Subtractive Colour Theory Flashcards

Subtractive Colour Theory

• In additive colour theory, lights shining on a white surface combine to form different colours. This principle is fundamental in displays like computer screens and TVs, where red, green, and blue light combine to produce a wide range of colors.

  • Shining two primary colours creates a secondary colour.

  • Shining a secondary colour with its missing primary colour results in white.

  • Combining all three primary colours yields white. This is why white light can be separated into its constituent colors using a prism.

• If the surface is not white (e.g., yellow or green), different interactions occur. The reflected light will be altered based on the surface's color properties, leading to different color perceptions.

Interactions of Light with Surfaces

• Light interacts with physical matter through various means:

  • Absorption: Light energy is taken into the molecules of the surface.

  • Reflection (specular and diffuse): Light bounces off the surface. Specular reflection is from smooth surfaces (like mirrors), while diffuse reflection is from rough surfaces (like paper).

  • Transmission: Light passes through the surface, as seen in transparent materials.

  • Emission: Light is produced by the material itself (e.g., a light bulb or glowing paint).

• Reflection: Light bounces off the surface.

• Absorption: Light energy is taken into the molecules of the surface. The absorbed energy can be converted into heat or other forms of energy.

Subtractive Theory

• Light is not always fully reflected; it can be absorbed or partially reflected and absorbed. The specific wavelengths absorbed depend on the material's properties.

• When white light (Red, Blue, Green) interacts with a green plant:

  • Some colours are reflected, and some are absorbed.

  • The colours absorbed are SUBTRACTED from the original light.

  • The plant absorbs Red and Blue light while reflecting Green light. This is due to pigments like chlorophyll in the plant cells.

  • Only the green light is reflected to the eye, so the plant appears green.

• Reflection enables us to see objects. We see the light objects reflect. The intensity and color of the reflected light determine what we perceive.

• Clear objects (100% transmission) can be difficult to see due to lack of reflection. However, refraction and scattering can still make them visible.

Colour Combinations

• Different colours are made through reflection, starting from white light (Red+Blue+Green). The process involves selective absorption and reflection of different wavelengths.

  • Some light is absorbed, and some is reflected in each case. The balance between absorption and reflection determines the perceived color.

• Black:

  • Results when all colours of light are absorbed. Ideally, a black surface absorbs all incident light and reflects none.

  • (R+B+G) - R - B - G = 0 (nothing reflected)

• White:

  • Results when all colours of light are reflected. A white surface reflects all incident light equally.

  • (R+B+G) = R+B+G (all reflected)

Subtractive Primary Colours

• Important in mixing pigments in paint or ink, colour printing, and colour photography. These colors are essential for creating a wide range of hues by selectively absorbing certain wavelengths of light.

• Cyan, Magenta, and Yellow are the subtractive primary colours.

  • Each absorbs one of the additive primary colours.

  • White (R+B+G) - G = Magenta (R+B)

  • White (R+B+G) - R = Cyan (B+G)

  • White (R+B+G) - B = Yellow (R+G)

• Adding two subtractive primary colours filters/subtracts together will transmit/reflect one of the primary additive colours.

  • Magenta (R+B) - Yellow (R+G) = Red

  • Cyan (B+G) - Magenta (R+B) = Blue

  • Yellow (R+G) - Cyan (B+G) = Green

• Adding all three subtractive colour filters/subtracts together will absorb all the colours of the white light spectrum, resulting in black.

Human Sight

• Human sight combines additive and subtractive colour theories. The eye's ability to perceive color relies on both the addition of light from different sources and the subtraction of light by objects.

• Light reflected off objects stimulates eye cells (cones), and the brain interprets these signals as colour. Different types of cones are sensitive to different wavelengths of light: red, green, and blue.

• When multiple cone types (e.g., Red and Blue) are stimulated, their signals add together (e.g., to see Magenta). This additive process allows us to perceive a wide range of colors beyond just the primary colors.

Transmission

• Light can be subtracted through transmission (passing through a transparent object). The color of a transparent object is determined by the wavelengths of light it transmits.

• Transparent objects that subtract colours are called filters.

• Examples:

  • Magenta filter: Green is subtracted; Red and Blue are transmitted.

  • Yellow filter: Blue is subtracted; Red and Green are transmitted.

  • Cyan filter: Red is subtracted; Green and Blue are transmitted.

• Example with two filters:

  • Magenta filter subtracts green light and lets red and blue through. Then, yellow filter subtracts blue light from magenta, ultimately, no light would pass through.

Electromagnetic Spectrum

• Light consists of energy waves in the visible part of the electromagnetic spectrum. This spectrum includes a range of wavelengths from infrared to ultraviolet, but only a small portion is visible to the human eye.

• Our eyes interpret these energy waves as colours (Red, Orange, Yellow, Green, Blue, Indigo, Violet). Each color corresponds to a specific range of wavelengths within the visible spectrum.

• The visible spectrum is named as such because we can perceive