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In photography and cinematography, a multiple exposure is the superimposition of two or more exposures to create a single image, and double exposure has a corresponding meaning in respect of two images. The exposure values may or may not be identical to each other.
Ordinarily, cameras have a sensitivity to light that is a function of time. For example, a one-second exposure is an exposure in which the camera image is equally responsive to light over the exposure time of one second. The criterion for determining that something is a double exposure is that the sensitivity goes up and then back down. The simplest example of a multiple exposure is a double exposure without flash, i.e. two partial exposures are made and then combined into one complete exposure. Some single exposures, such as "flash and blur" use a combination of electronic flash and ambient exposure. This effect can be approximated by a Dirac delta measure (flash) and a constant finite rectangular window, in combination. For example, a sensitivity window comprising a Dirac comb combined with a rectangular pulse, is considered a multiple exposure, even though the sensitivity never goes to zero during the exposure.
In the historical technique of chronophotography, dating back to the Victorian era, a series of instantaneous photographs were taken at short and equal intervals of time. [1] These photographs could be overlayed for a single multiple exposure print.
In photography and cinematography, multiple exposure is a technique in which the camera shutter is opened more than once to expose the film multiple times, usually to different images. The resulting image contains the subsequent image/s superimposed over the original. The technique is sometimes used as an artistic visual effect and can be used to create ghostly images or to add people and objects to a scene that were not originally there. It is frequently used in photographic hoaxes.
It is considered easiest to have a manual winding camera for double exposures. On automatic winding cameras, as soon as a picture is taken the film is typically wound to the next frame. Some more advanced automatic winding cameras have the option for multiple exposures but it must be set before making each exposure. Manual winding cameras with a multiple exposure feature can be set to double-expose after making the first exposure.
Since shooting multiple exposures will expose the same frame multiple times, negative exposure compensation must first be set to avoid overexposure. For example, to expose the frame twice with correct exposure, a −1 EV compensation have to be done, and −2 EV for exposing four times. This may not be necessary when photographing a lit subject in two (or more) different positions against a perfectly dark background, as the background area will be essentially unexposed.
Medium to low light is ideal for double exposures. A tripod may not be necessary if combining different scenes in one shot. In some conditions, for example, recording the whole progress of a lunar eclipse in multiple exposures, a stable tripod is essential.
More than two exposures can be combined, with care not to overexpose the film.
Digital technology enables images to be superimposed over each other by using a software photo editor, such as Adobe Photoshop or the GIMP. These enable the opacity of the images to be altered and for an image to be overlaid over another. They also can set the layers to multiply mode, which 'adds' the colors together rather than making the colors of either image pale and translucent.
Many digital SLR cameras allow multiple exposures to be made on the same image within the camera without the need for any external software. And some bridge cameras can take successive multiple exposures (sometimes up to nine) in one frame and in one shot. It is the same with high-dynamic-range imaging, which takes multiple shots in one burst captures, then combines all the proper shots into one frame. [2]
In addition to direct photographic usage of the technique, fine artists' work has been inspired by the multiple exposure effect. Examples include Joan Semmel's oil on canvas "Transitions" from 2012, [3] [4] and Ian Hornak's acrylic on canvas "Hanna Tillich's Mirror: Rembrandt's Three Trees Transformed Into The Expulsion From Eden", from 1978 (depicted).
With traditional film cameras, a long exposure is a single exposure, whereas with electronic cameras a long exposure can be obtained by integrating together many exposures. This averaging also permits there to be a time-windowing function, such as a Gaussian, that weights time periods near the center of the exposure time more strongly. Another possibility for synthesizing long exposure from a multiple exposure is to use an exponential decay in which the current frame has the strongest weight, and previous frames are faded out with a sliding exponential window.
Multiple exposure technique can also be used when scanning transparencies like slides, film or negatives using a film scanner for increasing dynamic range. With multiple exposure the original gets scanned several times with different exposure intensities. An overexposed scan lights the shadow areas of the image and enables the scanner to capture more image information here. Afterwards the data can be calculated into a single HDR image with increased dynamic range.
Among the scanning software solutions which implement multiple exposure are VueScan and SilverFast.
Chroma key compositing, or chroma keying, is a visual-effects and post-production technique for compositing (layering) two or more images or video streams together based on colour hues. The technique has been used in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture, and video game industries. A colour range in the foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as colour keying, colour-separation overlay, or by various terms for specific colour-related variants such as green screen or blue screen; chroma keying can be done with backgrounds of any colour that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from any human skin colour. No part of the subject being filmed or photographed may duplicate the colour used as the backing, or the part may be erroneously identified as part of the backing.
A camera is an optical instrument used to capture and store images or videos, either digitally via an electronic image sensor, or chemically via a light-sensitive material such as photographic film. As a pivotal technology in the fields of photography and videography, cameras have played a significant role in the progression of visual arts, media, entertainment, surveillance, and scientific research. The invention of the camera dates back to the 19th century and has since evolved with advancements in technology, leading to a vast array of types and models in the 21st century.
A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devices like smartphones with the same or more capabilities and features of dedicated cameras. High-end, high-definition dedicated cameras are still commonly used by professionals and those who desire to take higher-quality photographs.
Special effects are illusions or visual tricks used in the theatre, film, television, video game, amusement park and simulator industries to simulate the imagined events in a story or virtual world.
In photography, shutter speed or exposure time is the length of time that the film or digital sensor inside the camera is exposed to light when taking a photograph. The amount of light that reaches the film or image sensor is proportional to the exposure time. 1⁄500 of a second will let half as much light in as 1⁄250.
In photography, exposure is the amount of light per unit area reaching a frame of photographic film or the surface of an electronic image sensor, as determined by shutter speed, lens F-number, and scene luminance. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.
Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system introduced in the mid-1970s. A closely related ISO system is used to describe the relationship between exposure and output image lightness in digital cameras. Prior to ISO gaining traction the best known systems were ASA in the U.S. and DIN in Europe.
In photography and videography, multi-exposure HDR capture is a technique that creates extended or high dynamic range (HDR) images by taking and combining multiple exposures of the same subject matter at different exposure levels. Combining multiple images in this way results in an image with a greater dynamic range than what would be possible by taking one single image. The technique can also be used to capture video by taking and combining multiple exposures for each frame of the video. The term "HDR" is used frequently to refer to the process of creating HDR images from multiple exposures. Many smartphones have an automated HDR feature that relies on computational imaging techniques to capture and combine multiple exposures.
In photography, bracketing is the general technique of taking several shots of the same subject using different camera settings, typically with the aim of combining the images in postprocessing. Bracketing is useful and often recommended in situations that make it difficult to obtain a satisfactory image with a single shot, especially when a small variation in exposure parameters has a comparatively large effect on the resulting image. Given the time it takes to accomplish multiple shots, it is typically, but not always, used for static subjects. Autobracketing is a feature of many modern cameras. When set, it will automatically take several bracketed shots, rather than the photographer altering the settings by hand between each shot.
Film look is a process in which video is altered in overall appearance to appear to have been shot on film stock. The process is usually electronic, although filmizing can sometimes occur as an unintentional by-product of some optical techniques, such as telerecording. The effect is the exact opposite of a process called VidFIRE.
Compositing is the process or technique of combining visual elements from separate sources into single images, often to create the illusion that all those elements are parts of the same scene. Live-action shooting for compositing is variously called "chroma key", "blue screen", "green screen" and other names. Today, most, though not all, compositing is achieved through digital image manipulation. Pre-digital compositing techniques, however, go back as far as the trick films of Georges Méliès in the late 19th century, and some are still in use.
Time-lapse photography is a technique in which the frequency at which film frames are captured is much lower than the frequency used to view the sequence. When played at normal speed, time appears to be moving faster and thus lapsing. For example, an image of a scene may be captured at 1 frame per second but then played back at 30 frames per second; the result is an apparent 30 times speed increase. Similarly, film can also be played at a much lower rate than at which it was captured, which slows down an otherwise fast action, as in slow motion or high-speed photography.
In photography, a shutter is a device that allows light to pass for a determined period, exposing photographic film or a photosensitive digital sensor to light in order to capture a permanent image of a scene. A shutter can also be used to allow pulses of light to pass outwards, as seen in a movie projector or a signal lamp. A shutter of variable speed is used to control exposure time of the film. The shutter is constructed so that it automatically closes after a certain required time interval. The speed of the shutter is controlled either automatically by the camera based on the overall settings of the camera, manually through digital settings, or manually by a ring outside the camera on which various timings are marked.
Mattes are used in photography and special effects filmmaking to combine two or more image elements into a single, final image. Usually, mattes are used to combine a foreground image with a background image. In this case, the matte is the background painting. In film and stage, mattes can be physically huge sections of painted canvas, portraying large scenic expanses of landscapes.
In photography, through-the-lens metering refers to a feature of cameras whereby the intensity of light reflected from the scene is measured through the lens; as opposed to using a separate metering window or external hand-held light meter. In some cameras various TTL metering modes can be selected. This information can then be used to set the optimal film or image sensor exposure, it can also be used to control the amount of light emitted by a flash unit connected to the camera.
Night photography refers to the activity of capturing images outdoors at night, between dusk and dawn. Night photographers generally have a choice between using artificial lighting and using a long exposure, exposing the shot for seconds, minutes, or even hours in order to give photosensitive film or an image sensor enough time to capture a desirable image. With the progress of high-speed films, higher-sensitivity digital sensors, wide-aperture lenses, and the ever-greater power of urban lights, night photography is increasingly possible using available light.
Redscale is a technique of shooting photographic film where the film is exposed from the wrong side, i.e. the emulsion is exposed through the base of the film. Normally, this is done by winding the film upside-down into an empty film canister. The name "redscale" comes because there is a strong color shift to red due to the red-sensitive layer of the film being exposed first, rather than last [the red layer is normally the bottom layer in C-41 film]. All layers are sensitive to blue light, so normally the blue layer is on top, followed by a filter. In this technique, blue light exposes the layers containing cyan and magenta dyes, but the layer containing yellow dye is left unexposed due to the filter. E-6 film has also been used for this technique.
Rolling shutter is a method of image capture in which a still picture or each frame of a video is captured not by taking a snapshot of the entire scene at a single instant in time but rather by scanning across the scene rapidly, vertically, horizontally or rotationally. In other words, not all parts of the image of the scene are recorded at exactly the same instant. This produces predictable distortions of fast-moving objects or rapid flashes of light. This is in contrast with "global shutter" in which the entire frame is captured at the same instant.
Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and resolution of the film.
Google Camera is a camera phone application developed by Google for the Android operating system. Development for the application began in 2011 at the Google X research incubator led by Marc Levoy, which was developing image fusion technology for Google Glass. It was publicly released for Android 4.4+ on the Google Play Store on April 16, 2014. It was initially supported on all devices running Android 4.4 KitKat and higher, but became only officially supported on Google Pixel devices in the following years.
