Sabatier Effect

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The Sabatier Effect refers to the phenomenon in which light areas appear dark and dark areas appear light on a negative. Additionally, a thin line appears in areas where the image has contrasting tones. When this effect occurs on a printed photo, it is known as solarisation.
While the Sabatier effect occurs when the film has been overexposed, solarisation takes place in the darkroom. However, contemporary terminology uses the terms interchangeably, rarely making the distinction between the sabatier effect and solarisation.
The Sabatier effect was accidentally developed during the 1800s when a photographic plate was inadvertently exposed to light before it had been processed, possible because the darkroom light had been turned on. Later, Man Ray popularized the Sabatier effect through his artwork.
Today, photographers can simulate the Sabatier effect by using an actinic light during the development process. However, while the Sabatier effect can produce dramatically intense photos, it is a difficult technique to master and consistently produce.

RGB

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The RGB system refers to a color model for film that is based on red, green and blue. From the basis of these three colors, the model constructs the rest of the colors in the image by mixing two or three of these colors in different proportions.
Although these colors are the basis of the colors in the image, none of these colors is specifically defined. Consequently, the red in one RGB color model may be significantly different than the red in a different system.
The CMYB color model, based on the cyan/magenta/yellow/black scale, is a common alternative to the RGB color system.
The original color model of an image is the platform from which the computer software like Photoshop can then effectively edit the image.
In addition to being central to photographic systems, color models such as RGB are also key to how LCD (liquid crystal display) screens and plasma television screens function.

Gamut

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A Gamut refers to the complete spectrum of colors that a given color system can produce. In photography, the gamut available will depend on whether the photographer is working with the RGB (red, green, blue) or the CMYK (cyan, magenta, yellow, key/black) color model.
Because each of these color systems starts with uniquely different set of primary colors, their combinations produce a distinct set of secondary and tertiary colors. For example, while the gamut of RGB includes a pure blue, that of CMYK will render a bluish purple. Depending of the subjects of the photograph and the desired effect, a photographer will elect one of the color models to have the resulting gamut in his photos.
If a color system lacks a certain shade within its gamut, then the color is “out of the gamut.”
Keep in mind that photographs don’t have to be in color to have a gamut. For example, pictures taken with black and white film or treated with sepia each have their own unique gamut. While black and white pictures will have a color spectrum that ranges from white to gray to black, the gamut for sepia toned pictures will span from white to light brown to dark brown.
Although it originated as a photographic term, gamut has come to have a broader meaning in the English language. In general terms, gamut can refer to any kind of spectrum.

Gamma

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A Gamma Correction, also known as gamma nonlinearity, gamma encoding or just gamma, refers to a nonlinear (logarithmic) equation that encodes or unravels the intensity of light in still photos or movies. Using gamma mapping, color systems, such as RGB or CMYK, can be made more uniform and smoother across a given plane or photographic surface.
Along with charting color uniformity and consistency, gamma can also catalog color contrast in a numeric form. While gamma correction may describe still photographs, it most often refers to images on computer movie screens.
Some common gamma values are the following:
+ PC images are encoded at 0.45 and decoded at 2.2
+ Mac images are encoded at 0.55 and decoded at 1.8.

Exposure

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Exposure is a term that relates the amount of light that is “exposed,” or shined upon, the film in a camera when a photograph is taken. When the film is properly exposed, the right amount of light has hit the film for the correct amount of time.
If film is overexposed, then too much light has hit the film for too long. Overexposure results in a photo that has minimal detail in the lighter areas and, therefore, appear to have large whiter spaces.
Conversely, underexposed negatives are produced when not enough light has been in contact with the film. Underexposed film will have more dark spaces that are poorly defined. Many camera manuals will state the camera’s exposure latitude, the range between underexposure and overexposure in which pictures will still turn out.
A photographer can manipulate the exposure for any given shot by opening or closing the camera’s aperture and by altering the shutter speed. Most cameras come with auto-exposure or exposure lock features. Auto-exposure tends to be most useful for amateurs. Experts recommend that you use the exposure lock mechanism in situations with highly contrasting light or with backlighting.
Exposure meters that measure a scene’s light are available to help a photographer calculate the appropriate exposure necessary for a given scene.

Color Wheel

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A Color wheel is a diagram that maps colors by their relationship to the other colors on the circle. While colors that are related to each other are placed side-by-side, complementary colors (colors that are inversely related to each other) are put on directly opposite sides of the color wheel.
In the color wheel, red, yellow and blue are considered primary colors while orange, green and purple are secondary colors.
The difference between primary and secondary colors on a color wheel lies in the fact that different blends of the three primary colors are responsible for creating each of the secondary colors.
When looking to find color balance in a photograph, it’s important to match complementary colors. The three different color systems are based on different combinations of primary colors.
RGB, the color space that most cameras use, is based on a Red/Green/Blue color wheel. The CYM color system is modeled with a Cyan/Magenta/Yellow color wheel. Finally, the RYB system relies on a Red/Yellow/Blue color wheel. The distinct color system a camera uses will produce an image within a defined color wheel. While painters rely on an RYB color wheel, photographers tend to capture their shots with either the RGB or CMY color wheel systems.

Color Temperature

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Color temperature, a term borrowed from physics, is the measurement (in Kelvins) of a color’s intensity on a scale of blue to red. In broad terms, color temperature refers to the visible light an object radiates based on its inherent heat.
While the red end of the color spectrum has a color temperature of 1,800K, colors that appear bluer fall within 16,000K. The following are the color temperatures of everyday sights: sunrise and sunset registers at around 1,600K; an electronic camera flash has a color temperature of 5,500K; a deep blue, cloudless sky emits 20,000K.
Ironically, warmer objects (those registering higher Kelvin temperatures) emit blue, a color that is traditionally considered to be a cooler color on the color wheel. Conversely, cooler objects radiate more reds, typically associated as a warmer color. For example, throughout a light bulb’s life, the bulb will appear red when it is hot. However, when the bulb is its hottest (i.e. just before it burns out), it will produce a visibly bluish light.
When the color of a photograph is off, the color sensitivity of the film hasn’t been properly calibrated to the color temperature of the photographed object. If you aren’t sure how to pair an object’s color temperature with the appropriately sensitive film, try using filters on your camera lens. Such filters can effectively balance a photo’s color.
Color temperature is also an important term in computer technology. Knowing your monitor’s range of color temperatures is key when you are choosing software for your system.