The availability of digital cameras has made the telemedicine concept possible but understanding the fundamentals of photography will make the difference between a reliable image suitable for diagnosis and something totally unusable.
With automatic cameras it would seem incredible that photos submitted for diagnosis regularly fall below the standards required for confident assessment.
The most common problems encountered are incorrect exposure and the pictures that are out of focus.
“Under exposure” because of inadequate illumination will present the image as too dark, will give poor detail in the shadow areas, whilst “over exposure”, too much light, will give a very bright picture with no detail in the highlights. The importance of a correctly exposed image when submitting for clinical assessment cannot be over emphasised, the loss of any detail can have serious consequences and any image not achieving these criteria should be rejected.
The other frequently encountered problem is focus, even though most cameras will have a ‘macro’ setting to enable close-ups to be taken, the autofocus sensor can be fooled and frequently seeks out the ‘easiest’ point of focus, locking onto something in the background or foreground of the shot and consequently leaving the main subject out of focus. However, the most common reason for blurred images is simply that the lens is too close to the subject and cannot bring the image to a point of focus.
The amount of light falling on the subject can also have considerable influence over the focus. Using the array of automatic exposure suggestions on some of the gadget laden cameras may appear to be the solution to getting good pictures but this is far from the case when photographing clinical images. The shutter speed selected could be too slow for you to comfortably hold the camera still during the exposure resulting in camera shake where multiple ‘fuzzy’ images are recorded, alternatively if the shutter speed is short enough to prevent this the lens aperture governing how much light enters the camera may be too large and the result will be a partially out of focus image because of a reduced depth of field.
In some dermatological conditions colour can be critical if this is the case special care must be taken to ensure all elements of the telemedicine system from camera and monitor screen used by the photographing clinician are calibrated in the same way as the viewing screen of the reviewing consultant; because this is virtually impossible to achieve in the field, these cases are unsuitable for this type of diagnosis. Despite this, it’s recommended that you set the white balance on your camera to the appropriate setting for the type of light source you’re using whether it is flash, daylight or fluorescent, to ensure visual accuracy.
Although not creating great works of art an element of composition is still required when photographing skin conditions, it’s always a good idea to keep the main feature of your subject central to the frame and where anatomical position could be important always include a locating view to accompany the close-up. Backgrounds should always be plain, neutral in colour, free of clutter and distraction.
Finally, file size seems to present difficulties for many teledermatology users, particularly those within the “choose & book” pilot systems, many providers restrict the size of individual photos to 1Mb, even with the most rudimentary digital camera, achieving this relatively small file size can be a problem with most cameras now routinely producing files between 2 – 5Mb.
Following the suggestion that each set of patient images should include 3 or 4 views together with a patient data file keeping within the total file size of 5Mb is quite a challenge; it will almost certainly mean some form of post processing is required to compress the files to under 1Mb each. There are several free image sizing packages available ranging from Picasa to PIXresizer as well as the paid for Adobe Photoshop Elements. Whichever method you choose by keeping the longest side of the image to 1024 pixels with a resolution of 300ppi and the file size should be around 1Mb.
For more detailed assistance or to express an interest in one of the Medical Photographic Services “Photography for Teledermatology” workshops arranged in a local health centre, please contact us.