or visual purple

Light-sensitive, purple-red organic pigment contained in the rod cells of the retina that allows the eye to see in black and white in dim light. It is composed of opsin, a protein, linked to retinal, a conjugated molecule (see conjugation) formed from vitamin A. Photons of light that enter the eye are absorbed by retinal and cause it to change its configuration, starting a biochemical chain of events that ends with impulses being sent along the optic nerve to the brain. In bright light, to protect rod cells from overstimulation, rhodopsin breaks down into retinal and opsin, both of which are colourless. In dim light or darkness the process is reversed (dark adaptation), and purple-red rhodopsin is reformed. Similar light-sensitive compounds made of retinal and other opsin proteins are the pigments in the retina's cone cells responsible for colour vision in bright light.

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The art and profession of selecting and arranging visual elements—such as typography, images, symbols, and colours—to convey a message to an audience. Sometimes graphic design is called “visual communications.” It is a collaborative discipline: writers produce words and photographers and illustrators create images that the designer incorporates into a complete visual message. Although graphic design has been practiced in various forms throughout history, it emerged as a specific profession during the job-specialization process that occurred in the late 19th century. Its evolution has been closely bound to developments in image making, typography, and reproduction processes. Prominent graphic designers include Jules Chéret, Piet Zwart, Paul Rand, Alexey Brodovitch, Milton Glaser, and David Carson.

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Perspective, in context of vision and visual perception, is the way in which objects appear to the eye based on their spatial attributes, or their dimensions and the position of the eye relative to the objects. There are two main meanings of the term: linear perspective and aerial perspective

Linear perspective

As objects become more distant, they appear smaller, because their angular diameter (visual angle) decreases. The visual angle of an object is the angle subtended at the eye by a triangle with the object at its base. The greater the distance of the object from the eye, the greater is the height of this triangle, and the less the visual angle. This follows simply from Euclidean geometry.

The Sun and the Moon appear to be roughly the same size because the Sun, although much, much larger, is also much farther away. The relationship between distance and apparent height of objects is not a linear pattern. If an object were actually touching the eye, thus being no distance away, it would appear infinitely tall.

Perspective is also seen in the way the parallel lines of how railway tracks appear to be meeting at a distant point (the vanishing point) on the horizon. When used in this sense, the 'horizon' is always at the level of the viewer's eye. Because the Earth is round, the true horizon (the line dividing the surface and the sky) is lower than this level. The difference is imperceptibly small when standing on the surface, but noticeable from great height (a person standing on a mountain can see further than someone at ground level). ''See horizon.

In graphic representation, an artist uses intuitive, artistic, scientific, or technical skills to represent the phenomenon of the visual perception of perspective. In simpler terms, these skills are used to add a suggestion of depth to what is ultimately a flat image or drawing. See Perspective (graphical).

Forced perspective can be used to deliberately misrepresent an object's size, making something appear larger or smaller than it really is. This is common in film, where a distant castle in the background may in fact only be a cardboard model a few feet high (and much closer to the camera). These are forms of optical illusions.

Aerial perspective

Aerial perspective refers to the effect on the appearance of an ordinary object (i.e., other than a self-luminous object by being viewed through the atmosphere. In daylight, as an ordinary object gets further from the eye, its contrast with the background is reduced, its colour saturation is reduced, and its colour becomes more blue.

Film, television, and computer/video gaming

Perspective in film, television, and computer and video games can include first-person view, third-person view, and other camera field of view effects.

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