Retinas, film, and imaging sensor chips all have one other thing in common. They all receive an inverted (upside-down) version of the image. Why? The lens in both an eye and a camera is convex, or curved outwards. When light hits a convex object, it refracts. This flips the image upside-down.
This is because your brain steps in to help your eyes. It knows the world is supposed to be right side up. So it flips the image over again. Digital cameras are programmed to make the correction on their own. Non-digital cameras contain a prism or mirror that flips the image so it appears right side up. Film is transparent so you can view the images on it the right way around.
Is the eye similar to a camera
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Cameras also have photoreceptors. But they only have one type. Cameras respond to red, blue and green light using filters placed on top of their photoreceptors. The photoreceptors in a camera are evenly distributed across the lens. In the human eye, however, the cones are concentrated at the centre of the retina. There are no rods at all at the centre of the retina.
Many people ask their eye doctors in Miami about the main differences and similarities between cameras and the human eye. In fact, there are plenty of similarities between the human eye and a camera. There are many internal functions that work just the same, and there are also some parts of a camera that perform just as structures of the eye do. However, the human eye is obviously more efficient than any camera that has been produced as of yet. People who are wondering how similar the human eye is to a camera will likely ask their Miami eye doctor this question on their next visit.
Those who are wondering just how similar a camera is to the human eye will be shocked to find out the functions of a camera that work just the same. Your optometrist in Miami Beach will be able to explain which parts of the camera work like parts of the human eye.
The retina is an enormously powerful tool. It sorts through massive amounts of data while operating on only a fraction of the power that a conventional digital camera and computer would require to do the same task.
The pixels in the DVS also mimic the way an individual eye neuron will calibrate itself to a particular location: that cell and those responsible for another area will respond to incoming data in slightly different ways, so one neuron might be very sensitive to input while another takes more stimulation to fire. Similarly, each pixel of the DVS adjusts its own exposure. This allows the DVS to handle uneven lighting conditions, though it also requires enormous pixels that are 10 times the size of those in a modern cell-phone camera.
Our eyes are able to look around a scene and dynamically adjust based on subject matter, whereas cameras capture a single still image. This trait accounts for many of our commonly understood advantages over cameras. For example, our eyes can compensate as we focus on regions of varying brightness, can look around to encompass a broader angle of view, or can alternately focus on objects at a variety of distances.
However, this shouldn't discourage us from comparing our eyes and cameras! Under many conditions a fair comparison is still possible, but only if we take into consideration both what we're seeing and how our mind processes this information. Subsequent sections will try to distinguish the two whenever possible.
The above are often understood to be where our eyes and cameras differ the most, and are usually also where there is the most disagreement. Other topics might include depth of field, stereo vision, white balancing and color gamut, but these won't be the focus of this tutorial.
With cameras, this is determined by the focal length of the lens (along with the sensor size of the camera). For example, a telephoto lens has a longer focal length than a standard portrait lens, and thus encompasses a narrower angle of view:
Most current digital cameras have 5-20 megapixels, which is often cited as falling far short of our own visual system. This is based on the fact that at 20/20 vision, the human eye is able to resolve the equivalent of a 52 megapixel camera (assuming a 60 angle of view).
Taking the above into account, a single glance by our eyes is therefore only capable of perceiving detail comparable to a 5-15 megapixel camera (depending on one's eyesight). However, our mind doesn't actually remember images pixel by pixel; it instead records memorable textures, color and contrast on an image by image basis.
The end result is a mental image whose detail has effectively been prioritized based on interest. This has an important but often overlooked implication for photographers: even if a photograph approaches the technical limits of camera detail, such detail ultimately won't count for much if the imagery itself isn't memorable.
Dynamic range* is one area where the eye is often seen as having a huge advantage. If we were to consider situations where our pupil opens and closes for different brightness regions, then yes, our eyes far surpass the capabilities of a single camera image (and can have a range exceeding 24 f-stops). However, in such situations our eye is dynamically adjusting like a video camera, so this arguably isn't a fair comparison.
If we were to instead consider our eye's instantaneous dynamic range (where our pupil opening is unchanged), then cameras fare much better. This would be similar to looking at one region within a scene, letting our eyes adjust, and not looking anywhere else. In that case, most estimate that our eyes can see anywhere from 10-14 f-stops of dynamic range, which definitely surpasses most compact cameras (5-7 stops), but is surprisingly similar to that of digital SLR cameras (8-11 stops).
Sensitivity. This is another important visual characteristic, and describes the ability to resolve very faint or fast-moving subjects. During bright light, modern cameras are better at resolving fast moving subjects, as exemplified by unusual-looking high-speed photography. This is often made possible by camera ISO speeds exceeding 3200; the equivalent daylight ISO for the human eye is even thought to be as low as 1.
However, under low-light conditions, our eyes become much more sensitive (presuming that we let them adjust for 30+ minutes). Astrophotographers often estimate this as being near ISO 500-1000; still not as high as digital cameras, but close. On the other hand, cameras have the advantage of being able to take longer exposures to bring out even fainter objects, whereas our eyes don't see additional detail after staring at something for more than about 10-15 seconds.
Structural similarities between human and octopus eyes. Even though there are some differences between human and octopus eyes, each of the tissues such as eyelid, cornea, pupil, iris, ciliary muscle, lens, retina, and optic nerve/ganglion corresponds well to each other. The octopus eye forms from an epidermal placode through a series of successive infoldings, whereas the human eye forms from the neural plate and induces the overlying epidermis to form the lens (Harris 1997). The differences in developmental processes between human and octopus are explained in the same reference (Harris 1997). This figure was modified with permission from Sinauer Associates, Inc., 1990 (Brusca and Brusca 1990).
A scheme to illustrate the number of genes derived from the ancestral gene set of the camera eye in each species lineage. This topology has been accepted by many molecular biologists and developmental biologists (Schmidt-Rhaesa 1998; Adoutte et al. 2000; Girbet et al. 2000; Morris 2000; Peterson et al. 2000, 2001). The number of conserved genes is shown below each species name. The numbers in italic represent the number of gene loss in each branch. (*) The number of the ancestral gene set that was obtained from the estimation of homologous genes between octopus-eye ESTs and the genomes of deuterostomes and out-group bilaterian species. (**) The number of conserved genes shared among the ancestral gene set and the genomes of the mosquito and fly as the representatives of conserved genes in insects. (***) The union of conserved genes in Fugu, mice, and humans as representatives of conserved genes in vertebrates.
From the viewpoint of key genes in eye development, Pax6 has not been found in the octopus. However, a six3 homolog was present in the set of octopus-eye ESTs that were identified in this study. The six3 gene is involved in a downstream part of the developmental pathway of eye formation controlled by Pax6. Therefore, it is likely that the Pax6-pathway for eye formation is conserved in the octopus. These observations imply that the gene expression patterns in both the eyes of humans and octopuses are remarkably similar. In other words, the common ancestor of octopus and human had not only the common master regulator, Pax6, but also the ancestral gene set for the camera eyes.
Moreover, the numbers of conserved genes in insects and nematodes were less than those in vertebrates; nevertheless, insects and nematodes are more closely related to octopuses than are vertebrates. This indicates that insects and nematodes have lost many more genes in their lineages than humans have. On the other hand, the number of conserved genes in tunicates is larger than those in insects or worms, even though they also do not possess the camera eye structure. One of the possible reasons is that insects or nematodes have lost the genes possibly unimportant for their body plans, because these organisms are known to tend to lose the genes unless they are important (Fig. 3). As we estimated 1019 genes for ancestral genes for the camera eye, more than 760 genes were conserved in flies or worms. This conservation in flies or worms suggests that not all of these genes were specific to the camera eye. In the case of conserved genes in flies or worms, it is possible that these genes derived from the common ancestral gene set can be used in other organs and cells such as the photo-sensory system. 2ff7e9595c
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