Communication Graphics Basic Vocabulary

Transcription

1 Communication Graphics Basic Vocabulary Aperture: The size of the lens opening through which light passes, commonly known as f-stop. The aperture controls the volume of light that is allowed to reach the lightsensitive material or digital sensor. Camera Obscura: Latin for dark chamber, a darkened room with a small opening through which rays of light may enter, projecting an image of the scene outside. Contrast: The difference in darkness or density between one tone and another. Daguerreotype: The first commercially successful photographic process, invented by Frecnhman Loius Daguerre and described by him in This process produced a positive image formed by mercury vapor on a metal plate coated with silver oxide. Density: The overall darkness of the image. Depth of Field: The area of an image that is acceptable sharp. In other words, what is in focus in a photograph. DoF is primarily controlled by the choice of aperture but is also affected by lens selection, subject to camera distance and digital sensor size.. Digital Noise: Is the presence of pixels whose color and brightness is unrelated to the subject. These random pixels most often appear in the dark areas of a digital image. While every digital image contains noise, those shot in lower lighting conditions or with longer exposures, tend to exhibit greater amounts of noise. Exposure: 1) The act of allowing to strike light-sensitive material (film or digital sensor.) 2) The amount of light reaching the light-sensitive material; specifically, the intensity of the light multiplied by the length of time it is allowed to strike the light-sensitive material. Flash: An Artificial light source, usually mounted directly on top of the camera. Use an electronic flash in very poor lighting. Set the camera to the suggested shutter speed for flash, and set the aperture based on the distance to the subject. Frame: The four edges of an image or an individual image. ISO: The relative sensitivity of a film or digital sensor. An ISO of 100 is less sensitive to light and requires more light to properly capture an image compared to and ISO of 400. The faster or more sensitive the ISO (the higher the ISO number) the more digital noise becomes noticeable.

2 Panning: 1) A motion effect where the subject seems almost frozen against a streaked or blurred background. Panning imparts a appearance of motion. Technique: Use slow shutter speeds (1/8, 1/15, 1/30) while following moving subjects with the camera during the exposure. Pixel: Short for picture element. Digital images are composed of many individual pixels, each having a specific color or tone that can be displayed, changed or stored. When the pixels are small enough, the eye merges the individual pixels into continuous tones. Shutter: A mechanism that opens and closes to admit light into a camera for a measure length of time. In other words, the shutter controls the duration of the exposure. Stop Action: A motion effect where the subject is sharp and seems to be frozen in time. Technique: Use a fast shutter speed, 1/250 th or faster, to freeze time on fast moving subjects. Since fast shutter speeds admit little light, be sure to shoot in bright light or use a high ISO. Underexposure: To give less than normal exposure to film or digital sensor. Opposite: Overexposure. Design & Compositional Elements Asymmetrical Balance: Objects, lines or shapes are NOT the same on both sides of an imaginary central line in an image. An example could be a photo of a building with a door in the middle, a window on one side and a bench on the other. Composition: The arrangement of items within an image. Leading Lines: Lines, either real or implied, that converge at a specific point in the photo, preferably at the subject or at the main point of interest. Radial Design: A radial design is one where objects seem to radiate from a central point outward to the edges of the frame in a circular pattern. An example might be a pinwheel or the iris of an eye. Repetition: Repeating shapes, lines, angles or patterns in an image. Look at the side of a building like Lamar High School. The placement of the windows is an example of repetition. Rule of Thirds: Deliberate placement of the subject, or main point of interest, at the junction of the lines of an imaginary tic-tac-toe grid. Symmetry: If you divide an image along a central line, both sides of the image would look the same. A building with a door in the middle and a window on each side would be an example of a symmetrical image.

3 Types of Light Axis Light: Comes from the direction of the camera, straight at the subject. Back Light: Comes toward the camera and lands on the opposite side of the subject from the camera. Contour Light: Side light that falls across the surface of the subject, giving it texture, volume and depth. Diffused Light: Soft, shadowless light, like what you might find on an overcast day. Edge Light: Back light that illuminates or highlights the edge of a subject. Also called Rim Light. Silhouette: This is also a form of backlight but in this case, no light touches the subject, rendering the subject solid black and two-dimensional. Exposure Concepts To get a correctly exposed image (an image that is neither too dark or too light) you need to expose the film or digital sensor to the correct amount of light. The camera typically has a built-in light meter that will help you achieve the correct balance of aperture, shutter speed and ISO for a particular scene. Aperture: Apertures, or f-stops, are lens opening measurements. Each successive opening is called a stop. When you open up the aperture by one stop, you double the amount of light that can reach the film or sensor. Similarly, when you close down the aperture, or stop down, the aperture by one stop you cut the amount of light by half. When considering aperture, think in terms of the volume of light that is allowed to enter the camera. A larger aperture, like f2, will allow more much more light to enter the camera than a smaller aperture, like f22. Typical lens opening sequence on a normal lens is: (Largest opening) (Smallest Opening) What is often confusing about the relationship between the aperture and its f-number is that the smaller opening has the larger number. For instance, f 22 is smaller than f 2.

4 The aperture, or f-stop, controls the depth of field, or amount of focus in a photograph. Maximum DoF is achieved with a small opening like f 22 and is sharp from foreground to background. Shallow DoF, on the other hand, has a very narrow area of focus within the image and is accomplished with a large aperture, like f 2. Shutter Speed: The shutter speed controls the amount of time that light is allowed to reach the film or sensor. The numbers on the shutter speed dial actually refer to a fraction of a second and represent the denominator of the fraction. 1/x (where x=shutter speed number.) For example, a shutter speed of 60 actually represents 1/60 th of a second. 1 represents 1/1 one one second. A shutter speed of 1000 represents 1/1000 th of a second. The bigger the number on the shutter speed dial, the less time the shutter is open. A 60 th of a second is a slower setting than 1000 th of a second. When considering shutter speed, think in terms of duration, the length of time, that light is allowed to strike the film or digital sensor. Each time you speed up your shutter speed by one stop, you cut the amount of time that the film or sensor see light in half. When you slow down your exposure by one stop, you double the amount of time that your film or sensor sees light. A typical shutter speed dial would have the following speed settings: B B stands for Bulb and is a manual setting that holds the shutter open as long as the shutter release button is held down. Shutter speed also controls the way motion is depicted in an image. A flying bird can appear frozen in mid-air with the selection of a fast shutter speed like 250 (which is the slowest speed to freeze motion.) Selecting a slower shutter speed, like 30 (actually 1/30 th of a second) can blur the motion of the bird s wings, giving it a sense of motion. Remember that you cannot hand-hold a camera (using a normal lens) without shaking at a shutter speed slower than 1/60 th of a second. Aperture and Shutter Speed together Once you determine what the proper light meter reading is for a particular scene, you may want to change one setting or another based on the effect that is caused by either aperture or shutter speed. If you change one setting you must change the other in the opposite direction to get a proper exposure. In other words, if you increase the volume of light that reaches your film or sensor by opening the aperture, you must decrease the duration of time that light enters the camera by cutting your shutter speed. More light requires less time and vise versa. If you open up the lens two stops, you must increase the shutter speed by two stops.

5 Exposure Problems Sometimes a suggested meter reading will not be the right combination of aperture and shutter speed for the type of effect you want for the image. Example: f 1/125 1/125 will not freeze 1/250 1/250 will freeze motion 1. Determine if the changed item (f-stop or ss) adds or cuts light or time 2. If it cuts time or light, add time or light to the other item. 3. Determine how many stops different the change is. 4. Adjust the other item by the same number of stops. 5. Remember, a change that adds more light needs a change of less time (and vice versa) in order for the image to be properly exposed. 6. Always change by the same number of stops. Digital Imaging Pixels: Are little squares of color that the computer or camera uses to record an image. The number of pixels per inch in an image determines its resolution. Resolution is measured in pixels per inch (ppi) or, more commonly, dots per inch (dpi.) More pixels per inch means the image will have more detail and be of better quality. 300 dpi is standard for print resolution. What that means is that a photograph with 300 dpi has enough information to give good definition in detailed areas and will, on good printers, very closely resemble a traditional photograph. However, 72 dpi is all that s needed to view an image on a computer monitor. Screen Resolution is considered very low, which is especially noticeable when you print an image from the web. Most websites store small images at low resolution to protect copyright. Images with high resolution are much larger files and take up more room on a computer. As a result, changes made to these images take longer to process. They will also take longer to print and to compress for display on the web or to send as an attachment. Once an image has been digitized, it is very difficult to increase its resolution so it s important to assign enough resolution for the kind of output you ultimately want. For instance, if you are scanning an image to be printed, be sure it has a resolution of at least 300 dpi and is scaled to the size you intend to print it. If you are using a digital camera and you plan to print the image at some point, be sure to capture the image at the highest quality your camera will allow. When you increase an image s resolution using software, the quality of the image does not improve. In fact, it will most likely look worse.

6 Very often when an image is saved, it will get compressed to maximize space. Several formats of compression are common. JPEG (displayed as.jpg at the end of a file name) is typically used to save images that will be printed, ed or displayed on the web. GIF (.gif) files also work for the web but are more frequently stored for website displays than for . TIFF (.tif) file can be opened by word-processing software. Most of these formats are able to be read regardless of which platform (Windows or Mac) created them.