Digital Printing Terms Defined
Understanding Digital Print Resolution & Quality
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The best way to understand Resolution & Print Quality is to learn the language:
Ambient Light
The available light completely surrounding a subject that is not introduced artificially.
Aperture
The opening in a camera lens through which light passes; measured in f-stops.
Background
The area behind the subject; it should be smooth, flat, and non-patterned to minimize unwanted reflectance; the background should be plain white or off-white.
Background Illumination
Light that illuminates the background. The background should be uniformly illuminated to remove any shadows or other lighting effects that would otherwise interfere with clearly discerning the facial outline on the background.
Bit
Short for binary digit, which in a computer is the smallest unit of storage.
Brightness
The amount of light and dark areas in an image.
Byte
Short for binary term; a collection of computer bits; on many modern computers, a byte is equal to eight bits.
Cast
See Color Balance, Color Cast & Color Correction.
Centering
The orientation of the facial region within the frame; head should be positioned such that the approximate horizontal mid-points of the mouth and bridge of nose lie on a vertical line at the horizontal center of the photo width; and a horizontal line through the center of the subject’s eyes can be located approximately 55% from the vertical bottom of the photo; and the width of the subject’s head is approximately 50% of the width of the photo.
Color Balance
How a color film reproduces the colors of a scene; using the wrong lighting can cause the colors to appear washed out or unnatural.
Color Cast
The overall bias towards one color in a color image.
Color Correction
Applying filters which help balance the color rendition of a scene to match the color response of the eye.
Composition
The content and organization of the image that is being captured for the photograph. In this context, the composition of the photograph must show a clear, front view and full face of the subject against a plain and neutral light color background.
Continuous-Tone
Refers to an image where like colors in the subject and scene do not change abruptly; the opposite of posterization.
Contrast
The range of difference in the light to dark areas of an image.
Diffuse Lighting
Lighting that is low or moderate in contrast, such as on an overcast day.
Dot
The smallest element that can be printed by a digital printer.
Exposure
In photographic terms is the product of the intensity of light and the time the light is allowed to act on the film, or digital camera sensor. In practical terms, the aperture controls intensity or amount of light and shutter speed controls the time.
Eye Height
The distance from the bottom of a passport or visa photo to a horizontal line going through both eyes and which should measure between 1 inch (25 mm) and 1 3/8 inches (35 mm).
Facial Features
The makeup or appearance of a subject’s face or its parts, including scars, tattoos, etc. Facial Region Illumination
The light that is incident on the subject’s face. The face should be clearly illuminated with all physical features shown and no shadows that would otherwise obscure the facial image.
Facial Region Size
The facial region as measured from the bottom of the chin to the top of the head (including hair) and should be between 1 inch (25 mm) and 1 3/8 inches (35 mm).
File Size
The size of an image in digital photography, measured in kilobytes (KB), megabytes (MB), or gigabytes (GB). File size is proportional to its pixel dimensions; images with more pixels may produce more detail at a given printed size, but they require more disk space to store and are slower to print.
Film
Photographic emulsion coated on a flexible, transparent base that records images or scenes.
Film Speed
The sensitivity of a film to light, indicated by a number such as ISO 100. The higher the number, the more sensitive or faster the film. (ISO stands for International Organization for Standardization)
Filter
Colored piece of glass or other transparent material used over the lens to emphasize, eliminate, or change the color of the entire scene or certain areas within a scene.
Focal Length
The distance between the film and the optical center of the lens when the lens is focused on infinity. The focal length of the lens on most adjustable cameras is marked in millimeters on the lens mount.
Focus
The adjustment of the distance setting on a lens to define the subject sharply.
Focus Range
The range within which a camera is able to focus on the selected subject; i.e., from 4 feet to infinity.
Foreground
The area between the camera and the principal subject.
Graininess
The sand-like or granular appearance of an image. Graininess becomes more pronounced with faster film and the degree of enlargement. In digital imaging, graininess may occur as a result of printing an image, the pixel resolution of which is too coarse, or as a result of using a printer with poor dot resolution.
Grayscale
Term used to describe an image that only contains shades of gray.
Head Orientation
The positioning of the subject’s head, specifically positioning the face to the full frontal position, eyes level and open. For those individuals that wear glasses, proper head orientation is crucial in avoiding unwanted glare from glasses. Even so, care should be taken to meet the required facial area and face centering guidelines outlined in this brochure when positioning the subject’s head to remove the potential glare.
Hue
The attribute of colors that allows them to be designated as red, green, blue, or any intermediate combination of these colors.
Lens
one or more pieces of optical glass or similar material designed to collect and focus rays of light to form a sharp image on the film or digital camera sensor.
Lighting Arrangement
The lighting arrangement for subject illumination which should consist of a minimum of 3 point balanced illumination; two (2) points of illumination should be placed at approximately 45 degrees on either side of the subject’s face, the third point should be placed so as to illuminate the background uniformly.
Natural Expression
The subject’s expression should be natural, with both eyes open. Please refer to the photographs found on this website for acceptable facial expressions.
Negative
The developed film that contains a reversed tone image of the original scene.
Neutral Gray Card
a gray test card without any hue, typically of 18% reflectance.
Neutral White Card
a white test card without any hue, typically of 90% reflectance.
Over-exposure
refers to a condition where too much light reaches the film or digital camera sensor, either because it is too bright or has been applied too long, resulting in a very light photograph.
PPI
short for pixels per inch; the measurement of resolution for displaying or printing digital images.
Pixel
short for picture element; a single picture element of a digital photo or displayed image. Taken together, all of the millions of pixels form a grid that represents the content of the image.
Pixelization
The graininess in an image that results when the pixels are too big, relative to the size of the image.
Positive
The opposite of a negative, an image with the same tonal relationships as those in the original scenes, for example, a finished print.
Posterization
The effect produced when a photographic image is displayed or printed with too few colors or shades of gray; the opposite of continuous-tone.
Refers to an exposed film picture that is printed on photographic paper, in color or black and white. In digital imaging, a print is the result of printing the digital image on photographic-quality paper stock using a digital printer. For passport/visa photographs, the resulting print should measure 2 inches x 2 inches (51 mm x 51 mm).
Printing
Producing the final photo of the captured image which should enable fine facial features to be discernable, whether the print results from conventional photographic processes or digital printout. The resulting print should exhibit a continuous-tone quality regardless of the print method used.
Proper Lighting
The type and position of lighting for both the subject and background so that the subject is clearly illuminated with no shadows on the face or the background.
RGB
The way that the colors are recorded in digital imaging. A large percentage of the visible spectrum can be represented by mixing red, green and blue (RGB) colored light in various proportions and intensities.
Reflectance
The light intensity emitted from a surface in a given direction.
Resolution
Refers to a measure of the detail that can be seen in an image; the higher the resolution, the finer the detail that can be seen.
sRGB
Refers to a standard default RGB color space. This is a device-independent color space designed to remove any color-bias from the representation of an image on the specified device.
Sharpness
Refers to whether an image appears to be in focus.
Subject Pose
The subject’s head, face and shoulders which should be oriented so that the full face frontal view varies no more than ±5 degrees from frontal in every direction.
Subject Positioning
The position of the subject with respect to the camera; the subject should be placed in front of the background such that the focal distance from the camera’s lens to the subject’s face should be no closer than 120 cm.
Tone
Refers to the degree of lightness or darkness in any given area of a photo.
Under-exposure
Refers to a condition where too little light reaches the film or digital camera sensor, either because the light is not sufficient or it hasn’t been applied long enough; it results in a very dark photograph.