Lecture 2 - light, the eye, and perception
Light
Light helps us to see objects, The sun, a lit candle and electric bulbs all give out light, there known as luminous bodies.
light shines from them and reflects off of other objects, they then beam into our eyes and get decoded by our brain for us to see an image.
In the 17th century, two scientists had different views on the nature of light.
Newton - Light consists of Particles
Huygens - Light is made of Waves
In Late 1600s, Sir Isaac Newton believed that light travels in the form of particles which he named as “corpuscles”.
1678 Christian Huygens argued that light might be some sort of a wave motion.
Huygens came up with Huygens's Principle. He deduced the Laws of Reflection and Refraction to prove the theory of light is a Wave, But he could not explain why light has different colours.
In 1900, Max Planck was able to explain light energy is quantized. That quantum of light energy was later named a PHOTON.
Colour
Huygens deduced the Laws of Reflection and Refraction to prove the theory of light is a Wave.
Isaac Newton discovered that white light consists of seven* colours.
He found that if a beam of white light is passed through a glass prism then it will split in to seven* colours.
*we always refer to it as 7 although it is more
ROYGBIV
Worlds first person to invent a pink Floyd album cover 😂😂😂
Spectrum of visible light: The band of colours is formed when a beam of white light is passed through a glass prism is called the spectrum of white light or visible spectrum.
Dispersion of light: The splitting of white light into colours on passing through a transparent medium is called dispersion of light.
The light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted.
As a result, red light is refracted the least and violet light is refracted the most - causing the coloured light to spread out to form a spectrum.
This is called dispersion.
Luminous bodies tend to emit different types of radiation from the EMS (electromagnetic spectrum) the sun gives us visible light, ultra violet, infrared, as well as others.
Limited in Colour Range and Intensity Range
Three Types of eyes
non-compound eyes (mammals) - Refractive cornea - like a camera
Compound eyes (insects)
Ocelli - eye spots - basic eyes
Compound
The compound eyes of insects, are composed of units called ommatidia.
An ommatidium contains a cluster of photoreceptor cells surrounded by support cells and pigment cells.
The outer part of the ommatidium is overlaid with a transparent cornea.
Ocelli
Ocelli (singular Ocellus) are simple photo-receptors.
No additional structures such as a cornea and lens.
Unlike compound eyes, ocelli do not form a complex image of the environment but are used to detect movement.
Most arthropods possess ocelli
Refractive Cornea
Light rays enter the eye through the cornea. The cornea’s refracts the light rays through the pupil through which light enters the eye.
The iris works like an Aperture in a camera. It has the ability to enlarge and shrink, depending on how much light is entering the eye.
The light rays pass through the eye’s lens which works like the lens in a camera, shortening and lengthening its width in order to focus light rays properly.
Cones are active at higher light levels (photopic vision).
Are capable of colour vision
Are responsible for high three-dimensional acuity.
Are sensitive to narrow range of wavelength of light and there are three different types: L, M and S. (Or RGB)
This provides human beings with Colour Vision
Optical illusions -
Stare at dot in the centre then when you feel your eyes adjust
Then look in this white Gap.
How did this work?
The eye’s photoreceptors identify colours and code them in terms our brain can understand.
The colour channels of grayscale, red and green and blue, which allow us to code colour in any environment.
When looking at a specific colour, the cells in the relating colour channel, increase in activity.
But, after a short while, the cells become tired and decline.
When you look at blue for a long period of time, you stimulate the cells that are positively sensitive to blue
Then directing your gaze to a white wall, those cells don’t return to their resting activity.
Therefore, in the illusion our blue receptor cells become tired and decline, which stimulates the opposite hue, yellow and allows us to see a more natural skin tone and balances out the negative image to reveal the opposite.
The eye contains 3 types of cone cells, each containing a different pigment:
The L-cone detecting long wavelength light (peaking in the yellows – but also responsible for reds).
The M-cone detecting medium wavelength light (peaking in the greens).
The S-cone which detects short wavelength light (peaking with blue).
The most common types of colour deficiency are caused when one or more of these types of cone cells are weakened causing an inability to discriminate between different hues of colour.
The most common colour hues discriminated are between red/green and blue/yellow.
ISHIHARA Tests
Looks as colour blindness with numbers.
Camera vs Eyes: Similarities
Image focusing: Human and camera lenses both focus an inverted image onto a light-sensitive surface. In the case of a camera, it’s focused onto film or a sensor chip. In your eyes, the light-sensitive surface is the retina on the inside of your eyeball.
Light adjustment: Both the eye and a camera can adjust the quantity of lightentering. On a camera, it’s done with the aperture control built into your lens, whilst in your eye, it’s done by having a larger or smaller iris.
Subjective measuring of light: The human eye is a subjective device. Your eyes work in harmony with your brain to create the images you perceive. Your eyes adjust the focus (by bending the light through the lens in your eyeballs) and translating photons (light) into an electrical impulse your brain can process
Absolute measuring of light- A camera, is an absolute measurement device. It is measuring the light that hits a sensor, but the sensor is ‘dumb’, and the signals recorded need to be adjusted to suit the colour temperature of the light illuminating the scene.
Lens focus In camera: The lens moves closer/further from the film to focus.
Lens Focus in eye: The lens changes shape to focus. The muscles in your eyes change the actual shape of the lens inside your eyes.
Sensitivity to light in camera: A film in a camera is uniformly sensitive to light.
Sensitivity to light in eye: The human retina is not sensitive to light. Therefore, with respect to quality of image and capturing power, our eyes have a greater sensitivity in dark locations than a typical camera.
Our brains and Pareidolia
The Brain tries to make sense of the very little information it receives
Seeing recognisable objects or phenomena in otherwise random or unrelated objects or patterns is called Pareidolia.
Mainly the ability to see faces.
Moiré Patterns
Sometimes a pattern can interfere with the shape of the sensor within a camera, which can mean moiré pattens can emerge even when only one pattern is present.
