In the context of images, a greyscale colour model represents a picture using only shades of grey, from pure black to pure white. There’s no colour information included. This is commonly used in black-and-white photography or to convert colour images into black and white.
- The greyscale colour model is used for:
- Converting colour images to black-and-white.
- Creating black-and-white images through cameras, scanners, and other input devices.
- Three algorithms are commonly used for greyscale conversion: the lightness method, the weighted average method, and the luminosity method.
- The greyscale colour model is not a simple linear scale from black to white but rather a method of converting colour brightness to reflect tonal relationships. When converting digital images to greyscale, each pixel is assigned a corresponding level of brightness based on its colour.
- When fully saturated spectral colours are converted to greyscale, their brightness typically ranges between 11% and 89%. For example:
- Red = 70%
- Orange = 40.38%
- Yellow = 11%
- Green = 41%
- Blue = 89%
- Violet = 74.06%
- Any RGB decimal colour value can be converted to greyscale. For instance, the RGB value for cyan converts to a greyscale value of 178, 178, 178. Similarly, HSB colour values can also be converted to greyscale, with the HSB value for pure yellow being Hue = 0, Saturation = 0, and Brightness = 11%.
The gravitational force, also called gravity, is one of the four fundamental forces in nature. The other forces are the electromagnetic force, the strong nuclear force and the weak nuclear force.
- Gravity is the phenomenon that attracts objects with mass or energy towards one another.
- It affects celestial bodies such as planets, stars, galaxies, and even light.
- The influence of gravity on smaller objects like human beings in the presence of larger ones, such as planets, is evident.
- Gravity, such as the Moon’s gravity, leads to ocean tides on Earth.
- Gravity accounts for the weight of physical objects. Its range is infinite, although its effects weaken as objects move farther apart
- Gravitational force is a universal force, meaning that it acts between all objects with mass, regardless of their composition or charge.
- Gravitational force is a long-range force, meaning that it can act between objects that are very far apart.
A raindrop is often represented as a geometrically perfect sphere, an idealized form that rarely exists in reality. This simplification helps in understanding the physics of rainbows, even though actual raindrops seldom maintain a perfectly spherical shape.
- Although the idealized geometry of raindrops aids in understanding rainbows, real raindrops vary in shape due to factors such as size, speed of descent, and turbulence. Each rainbow we observe is unique, shaped by chance and a range of environmental conditions.
- In summary, the form of a rainbow and the arrangement of raindrops within it depend on various changing factors, including the size, shape, and distribution of the droplets, the position of the sun, the observer’s location, atmospheric clarity and composition, and the presence of additional light sources or reflective surfaces. Every rainbow is a one-of-a-kind phenomenon, shaped by both random variations and the surrounding environment.
A retinal ganglion cell is a type of neuron located in the retina of the human eye. It receives visual information from photoreceptors through two types of intermediate neurons: bipolar cells and amacrine cells. Retinal ganglion cells transmit both image-forming and non-image-forming visual information to several regions in the brain, including the thalamus, hypothalamus, and midbrain.
- Retinal ganglion cells are located near the boundary between the retina and the central chamber containing the vitreous humour. They collect and process visual information from around forty different types of cells, including rods, cones, bipolar, horizontal, and amacrine cells. Once processed, this information is transmitted via their axons to higher visual centres in the brain
- The axons of ganglion cells form the fibres of the optic nerve, which synapse onto the lateral geniculate nucleus. Axons are long, slender projections of the cell body that typically conduct electrical impulses, known as action potentials, away from the neuron.
- In the fovea at the centre of the macula, a single ganglion cell communicates with as few as five photoreceptors, producing the highest possible resolution of detail. At the retina’s extreme periphery, however, a single ganglion cell receives input from thousands of photoreceptors.
- There are approximately twenty functional types of ganglion cells, which resolve visual information from 120 million rods and cones into a million parallel streams. These cells complete the foundation of visual processing in the retina, encoding the eye’s response to light and forming the fundamental building blocks of vision. Ganglion cells enable this encoding to converge into a unified representation of the visual world, creating the basis for human visual experience.
The term gamut or colour gamut is used to describe:
- The range of colours that a specific device or system can display or reproduce.
- The range of colours that the human eye can see in specific conditions.
- A range of colours that is smaller than all the colours that the human eye can see.
- All the colours in an image. Digitizing a photo, changing an image’s colour space, or printing an image onto paper might change its gamut.
- The range of perceived colours (visible to a human observer) is always greater than the range that can be reproduced by any digital device such as a screen, monitor or projector.
- Digital cameras, scanners, monitors, and printers all have limits to the range of colours they can capture, save, and reproduce.
- The main use of digital colour spaces and colour profiles is to set the gamut of colours that can be used to accurately reproduce or optimise the appearance of an image.
- It is currently impossible to make a digital device that can reproduce the same range of colours that the human eye can see.
Gamma correction, also referred to as gamma encoding, is an image processing technique that adjusts the brightness and contrast of an image to achieve a more natural and visually pleasing appearance.
- Gamma correction of digital images prevents excessive storage of information about highlights that are invisible to humans and ensures sufficient information is retained for shadows that require more differentiation to be observed.
- Gamma correction adjusts the relationship between the numerical value of a pixel stored in an image file (e.g., JPG or TIFF) and its corresponding brightness when displayed on-screen.
- Gamma correction is typically performed to compensate for the non-linear relationship between the input signal and the displayed brightness on a monitor or screen.
- In the case of a black-and-white image, a gamma function impacts highlights (brightest values), mid-tones (greyscale), and shadows (dark areas) in distinct ways.
- Gamma correction is not limited to black and white images but applies to colour images, where it affects colour balance and contrast.
Ganglion cells
Retinal ganglion cells are located near the boundary between the retina and the central chamber containing vitreous humour. They collect and process all the visual information gathered directly or indirectly from the forty-something types of rod, cone, bipolar, horizontal and amacrine cells and, once finished, transmit it via their axons towards higher visual centres within the brain.
The axons of ganglion cells form into the fibres of the optic nerve that synapse at the other end on the lateral geniculate nucleus. Axons take the form of long slender fibre-like projections of the cell body and typically conduct electrical impulses, often called action potentials, away from a neuron.
A single ganglion cell communicates with as few as five photoreceptors in the fovea at the centre of the macula. This produces images containing the maximum possible resolution of detail. At the extreme periphery of the retina, a single ganglion cell receives information from many thousands of photoreceptors.
Around twenty distinguishable functional types of ganglion cells resolve the information received from 120 million rods and cones into one million parallel streams of information about the world surveyed by a human observer in real-time throughout every day of their lives. They function to complete the construction of the foundations of visual experience by the retina, ordering the eyes response to light into the fundamental building blocks of vision. Ganglion cells do the groundwork that enables retinal encodings to ultimately converge into a unified representation of the visual world.
Ganglion cells not only deal with colour information streaming in from rod and cone cells but also with the deductions, inferences, anticipatory functions and modifications suggested by bipolar, amacrine and horizontal cells. Their challenge, therefore, is to enable all this data to converge and to assemble it into high fidelity, redundancy-free, compressed and coded form that can continue to be handled within the available bandwidth and so the data-carrying capacity of the optic nerve.
It is not hard to imagine the kind of challenges they must deal with:
- Information must feed into and support the distinct attributes of visual perception and be available to be resolved within the composition of our immediately present visual impressions whenever needed.
- Information must correspond with the outstanding discriminatory capacities that enable the visual system to operate a palette that can include millions of perceivable variations in colour.
- Information about the outside world must be able to be automatically cross-referenced, highly detailed, specifically relevant, spatial and temporally sequenced and available on demand.
- Information must be subjectively orientated in a way that it is locked at an impeccable level of accurate detail to even our most insane intentions as we leap from rock to rock across a swollen river or dive from an aircraft wearing only a wingsuit and negotiate the topography of a mountainous landscape speeding past at 260km per hour.
It is now known that efficient transmission of colour information is achieved by a transformation of the initial three trivariant colour mechanisms of rods and cones into one achromatic and two chromatic channels. But another processing stage has now been recognised that dynamically readjusts the eye’s trivariant responses to meet criteria of efficient colour information management and to provide us with all the necessary contextualising details as we survey the world around us. Discussion of opponent-processing is dealt with in the next article!