GLOSSARY
The following glossary attempts to simplify complex terms into simple to understand language. For more detailed explanations, many great books on photography are available as well as websites galor that have photography glossaries. This glossary is currently under construction and more entires will be added soon.
Ambient light – The “natural” light in a scene. Explanation: Shooting outdoors in sunlight without a flash is shooting in “Ambient light.” Shooting indoors with a person seated near a window letting in sun light from outside is shooting in ambient light. Shooting indoors without a flash (but with just the room lights turned on) is called shooting with Ambient light” (the room light is the room’s “natural” light and therefore is the ambient light). Bringing in a light source such as a softbox, light stand, or flash to brighten the “natural” scene is NOT using Ambient light. A photo may contain ambient light (light that was naturally there) and external lighting (light that was added) in the same photo. And example would be indoor photography. Much of the photo may be lit by the room’s ambient light but the flash will light up your primary subject with more or brighter light.
Aperture – A small, circular opening inside the lens that can change in diameter to control the amount of light reaching the camera's sensor as a picture is taken. The aperture diameter is expressed in f-stops; the lower the number, the larger the aperture. For instance, the aperture opening when set to f/2.8 is larger than at f/8. The aperture and shutter speed together control the total amount of light reaching the sensor. A larger aperture passes more light through to the sensor. Many cameras have an aperture priority mode that allows you to adjust the aperture to your own liking. See also shutter speed. The wider the aperture (lower the f-number), the faster the shutter speed will need to be in order to avoid over-exposing the photo. The smaller the aperture (higher f-number) the longer the shutter will need to be open to allow enough light in to correctly expose the photo. Photographers can use aperture to control a photos “Depth of Field” (see Depth of Field).
Artifact(s) - Distortions or excess noise (see noise) which are caused by the sensor, the optical system or image processing (such as compression). Explanation: When a digital image is taken and compressed into say a jpg compressed format, small “artifacts” which appear like little dots of light or other jagged edges around objects can appear in the photo which reduce the quality of the image. Software such as Photoshop is designed to help reduce and remove artifacts in photos. In general, the smaller a camera’s sensor is, the more likely you are to see artifacts appear. Many point and shoot cameras have a tiny sensor (5-8mm) while most dslr’s have a much larger sensor (23mm) and “Full Frame” dslr cameras are equivalent to 35mm film cameras (35mm censor size).
Aspect Ratio - The ratio between the width and height of an image or image sensor. Explanation: Many point and shoot cameras capture a 4:3 aspect ratio (designed to fit nicely on a full standard shaped computer monitor when blown up) while most dslr’s capture a 3:2 aspect ratio (designed to fill a typical 4x6 print as typically seen in film processing when blown up). You can increase the size of the image from the sensor, to make a print for example, but you may have to crop the photo to fit the print size you wish to make if the print has a different aspect ratio than the image you captured. For example, a camera that captures a 4:3 aspect ratio will not make a perfect 4x6” print at Costco. Imagine for a moment that 4:3 means the image is 4 inches by 3 inches in size (that’s a 4:3 aspect ratio). To make a 4x6 print we need to increase both sides by a factor of 1.5. If we take 4” x 1.5 we have the perfect long dimension (6 inches) but if we take the other dimension of 3” x 1.5 we get 4.5.” Ut oh! Now our image will get chopped off if we make a 4x6 print. We’ll lose a half an inch of the photo. If you take your photo to a printer like Costco, the lab is going to have to make a decision for you on what half inch of the photo they are going to cut off in order to make a full 4x6 print or they will have to shrink it down a little so the full image will fit on the 4x6 paper but not all of the paper will be filled. The same sort of problem occurs when someone takes a photo shot with a 3:2 aspect ratio and wants to make an 8x10” photo. A 3:2 aspect ratio will make a perfect 4x6” print by multiplying by a factor of 2 (i.e. 3” x 2 = 6” and 2” x 2 = 4”, so a perfect 4x6 size), but if we make an 8x10 the aspect ratio is actually 5:4 (not 3:2) and something will get cut off if we blow it up to this ratio.
Automatic Exposure - A feature where the camera automatically adjusts the aperture or shutter speed or both for the proper exposure. Set in “Auto,” your digital camera will pick the correct combination of aperture and shutter speed for you in order to capture a correctly exposed photo.
Bracketing – Tells your camera to take several exposures, some greater and some less than the suggested exposure that it calculated to be corrected. Bracketing allows for error and permits selection of the best exposure after development. Explanation: In some shooting conditions the light can be tricky. Will the camera expose the photo for the bright sky for example? If so, the foreground may come out very dark with no detail in the shadows. But if your camera exposes for the darker foreground, the bright sky might appear FAR too bright in the image and you will lose all detail in the clouds? Exposure bracketing tells your camera that you want to purposefully underexpose and/or overexpose some of the photos in a series of shots so you can increase your chances that one of the exposures will get it “just right.” Exposure bracketing is also a good way to create High Dynamic Range photos where the correctly exposed parts of one photo are merged with the correctly exposed parts of another photo to create a photo that appears correctly exposed through the entire image even though the camera could not capture it with one capture.
Buffer - A temporary storage area usually held in Random Access Memory and used as a temporary holding area for data. Explanation: After a picture is taken with a digital camera, the data is saved to a storage device inside the camera (like a Compact Flash Card) so you can retrieve the image later. Writing to storage devices can be a “slow” process so cameras add a “Buffer” where an image is temporarily stored in a much faster data storage area and then written to the storage device once the buffer is full. Because the buffer is so much faster than writing directly to a storage device, a camera can “burst” a series of photos very quickly before it needs to start writing data to the storage device. When the buffer is full, the burst will potentially slow down as it no longer has a place to store photos in its quick access memory. Higher-end cameras have larger buffers allowing for a longer and faster burst of photos before the camera starts to slow down. In addition, high speed storage devices can be purchased which decrease the amount of time needed to write to the storage device. Many cameras on the market today can burst at a rate of around 3 frames per second for a certain period (say up to 10 shots). Mid level dslrs tend to burst at a rate of around 5 frames per second and with high speed storage cards can sustain that burst rate until the card is full. High end (professional) cameras tend to burst around 10 or more frames per second and can continue that rate until the storage device is full. For comparison, a video recorder captures frames at a rate of about 30 frames per second.
Burning – Selectively darkening part of a photo with an image editing program like Photoshop Elements. Photographers often use this technique to darken shadows in clouds to make them more dramatic and ominous looking. The effect is often paired with “dodging” (brightening) the light areas as well. The process of using these editing tools to selectively darken shadows and brighten highlights is called “Dodge and Burn.”
Burst - The ability to rapidly capture images as long as the shutter button is held down. Many cameras on the market today can burst at a rate of around 3 frames per second for a certain period (say up to 10 shots). Mid level dslrs tend to burst at a rate of around 5 frames per second and with high speed storage cards can sustain that burst rate until the memory card is full. High end (professional) cameras tend to burst around 10 or more frames per second and can continue that rate until the storage device is full. For comparison, a video recorder captures frames at a rate of about 30 frames per second.(See Buffer for more information on Burst).
Capture - A term used in digital imaging meaning "to photograph". The term is used to differentiate the method by which the image is made. As the word "photograph" is closely associated to film photography, "capturing" is applied to specify a digital sensor is used." In TCDPC presentations you may often hear the terms “photo” and “capture” used interchangeably.
CCD - (Charge-coupled device) An image sensor that reads the charges from the sensor's photosites one row at a time. This is the standard sensor type in most point and shoot and entry level dslr’s. Higher end digital cameras employ a different type of sensor that is faster and captures more data.
Clipping - The removal of some portion of an input signal or quantity from the resulting output, generally by setting certain low and high thresholds and discarding the data that falls below the low threshold or above the high. Explanation: Photo editing programs like Photoshop Elements 6.0 allow you to easily see areas of a photo that are losing detail either by making the photo too bright or too dark. When set in the correct mode, a photographer may brighten an entire image in PhotoShop and look for small dots to appear in the image which are flashing a bright color. The flashing color indicates to the photographer areas of the photo that are being “clipped.” Clipping means that those area’s of the photo have now become so bright that all of the shadow detail in that area is completely gone and it is pure white. The same thing can be done with darkening the photo and the software will flash areas of the image that are being “clipped” in the dark areas (meaning they have turned pure black). Typically a photographer would like to retain detail in the brightest and darkest parts of the photo but they may be ok with some clipping of the detail in areas where it really isn’t important to see detail anyway.
Cloning - To make an exact duplicate of digital image data. In digital systems it is possible to copy part of an image onto another. Explanation: Cloning is an editing tool that is most often used to duplicate an object or to remove an object from a photo. For example, a person could use the clone tool to fill a sky with hot air balloons by simply cloning one balloon over and over again so it appears there were more balloons in the sky than there originally were. Cloning is also used to remove objects such as an annoying telephone pole against a blue sky. The blue sky can be cloned over the telephone pole thereby effectively erasing the telephone pole and giving the illusion that the pole was never there. In TCDPC contests, cloning is usually only allowed in Advanced Editing rules to remove minor distractions (like telephone poles) from the photo rather than to duplicate and add objects not originally captured (like the balloon being cloned over and over in the above example).
CMOS - (Complementary Metal Oxide Semiconductor) An imaging system used by digital cameras. Considered a step up from CCD sensors.
Color Balance - The accuracy with which the colors in the image match those in the original scene. Digital cameras can easily be set to “shift” the colors in a photo toward one color or another. In the film days, photographers might apply an orange filter to the front of their lens to shift all the colors toward oranges. A correct color balance equally processes red, green, and blue. If the colors do not appear correctly we say that the color balance is off.
Color Depth - The number of bits assigned to each pixel in the image and the number of colors that can be created from those bits. True Color uses 24 bits per pixel to render 16 million colors.
Composition - The arrangement of the elements within a photograph--the main subject, the foreground and background, and supporting objects. At TCDPC we strive to teach pleasing compositions and to avoid common photography “mistakes” such as centering all of your subjects dead center of the photo. One form of composition that is talked about a lot at TCDPC is the Rule of Thirds which asks you to imagine a photograph divided into thirds horizontally and vertically and then trying to position your main subject of the photo on one of the intersections of the thirds lines. This generally provides a much more pleasing composition.
Contrast - A measure of rate of change of brightness in an image. Contrast is particularly important in black and white photography where a full range of blacks to whites with varying shades of gray in between are desired. Adding a little contrast to an image (making the shadows darker and the highlights brighter), often times improves an image dramatically.
Crop (cropping) - To trim the edges of an image, often to improve the composition. Cropping can also be used to change the Aspect Ratio of a photo from say 4x6 to an 8x10 ratio (see Aspect Ratio). Photographers often crop images to make the composition of the photo better or to crop out distractions on the outer edges of a photo.
Depth of Field - The distance between the nearest and farthest points that appear in acceptably sharp focus in a photograph. Depth of field varies with lens aperture, focal length, and camera-to-subject distance. Photographers use Depth of Field to create pleasing effects such as a portrait of a person up close where the background is soft and out of focus or landscapes where everything from the forground to the background is in sharp, crisp focus. As a general rule, wide open apertures (small f stop number) will produce a “shallow” depth of field and small apertures (large f stop number) will produce a “long” depth of field. A “Shallow” depth of field refers to the phenomenon of having your subject in sharp focus but the objects in front of and/or behind your subject are out of focus. A “Long” depth of field refers to the phenomenon of having everything be in sharp focus from close to the camera to far away.
Diopter Correction - An adjustment on the viewfinder of a camera, allowing someone to adjust the viewfinder to their vision and removing the need to wear their glasses when looking through it. Diopter adjustments cannot compensate for all vision problems, only near and far sightedness can be compensated. Many digital cameras, particularly dslr’s, have a small dial next to the viewfinder where you can adjust the correction of the glass you are looking through to accommodate your own eyes (for nearsighted or farsightedness). If one photographer with 20/20 vision picks up a camera from another who is farsighted or nearsighted, he may look through the viewfinder and see everything blurry because the diopter has been adjusted by the farsighted/nearsited photographer to look sharp to them. However, so long as the camera is set to auto focus, the pictures taken should turn out sharp even if what they saw looked blurry through the viewfinder. Conversely, if that same photographer with 20/20 vision MANUALLY focused the lens to where he could see clearly through the viewfinder, the resultant capture would likely be out of focus. To correctly adjust the diopter the photographer should set the camera to auto focus on a hard line and let the camera auto focus to where it says the image is sharpest. Then the photographer adjusts the diopter on the viewfinder until the image looks sharp and in focus to them looking through the viewfinder. Now the diopter has been calibrated and even if they shoot in manual focus mode, so long as they dial it in to where it looks sharp to them, the image should be relatively sharp (assuming their eyesight hasn’t changed since it was last calibrated!)
Dodging – Selectively lightening part of a photo with an image editing program. The effect is often paired with “burning” (darkening) the dark areas as well. The process of using these editing tools to selectively darken shadows and brighten highlights is called “Dodge and Burn.”
DPI - (Dots Per Inch) - A measurement value used to describe either the resolution of a display screen or the output resolution of a printer. Obviously the higher the DPI, the better the resolution (to a certain extent). Depending on your output (a computer screen or printed photo), a higher DPI may increase the image quality (or may not). Many computer monitors have only a 72 DPI resolution so having an image with anything greater than 72 DPI will not look any better on your computer monitor than an image with only 72 DPI. A photo quality print however typically has about 300 DPI resolution. When you enlarge a photo digitally you effectively decrease the DPI thus reducing the quality of the image. So long as you can retain a 300 DPI resolution, you should have an outstanding print quality. Software programs like Photoshop Elements 6.0 can “interprolate” data in an image so if you enlarge it say beyond where you can get 300 DPI, you can tell Photoshop to add pixels to the image to keep it at 300 DPI. The software does this by adding pixels of similar color to the pixels around it in order to create more dots per inch. Technically this “upsampling” of an image degrades the image quality as the software is literally adding in pixels that never existed and will not perfectly represent what was captured. The more upsampling or interprolation is done, the more degredation the photo will have.
(more to come...)