Hue is one of the three main properties of colour, alongside saturation and brightness and is described using names such as red, yellow, green or blue.
- 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 arrange colours according to their hue.
- The most commonly used colour wheel is the RGB colour wheel, which includes primary colours (hues) 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.
The HSL colour model is similar to the HSB model. HSL refer to adjustments that can be made to hue, saturation and lightness to produce different colours. HSB refer to adjustments that can be made to hue, saturation and brightness to produce different colours.
- The HSL and HSB are very similar models and are often used interchangeably. They both represent colours based on Hue, Saturation, and a third component.
- In the HSB colour model brightness refers to the overall luminance of a colour.
- In the HSB colour model, brightness represents the colour independent of adding white or black. It’s like a dimmer switch for the chosen colour.
- In the HSL colour model, lightness refers to how light or dark a colour appears, considering how our eyes perceive brightness relative to a neutral grey. This is why a 50% light value represents a medium tone, even though it might not be the same brightness for all hues.
- Both the HSB colour model and the HSL colour model are usually represented as a cylinder, where the hue is represented by an angle around the central axis, the saturation is represented as the distance from the central axis, and the brightness or lightness is represented as a distance along the vertical axis.
- 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.
HSB colour values (codes) are numeric triplets used in software applications and programming to identify different colours.
- A numeric triplet is a code containing three parameters that refer to the hue, saturation, and brightness of a colour.
- For example:
- The HSB values for pure red are(0, 100%, 100%): Hue: 0°, Saturation: 100%, Brightness: 100%.
- A lighter, pastel version of red might be (0, 50%, 100%): Hue: 0°, Saturation: 50%, Brightness: 100%.
- A very dark, muted red could be: Hue (0, 100%, 20%): 0°, Saturation: 100%, Brightness: 20%.
- The values assigned to the three parameters can be used to define millions of different colours.
- Typically, 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.
The HSB colour model is similar to the RGB colour model insofar as it is an additive model based on RGB primary colours.
- 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 appears 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.
Horizontal cells are neurons that interconnect with other types of neurons within the retina of the human eye.
- 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.
Hexadecimal notation is a system for representing RGB colours. For example, a computer display would use the code #FF0000 to produce a bright red pixel. It is commonly used in digital applications such as web design and image processing, allowing for the accurate specification of up to 16,777,216 different colours.
- In hexadecimal notation, each of the three RGB colour components—red, green, and blue—is assigned a value between 00 and FF, where 00 represents no intensity and FF represents maximum intensity.
- For example:
- Red can have a value from 00 to FF (e.g., 00).
- Green is also assigned a value between 00 and FF (e.g., 0F).
- Blue follows the same pattern (e.g., FF).
- These three values form a six-digit hexadecimal triplet. For instance, the values above combine to form #000FFF, where the hash symbol (#) indicates hexadecimal notation.
- Some common colours and their hexadecimal representations are:
- Red (#FF0000)
- Yellow (#FFFF00)
- Green (#00FF00)
- Cyan (#00FFFF)
- Blue (#0000FF)
- Magenta (#FF00FF
Horizontal cells
Horizontal cells are connected to rod and cone cells by synapses and are classed as laterally interconnecting neurons.
Horizontal cells help to integrate and regulate information received from photoreceptor cells, cleaning up and globally adjusting signals passing through bipolar cells towards the regions 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.
If a scene contains objects that are much brighter than others, then horizontal cells are believed to prevent signals representing the brightest objects from dazzling the retina and degrading the overall quality of information.
Caption
The Neuronal Organization of the Retina Richard H. Masland
https://www.cell.com/neuron/fulltext/S0896-6273(12)00883-5?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0896627312008835%3Fshowall%3Dtrue
The hertz (symbol: Hz) is a unit used to measure the frequency of electromagnetic waves. It represents the number of wave-cycles per second.
- One hertz is defined as one cycle per second.
- Hertz measure the number of oscillations of the perpendicular electric and magnetic fields in electromagnetic radiation per second.
- Frequency conversions:
- 1 Hertz (Hz) = 1 cycle per second
- 1 Kilohertz (kHz) = 1,000 (thousand) cycles per second
- 1 Megahertz (MHz) = 1,000,000 (million) cycles per second
- 1 Gigahertz (GHz) = 1,000,000,000 (billion) cycles per second
- 1 Terahertz (THz) = 1,000,000,000,000 (trillion )cycles per second