digital photography principles of light and color

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  • Digital PhotographyPrinciples of Light and Color

  • ISOThe ISO speed is a numeric indication of the cameras sensitivity to light.A higher ISO number indicates a higher sensitivity to light. This is better for low light and moving subjects. However, the image may look more grainy with noise.A low ISO speed is better for brightly lit subjects and subjects that are stationary. The image quality is finer with less noise.

  • Color provides the photographer with an additional dimension of control in organizing pictorial elements.

    Emphasis and subordination of selected details can be achieved not only through control of Depth of Field, leading lines, the Rule of Thirds, Size, and Focus, but also by the arrangement of color details within the photograph.

  • Color HarmonyColor HarmonyThe relationship among various color details in the photo.

    Color details may be emphasized or subordinated by setting them next to objects or against backgrounds of contrasting colors.

    Color elements should be organized to avoid distracting color details in the background and along the edges.

  • Hue, Value, SaturationHuecolor, or the classification of a color. Here the center bar seems to shift in Hue.

    Valuerelative lightness or darkness of a color. Here the center bar seems to shift in Value.

    Saturationconcentration of the color, degree of the color. Here the center bar seems to shift in Saturation.

  • The Color WheelPrimary Light ColorsRed, Blue, and Green. The combination of these three pure hues produces White Light.

    Secondary Light ColorsCyan, Magenta, and Yellow. Each secondary color is a combination of two primary colors. Each color appears exactly opposite its own complement.

  • Color HarmonyWhen any color appears against a complementary background color of lower saturation and value, its own hue is enhanced.

    When any color appears against a background of equal saturation and value, however, complementary colors compete for attention, often appearing to clash and vibrate disharmony.

  • Color HarmonyEven objects of the same hue may contrast if one is more highly saturated than the other.

    Appropriate contrast can be developed even in monochromatic compositionsthose based on one hue or several closely related huesby controlling their saturations and values.

  • Additive Color TheoryThe human eye is sensitive to the three primary light colors: red, green, and blue.

    These colors have been created from a blend of the spectrum in equal 1/3 amounts. Mixing the three colors in equal amounts creates white light.

    This is the basis of the statement: White is the presence of all color.

  • Additive Color TheoryCombining two of the primary colors equally creates a secondary color.

    Red + Green = YellowGreen + Blue = CyanBlue + Red = MagentaRed + Blue + Green = White

    The term Additive describes colors that add color instead of taking anything away.Color television is based upon additive color theory.

  • Subtractive Color TheoryThe three main subtractive colors are yellow, cyan, and magenta.

    They are also secondary colors.

    Combining all three of the subtractive colors in equal amounts gives a near black.

    This is the basis for the statement: Black is the absence of all color.

  • Subtractive Color TheoryCombining two subtractive colors equally recreates one of the primary colors.

    Yellow + Magenta = RedMagenta + Cyan = BlueCyan + Yellow = GreenCyan + Magenta + Yellow = Black

    Subtractive colors do actually subtract (filter out) some color, but they do allow the majority of color to pass through.Color film is based upon subtractive color theory.

  • The Effects of Reflected LightAs long as the light reaching the photo sensor is matched to the color temperature for which the photo sensor is balanced, the image will match the hues of the original scene.

    When the light source and photo sensor are not matched, the image will have a cast showing the mismatch.

    Light rays reflected from an object assume the hues of the object and lend them to other objects upon which they fall.

    Light reflected from the green leaves of a tree will provide a greenish cast to a white T-shirt on a subject standing under the tree.

    Our brain corrects this for our eyes, but the camera is more faithful. Any object of strong color will influence the cast of other objects.

    To avoid this separate strongly colored objects from other objects.

  • Color TemperatureSunlight is the best light to view all colors found in the visible spectrum. It serves as the standard by which all artificial light is measured.

    Color Temperature is one way to describe the quality of a light source.

    It is measured based on the Kelvin Scale.

  • Color Temperature

    1500oK Candlelight 2680oK 40W Incandescent Lamp 3000oK 200W Incandescent Lamp3400oK Tungsten lamp5500-5600oK Electronic Flash6500oK Average Daylight8000oK Overcast sky11000-13000oK Blue Sky w/out direct sunlight

  • Color TemperatureEarly morning and evening sunlight tend to contain high levels of yellow. A regular light bulb also will have more yellow hue.

    Overcast sky tends to be bluish in color.

    Fluorescent lighting tends to have a green hue to it when using daylight balanced film.

  • White BalanceThe three RGB (red, green, blue) primary colors exist in the light source in varying proportions depending on the color temperature. When the color temperature is high there is more blue. When it is low there is more red.To the human eye a white object looks white regardless of the type of lighting. With a digital camera the color temperature can be adjusted to make the image look more natural. The subjects white color is used as the criteria for adjusting the other colors.

  • Psychological effects of colorColors have a lot of interpretations associated to context.

    Red the traditional color of hate and anger, may suggest the feeling of love and contentment in a cozy fire lit scene.

    Blue usually the color of cold, ice, and darkness, if taken of a clear blue sky over a sandy beach may give a sense of warmth and summertime.

  • Psychological effects of colorSome guidelines:The red-orange-yellow hues tend to appear brighter to the eye. These are often called the warm tones. They tend to convey a greater sense of activity.

    The greater the color contrasts within a photo, the more active and dynamic the feeling the photo will tend to convey.

    Monochromatic compositionsthose developed around a few closely related hues will convey a sense of restfulness and stillness.

  • Capturing ColorEach photosite in the camera is colorblind. It only keeps track of the total intensity of the light that strikes its surface. In order to get a full color image, most sensors use filtering to look at the light in its three primary colors. Once the camera records all three colors, it combines them to create the full spectrum.

  • Capturing ColorThere are several ways of recording the three colors in a digital camera. The highest quality cameras use three separate sensors, each with a different filter. A beam splitter directs light to the different sensors. Each sensor gets an identical look at the image; but because of the filters, each sensor only responds to one of the primary colors.

  • Capturing ColorAnother method is to rotate a series of red, blue and green filters in front of a single sensor. The sensor records three separate images in rapid succession. This method also provides information on all three colors at each pixel location; but since the three images aren't taken at precisely the same moment, both the camera and the target of the photo must remain stationary for all three readings. This isn't practical for candid photography or handheld cameras.

  • Capturing ColorA more economical and practical way to record the primary colors is to permanently place a filter called a color filter array over each individual photosite. By breaking up the sensor into a variety of red, blue and green pixels, it is possible to get enough information in the general vicinity of each sensor to make very accurate guesses about the true color at that location. Interpolation: A technique used by digital cameras, scanners and printers to increase the size of an image in pixels by averaging the color and brightness values of surrounding pixels The most common pattern of filters is the Bayer filter pattern. This pattern alternates a row of red and green filters with a row of blue and green filters. The pixels are not evenly divided -- there are as many green pixels as there are blue and red combined. it's necessary to include more information from the green pixels in order to create an image that the eye will perceive as a "true color."

  • Capturing ColorThe advantages of this method are that only one sensor is required, and all the color information (red, green and blue) is recorded at the same moment. That means the camera can be smaller, cheaper, and useful in a wider variety of situations. The raw output from a sensor with a Bayer filter is a mosaic of red, green and blue pixels of different intensity.

    Digital cameras use specialized demosaicing algorithms to convert this mosaic into an equally sized mosaic of true colors. The true color of a single pixel can be determined by averaging the values from the closest surrounding pixels.

    Most consumer cameras on the market today use a single sensor with alternating rows of green/red and green/blue filters.

  • Think, Pair ShareA:Hue, Value, SaturationName the Primary ColorsName the Secondary Colors Define a Monochromatic composition

    B:Cast Color Tempe