bright light triggering the pupil to contract. (This should not be confused with some autofocus assist beams, which use a series of flashes for focus instead.) Having the subject look away from the camera lens. Increase the lighting in the room so that the subject's pupils are more constricted. If direct flash must be used, a good rule of thumb is to separate the flash from the lens by 1/20 of the distance of the camera to the subject. For example, if the subject is 2 meters (6 feet) away, the flash head should be at least 10 cm (4 inches) away from the lens. Professional photographers prefer to use ambient light or indirect flash, as the red-eye reduction system does not always prevent red eyes — for example, if people look away during the pre-flash. In addition, people do not look natural with small pupils, direct lighting from close to the camera lens is considered to produce unflattering photographs, and pre-flashes can be distracting or annoying. Red-eye removal is built into many popular consumer graphics editing software packages, or is supported through red-eye reduction plug-ins; examples include Adobe Lightroom, Adobe Photoshop, Apple iPhoto, Corel Photo-Paint, GIMP, Google Picasa, Paint.NET and Microsoft Windows Photo Gallery. Some can automatically find eyes in the image and perform color correction, and can apply it to many photos at once. Others may require the operator to manually select the regions of the pupils to which correction is to be applied. When performed manually, correction may consist of simply converting the red area of pupils to grayscale (desaturating), leaving surface reflections and highlights intact. As a medical warning sign In a photograph of a child's face, if there is red-eye in one eye but not the other, it may be leukocoria, which may be caused by the cancer retinoblastoma. The child's eyes should be examined by a general physician. References Eye Science of photography