Dictionary tag: H

• One hertz is defined as one complete cycle of oscillation per second.
• Hertz measure the number of complete oscillations of the perpendicular electric and magnetic fields of electromagnetic radiation per second.
• 1 Hertz (Hz) = 1 complete cycle of oscillation per second.
• 1 Kilohertz (kHz) = 1,000 (thousand) complete cycles of oscillation per second.
• 1 Megahertz (MHz) = 1,000,000 (million) complete cycles of oscillation per second.
• 1 Gigahertz (GHz) = 1,000,000,000 (billion) complete cycles of oscillation per second.
• 1 Terahertz (THz) = 1,000,000,000,000 (trillion) complete cycles of oscillation per second.

• Hexadecimal notation has a base (radix) of 16, whereas decimal notation uses a base of 10.
• Hexadecimal notation is often used in computing and digital systems because it is a convenient way to represent large numbers in a compact and easy-to-read format.
• The decimal system of notation uses nine digits, 0 to 9, and adds columns to the right to denote units of 10s, 100s, etc.
• A hexadecimal system of notation uses sixteen digits. The digits 0-9 represent values from zero to nine, and A-F (or a-f) represent values from ten to fifteen. Further columns are added to represent units of 16, 256, etc.
  • The rightmost digit represents units (16^0)
  • The second-rightmost digit represents 16s (16^1)
  • The third-rightmost digit represents 256s (16^2), and so on.
• A hexadecimal triplet is a six-digit, three-byte hexadecimal system of notation used in programming and software applications (such as graphic design, web development, and photography) to represent colours. The bytes represent the red, green, and blue components of a colour, in that order.
• Each byte represents a number in the range 00 to FF in hexadecimal notation, which is equivalent to 0 to 255 in decimal notation.
• The hash symbol (#) is used to indicate hexadecimal notation.
• Specific colours can be represented in hexadecimal notation, such as red (#FF0000), yellow (#FFFF00), green (#00FF00), cyan (#00FFFF), blue (#0000FF), and magenta (#FF00FF).

• Horizontal cells are one of several types of neurons found in the retina of the human eye. The other types include photoreceptor cells (rods and cones), bipolar cells, amacrine cells, and ganglion cells.
• Horizontal cells interconnect with rod and cone cells via synapses, which is why they are often referred to as laterally interconnecting neurons.
• Horizontal cells help to integrate and regulate photoreceptor cells, cleaning up and globally adjusting signals passing through bipolar cells toward the region containing ganglion cells.
• An important function of horizontal cells is enabling the eye to adjust to both bright and dim light conditions. They achieve this by providing feedback to rod and cone photoreceptors about the average level of illumination falling onto specific regions of the retina.
• Horizontal cells are believed to prevent signals representing the brightest objects in a scene from dazzling the retina and degrading the quality of information.

Both RGB and HSB are additive colour models with red, green and blue primary colours. But whilst RGB relies on directly adjusting the amount of red, green and blue light needed to produce other colours the HSB colour model relies on adjusting hue, saturation and brightness.

• Hue refers to the perceived difference between colours and is usually described using names such as red, yellow, green, or blue.
  • Hue can be measured as a location on an HSB colour wheel and expressed as a degree between 0 and 360.
• Saturation refers to the vividness of a colour compared to an unsaturated colour.
  • Saturation is measured between a fully saturated colour (100%) and an unsaturated colour (0%)that appear either:
    • Dull and washed out until all colour disappears, leaving only a monochromatic grey tone (0%).
    • Misty or milky the nearer they are to white.
  • On many HSB colour wheels, saturation decreases from the edge to the centre.
• Brightness refers to the perceived difference in the appearance of colours under ideal sunlit conditions compared to poor lighting conditions where a hue’s vitality is lost.
  • Brightness can be measured as a percentage from 100% to 0%.
  • As the brightness of a fully saturated hue decreases, it appears progressively darker and achromatic.

HSB colour model in practice

In the implementation of the HSB colour model used in Adobe Illustrator CC:

• The HSB colour model can be accessed in the Colour Panel.
• If the Colour Panel is not visible, find it in the Windows menu.
• To switch from the default RGB setting to HSB, click on the hamburger menu (icon with three horizontal lines) in the top right of the panel.
• Hue, saturation, and brightness can all be adjusted using the sliders or by clicking anywhere on the HSB Spectrum.
• To enter an HSB colour using hexadecimal notation, switch back to the RGB colour model using the hamburger menu and enter the code in the provided window.
• HSB notation typically appears as follows:
  • H = 0^0, S = 100%, B = 100% produce a fully saturated primary red hue with maximum brightness.
  • H = 0⁰, S = 100%, B = 50% produce a fully saturated primary red hue that has lost some of its brightness so appears much darker in colour.
  • H = 0⁰, S = 50%, B =  100% produce a bright but less saturated primary red hue.

• A numeric triplet is a code containing three parameters that refer to the hue, saturation, and brightness of a colour.
• The values assigned to each of these three parameters can be used to define millions of different colours.
• In Adobe Illustrator CC, the HSB colour model is implemented as follows:
  • Hue is represented in degrees from 0 to 360, corresponding to locations on the circumference of a colour wheel.
  • Saturation is represented as a percentage, where 100% denotes a fully saturated colour, and 0% denotes a fully desaturated colour.
  • Brightness is represented as a percentage, where 100% denotes the highest luminance of a colour, and 0% denotes the darkest possible shade of a colour.

• In the HSB colour model, brightness refers to the perceived intensity of light insofar as it affects the appearance of a colour.
  • Brightness (which in some situations is referred to as value) represents the intensity of a colour. Brightness ranges from 0% (completely black) to 100% (full brightness, of the colour).
  • In the HSB model, the brightness component represents the actual brightness of the colour in a more straightforward manner, without considering the perceptual aspects.
  • The HSB colour space is usually represented as a cylinder, where the hue is represented by an angle around the central axis, the saturation is represented as distance from the central axis, and the brightness is represented as distance along the vertical axis.

HSV_color_solid_cylinder.png: SharkDderivative work: SharkD  Talk, CC BY-SA 3.0, via Wikimedia Commons

• In the HSL colour model, lightness refers to the perceived intensity of light insofar as it affects the appearance of a colour.
  • Lightness, represents the perceived brightness of a colour relative to a neutral grey. Lightness ranges from 0% (completely black) to 100% (completely white), with 50% representing the mid-tone and fully saturated colour.
  • In the HSL model, the lightness component aims to perceptually represent the brightness of the colour, taking into account how our eyes perceive brightness in different hues. As a result, it can be more visually consistent.
  • The HSL colour space is usually represented as a cylinder, where the hue is represented by an angle around the central axis, the saturation is represented as distance from the central axis, and the lightness is represented as distance along the vertical axis.

HSL_color_solid_cylinder.png: SharkDderivative work: SharkD  Talk, CC BY-SA 3.0, via Wikimedia Commons

• The difference between the two models lies in how the lightness and brightness components are calculated. In HSB, the brightness value is calculated by summing the highest and lowest RGB components and then dividing by two. In HSL, the lightness value is calculated by averaging the highest and lowest RGB components.
• Both models are used to represent colours in a way that is more intuitive and user-friendly for adjustments compared to the RGB model.
• Due to the similarity between HSB and HSL, they are often used interchangeably, and the difference in implementation is minor. Many software applications, including Adobe software, implement HSB (Hue, Saturation, Brightness) as a way to adjust colours easily and intuitively.

• Hue refers to the colour of an object or light source, and is determined by the dominant wavelength of light it emits or reflects.
• Hue is often used to describe colours in terms of their position on the colour wheel/ Colour wheels are circular diagrams that arranges colours according to their hue.
• The most commonly used colour wheel is the RGB colour wheel, which includes primary colours of red, green and blue, as well as secondary and tertiary colours.
• Hues can be warm or cool, depending on their position on the colour wheel. Warm hues are those that include red, orange and yellow, while cool hues include blue, green and purple.
• The perceived brightness and saturation of a hue can be affected by its surrounding colours, as well as by lighting conditions.
• The perception of hue is also influenced by cultural and personal associations, as well as context and other environmental factors.
• In the fields of art, design and visual communication, a good understanding of hue is essential for creating effective and visually appealing colour schemes.
• In digital imaging and colour reproduction, hue can be adjusted through techniques such as colour correction and colour grading, to achieve the desired colour balance and tone.

About the term hue here at lightcolourvision.org

• At lightcolourvision.org, we use the term “hue” to refer to the attribute of a colour that distinguishes it from other colours on the colour spectrum.
• Colour models analyse and describe colours and their attributes in various ways. Some are grounded in the way the human eye perceives colours, others provide mathematical explanations.
• The RGB colour model is a widely used additive colour model that describes colours in terms of the amounts of red, green, and blue light that are combined to create the colour.
• In the HSB colour model, hue is one of the three attributes that describe a colour, alongside saturation and brightness.
• The HSB colour model is commonly used in digital design and is a popular way to describe colours on electronic devices like televisions, computers, and mobile phones.
• The CMYK colour model is used in print and focuses on the colours created by mixing cyan, magenta, yellow, and black inks on paper. Because the CMYK model doesn’t explicitly use the term “hue,” it is not a primary concern when designing for print.