File Name: difference between human eye and camera .zip
- OPTIK by/par VuePoint - Optik March / Mars 2016
- Lens (anatomy)
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- Comparison of the Human Eye to a Camera
The camera and the human eye have much more in common than just conceptual philosophy -- the eye captures images similar to the way the camera does. The anatomy of the camera bears more similarities to a biological eyeball than many would imagine, including the lens-like cornea and the film-like retina. Similarities like these give the camera the appearance of a robotic eye.
The structure and operation of the eye is very similar to an electronic camera, and it is natural to discuss them together. Both are based on two major components: a lens assembly, and an imaging sensor. The lens assembly captures a portion of the light emanating from an object, and focus it onto the imaging sensor. The imaging sensor then transforms the pattern of light into a video signal, either electronic or neural.
OPTIK by/par VuePoint - Optik March / Mars 2016
The structure and operation of the eye is very similar to an electronic camera, and it is natural to discuss them together. Both are based on two major components: a lens assembly, and an imaging sensor.
The lens assembly captures a portion of the light emanating from an object, and focus it onto the imaging sensor. The imaging sensor then transforms the pattern of light into a video signal, either electronic or neural.
Figure shows the operation of the lens. In this example, the image of an ice skater is focused onto a screen. The term focus means there is a one-to-one match of every point on the ice skater with a corresponding point on the screen. For example, consider a 1 mm? In bright light, there are roughly trillion photons of light striking this one square millimeter area each second. Depending on the characteristics of the surface, between 1 and 99 percent of these incident light photons will be reflected in random directions.
Only a small portion of these reflected photons will pass through the lens. For example, only about one-millionth of the reflected light will pass through a one centimeter diameter lens located 3 meters from the object.
These direction changes cause light expanding from a single point to return to a single point on the projection screen. All of the photons that reflect from the toe and pass through the lens are brought back together at the "toe" in the projected image.
In a similar way, a portion of the light coming from any point on the object will pass through the lens, and be focused to a corresponding point in the projected image. Figures and illustrate the major structures in an electronic camera and the human eye, respectively. Both are light tight enclosures with a lens mounted at one end and an image sensor at the other.
The camera is filled with air, while the eye is filled with a transparent liquid. Each lens system has two adjustable parameters: focus and iris diameter. If the lens is not properly focused, each point on the object will project to a circular region on the imaging sensor, causing the image to be blurry.
In the camera, focusing is achieved by physically moving the lens toward or away from the imaging sensor. In comparison, the eye contains two lenses, a bulge on the front of the eyeball called the cornea, and an adjustable lens inside the eye.
The cornea does most of the light refraction, but is fixed in shape and location. Adjustment to the focusing is accomplished by the inner lens, a flexible structure that can be deformed by the action of the ciliary muscles.
As these muscles contract, the lens flattens to bring the object into a sharp focus. In both systems, the iris is used to control how much of the lens is exposed to light, and therefore the brightness of the image projected onto the imaging sensor. The iris of the eye is formed from opaque muscle tissue that can be contracted to make the pupil the light opening larger.
The iris in a camera is a mechanical assembly that performs the same function. The parameters in optical systems interact in many unexpected ways. For example, consider how the amount of available light and the sensitivity of the light sensor affects the sharpness of the acquired image.
This is because the iris diameter and the exposure time are adjusted to transfer the proper amount of light from the scene being viewed to the image sensor. If more than enough light is available, the diameter of the iris can be reduced, resulting in a greater depth-of-field the range of distance from the camera where an object remains in focus.
A greater depth-of-field provides a sharper image when objects are at various distances. In addition, an abundance of light allows the exposure time to be reduced, resulting in less blur from camera shaking and object motion. Optical systems are full of these kinds of trade-offs. An adjustable iris is necessary in both the camera and eye because the range of light intensities in the environment is much larger than can be directly handled by the light sensors.
For example, the difference in light intensities between sunlight and moonlight is about one-million. The dynamic range of an electronic camera is typically to , defined as the largest signal that can be measured, divided by the inherent noise of the device.
Put another way, the maximum signal produced is 1 volt, and the rms noise in the dark is about 1 millivolt. Typical camera lenses have an iris that change the area of the light opening by a factor of about This results in a typical electronic camera having a dynamic range of a few hundred thousand.
Clearly, the same camera and lens assembly used in bright sunlight will be useless on a dark night. In comparison, the eye operates over a dynamic range that nearly covers the large environmental variations.
Surprisingly, the iris is not the main way that this tremendous dynamic range is achieved. From dark to light, the area of the pupil only changes by a factor of about The light detecting nerve cells gradually adjust their sensitivity to handle the remaining dynamic range. For instance, it takes several minutes for your eyes to adjust to the low light after walking into a dark movie theater.
One way that DSP can improve images is by reducing the dynamic range an observer is required to view. That is, we do not want very light and very dark areas in the same image. A reflection image is formed from two image signals: the two-dimensional pattern of how the scene is illuminated , multiplied by the two-dimensional pattern of reflectance in the scene.
This is where most of the image information is contained, such as where objects are located in the scene and what their surface characteristics are. In comparison, the illumination signal depends on the light sources around the objects, but not on the objects themselves. The illumination signal can have a dynamic range of millions, although 10 to is more typical within a single image.
The illumination signal carries little interesting information,. DSP can improve this situation by suppressing the illumination signal, allowing the reflectance signal to dominate the image.
The next chapter presents an approach for implementing this algorithm. The light sensitive surface that covers the rear of the eye is called the retina. As shown in Fig. In nearly all animals, these layers are seemingly backward. That is, the light sensitive cells are in last layer, requiring light to pass through the other layers before being detected. There are two types of cells that detect light: rods and cones , named for their physical appearance under the microscope.
The rods are specialized in operating with very little light, such as under the nighttime sky. Vision appears very noisy in near darkness, that is, the image appears to be filled with a continually changing grainy pattern.
This results from the image signal being very weak, and is not a limitation of the eye. There is so little light entering the eye, the random detection of individual photons can be seen.
This is called statistical noise , and is encountered in all low-light imaging, such as military night vision systems.
Chapter 25 will revisit this topic. Since rods cannot detect color, low-light vision is in black and white. The cone receptors are specialized in distinguishing color, but can only operate when a reasonable amount of light is present.
There are three types of cones in the eye: red sensitive, green sensitive, and blue sensitive. This results from their containing different photopigments , chemicals that absorbs different wavelengths colors of light.
Figure shows the wavelengths of light that trigger each of these three receptors. This is called RGB encoding , and is how color information leaves the eye through the optic nerve. The human perception of color is made more complicated by neural processing in the lower levels of the brain. The RGB encoding is converted into another encoding scheme, where colors are classified as: red or green, blue or yellow, and light or dark.
RGB encoding is an important limitation of human vision; the wavelengths that exist in the environment are lumped into only three broad categories. In comparison, specialized cameras can separate the optical spectrum into hundreds or thousands of individual colors. For example, these might be used to classify cells as cancerous or healthy, understand the physics of a distant star, or see camouflaged soldiers hiding in a forest. Why is the eye so limited in detecting color? Apparently, all humans need for survival is to find a red apple, among the green leaves, silhouetted against the blue sky.
This results in the retina being composed of an array of roughly 10,? In comparison, the optic nerve only has about one-million nerve fibers that connect to these cells. On the average, each optic nerve fiber is connected to roughly light receptors through the connecting layer. In addition to consolidating information, the connecting layer enhances the image by sharpening edges and suppressing the illumination component of the scene.
This biological image processing will be discussed in the next chapter. Directly in the center of the retina is a small region called the fovea Latin for pit , which is used for high resolution vision see Fig. The fovea is different from the remainder of the retina in several respects. First, the optic nerve and interconnecting layers are pushed to the side of the fovea, allowing the receptors to be more directly exposed to the incoming light. This results in the fovea appearing as a small depression in the retina.
Second, only cones are located in the fovea, and they are more tightly packed that in the remainder of the retina. This absence of rods in the fovea explains why night vision is often better when looking to the side of an object, rather than directly at it.
Third, each optic nerve fiber is influenced by only a few cones, proving good localization ability. The fovea is surprisingly small. At normal reading distance, the fovea only sees about a 1 mm diameter area, less than the size of a single letter!
The resolution is equivalent to about a 20? Human vision overcomes the small size of the fovea by jerky eye movements called saccades. These abrupt motions allow the high resolution fovea to rapidly scan the field of vision for pertinent information.
In addition, saccades present the rods and cones with a continually changing pattern of light. This is important because of the natural ability of the retina to adapt to changing levels of light intensity.
Light enters the eye through the cornea, the clear front surface of the eye, which acts like a camera lens. Parts of Human Eye and Their Functions Understanding the different parts of our eye can help you understand how you see and what you can do to help keep the eye functioning properly. It provides most of the refraction of light. Ciliary muscle located on each human eye connects the choroid with the iris. The near point of an eye is also known as the least distance of distinct vision. The near point of a normal human eye is at a distance of 25 centimetres from the eye. The nearest point up to which the eye can see an object clearly without any strain, is called the near point of the eye.
The human eye is a paired sense organ that reacts to light and allows vision. Rod and cone cells in the retina are photoreceptive cells which are able to detect visible light and convey this information to the brain. Eyes signal information which is used by the brain to elicit the perception of color, shape, depth, movement, and other features. The eye is part of the sensory nervous system. Similar to the eyes of other mammals , the human eye's non-image-forming photosensitive ganglion cells in the retina receive light signals which affect adjustment of the size of the pupil, regulation and suppression of the hormone melatonin , and entrainment of the circadian rhythm. Humans have two eyes, situated on the left and the right of the face. The eyes sit in bony cavities called the orbits , in the skull.
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The human eye is often compared to a camera. But how similar are they? We all know that the cornea has a high refractive power. It bends incident light by 43 diopters on average, while weighing as much as a feather with its 0. It goes without saying that the front camera lens is not as lightweight or powerful, plus the cornea repairs itself when scratched!
The lens is a transparent biconvex structure in the eye that, along with the cornea , helps to refract light to be focused on the retina. By changing shape, it functions to change the focal length of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. This adjustment of the lens is known as accommodation see also below. Accommodation is similar to the focusing of a photographic camera via movement of its lenses.
Роскошной рыжеволосой девицей.
Comparison of the Human Eye to a Camera
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light sensors sensing the image. A key difference between the human eye and the camera is in how the focusing is done. In your own eyes, when you look from.
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