might be oversimplified, for purposes of this column, I will leave it at that. Rather, I want to focus more on an economical and efficient method to capture, store, transfer, and display your images as opposed to how they are created.

First, let’s talk about file “type.” Almost every type of digital camera saves an image to “storage media” (Compact Flash Card, Smart Media Card, etc.) as a “jpeg” file type. An image can be recorded and saved as different types of files. A similar analogy is the way a dental crown can be of many types such as gold, porcelain fused to metal, or all porcelain. Likewise, an image file can be either a jpeg, bitmap, tiff, raw, or several other types. The jpeg is the most common. This type of file allows a computer, such as the one in your office or the one inside a digital camera, to compress the image. This reduces its size, by varying amounts, as the image is saved on the storage media. The more an image is compressed, the smaller the image file will be, thereby taking up less space. This allows you to save more images on the same storage media before it fills up and the images have to be downloaded to your computer. Thus, storage media act as reusable film. But compressing a file comes with a cost. While compressing a file allows you to store more photos on given storage media, it also reduces the quality of the images. The files are compressed by removing bits of data from the image. These bits of data are the small details that comprise the quality of the image. So, the more the image is compressed, the less space or “memory” it uses. But the amount of detail in the image decreases as well.

Cameras have different amounts of compression capabilities. The Canon 20D has six levels of compression capabilities, along with raw and combination raw + jpeg settings. The amount of compression is designated as large, medium, or small. This designation refers to the image size, not the amount of compression. Setting the image “quality” to large means that it has little compression, so the image is large in size and the quality is high. Likewise, setting the image to small means the image will have a great deal of compression, so the image size will be small and contain little detail.

A second file type found on the Canon 20D, and others of the latest single lens reflex models, is the raw setting. With this file type, an image has no compression at all. While the files contain all of their detail, they are also quite large. In addition, the raw format is not read by most imaging software. Because of these two factors, I never use this file type. Keep in mind that the American Association of Cosmetic Dentistry now requires a raw format image for accreditation.

So what file size should you use? That depends on just how you want to use your files. A general rule to follow is to use the large setting for printing, the medium setting for lab communication, and the small setting for e-mail and Web use. But these are basic guidelines. I keep my camera set to the largest file size with minimal compression. Those of you who have attended my marketing lectures know that I produce my office art so I do a lot of 13” x 19” prints. These prints are made from portraits taken of my patients, who write testimonials on the portraits. In order to print this size, the image file needs to be very large. Several times I have captured images on the medium setting to save space because I was photographing shade tabs of a patient’s case. But on one occasion after doing this, I went immediately to take portrait photos. I forgot to change the quality setting to large, and did not realize this until after the photo session. But by now, the patient had departed, and I was left with image files that were too small to print at a high quality. Since then, I have just left my cameras on the large setting at all times. I have purchased a 300-gigabyte hard drive for $280, and have increased the memory on my server to 100 gigabytes. So now I won’t have to worry about the size of my images for several years.

Dr. Tony Soileau is a general dentist from Lafayette, La. He has taught digital photography at the Pacific Aesthetic Continuum in San Francisco, the Institute of Oral Art & Design in Tampa, Fla., and the Esthetic Epitome in Charlotte, N.C. He is currently a co-director for the genR8TNext digital photography program. He lectures on the use of digital photography, digital radiography and computerized case presentations, and high-tech marketing. Contact him at (337) 234-3551, or at tony@tonysoileau.com. For more about digital technology, visit www.tonysoileau.com or www.dentalblogs.com.

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