For many people, the defining characteristic of the shift to digital photography is the ability to review the acquired images immediately after capture. Film camera images were viewable only after development, which was an elaborate and somewhat time-consuming process. If exposure or light settings were incorrect, often the resulting images would be inadequate, which was only discovered after they had been developed. The ability to make changes from shot to shot and verify camera settings for correct exposure has encouraged more people than ever before to use clinical photography in their practices. Despite this advance, misunderstanding the screen settings on digital cameras can lead to errors. This article will attempt to explain how setting the screen of a digital camera from the outset and occasionally checking in on it can help to reduce small systemic errors from occurring.
Digital cameras, as described in some previous Forum photo tips articles, must be set correctly for dental photography to obtain quality photographs. The review screen is very helpful to maintain consistency with these settings, but it is important to remember that each camera is designed as a system of components. There is some variability with components inherent in every system. When using TTL metering, the camera will attempt to expose images to ‘neutral gray’ which in the dental setting can result in underexposed teeth (Fig. 1).
This is avoided when using manual metering, however the photographer is then reliant on the accuracy of the review screen to ensure images are correct. If the screen is naturally brighter or dimmer because of factory variations, it could cause images to be captured that do not reflect the true value, hue, and chroma of the patient.
The most direct way around this problem is to take a series of images with your camera, checking the view screen while at the same time comparing this to a histogram of the image. To summarize the information provided in previous articles: the histogram is a graphical representation of the luminance of each pixel in a given image (Fig. 2). This method of representing an image, from darkest to lightest pixels, can be invaluable in both setting up cameras as well as checking individual components. A picture of a known gray target will show up on a histogram with one very large peak in the center. Varying exposure settings until this is rendered in the middle of the resulting histogram will calibrate the photographs obtained, and then the settings on the view screen can be altered to provide results in line with what the operator feels is comparable to the known gray card brightness (Fig. 3).