How Many Megapixels Can the Human Eye See

CAMERAS vs. THE HUMAN EYE

Why tin can't I just betoken my camera at what I'm seeing and record that? It's a seemingly simple question. It'south also 1 of the most complicated to answer, and requires delving into not simply how a camera records light, but also how and why our eyes work the way they do. Tackling such questions can reveal surprising insights near our everyday perception of the globe — in addition to making one a better photographer.

INTRODUCTION

Our optics are able to await around a scene and dynamically adjust based on subject thing, whereas cameras capture a single notwithstanding image. This trait accounts for many of our normally understood advantages over cameras. For example, our optics can compensate as we focus on regions of varying brightness, tin look around to embrace a broader angle of view, or can alternately focus on objects at a variety of distances.

However, the end event is akin to a video camera — not a stills camera — that compiles relevant snapshots to grade a mental image. A quick glance by our eyes might be a fairer comparison, but ultimately the uniqueness of our visual system is unavoidable because:

What we really run into is our listen's reconstruction of objects based on input provided by the optics — non the bodily calorie-free received by our eyes.

Skeptical? Near are — at to the lowest degree initially. The examples beneath evidence situations where one'due south mind can be tricked into seeing something different than one's eyes:

Simulated Color

Mach Bands

Fake Color: Motion your mouse onto the corner of the image and stare at the central cross. The missing dot volition rotate around the circle, but after a while this dot will appear to be green — even though no green is actually present in the image.

Mach Bands: Motility your mouse on and off of the image. Each of the bands will announced slightly darker or lighter near its upper and lower edges — even though each is uniformly gray.

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Withal, this shouldn't discourage the states from comparison our optics and cameras! Under many weather a fair comparing is all the same possible, but simply if we take into consideration both what nosotros're seeing and how our mind processes this information. Subsequent sections will endeavour to distinguish the two whenever possible.

OVERVIEW OF DIFFERENCES

This tutorial groups comparisons into the following visual categories:

1. Bending of View
2. Resolution & Detail
3. Sensitivity & Dynamic Range

The to a higher place are often understood to be where our eyes and cameras differ the most, and are usually also where in that location is the most disagreement. Other topics might include depth of field, stereo vision, white balancing and color gamut, only these won't be the focus of this tutorial.

1. Angle OF VIEW

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:

Unfortunately our optics aren't as straightforward. Although the human eye has a focal length of approximately 22 mm, this is misleading because (i) the back of our optics are curved, (ii) the periphery of our visual field contains progressively less detail than the center, and (iii) the scene we perceive is the combined result of both eyes.

Each eye individually has anywhere from a 120-200° angle of view, depending on how strictly one defines objects as existence "seen." Similarly, the dual heart overlap region is effectually 130° — or nearly as wide every bit a fisheye lens. However, for evolutionary reasons our extreme peripheral vision is only useful for sensing move and big-scale objects (such equally a lion pouncing from your side). Furthermore, such a wide bending would appear highly distorted and unnatural if information technology were captured by a camera.

Left Eye	Dual Center Overlap	Right Eye

Our primal angle of view — around twoscore-60° — is what nigh impacts our perception. Subjectively, this would correspond with the bending over which you could recall objects without moving your eyes. Incidentally, this is close to a 50 mm "normal" focal length lens on a total frame camera (43 mm to be precise), or a 27 mm focal length on a camera with a 1.6X crop factor. Although this doesn't reproduce the full angle of view at which we see, it does correspond well with what nosotros perceive as having the all-time trade-off betwixt unlike types of distortion:

Likewise wide an bending of view and the relative sizes of objects are exaggerated, whereas as well narrow an angle of view means that objects are all nearly the same relative size and y'all lose the sense of depth. Extremely wide angles also tend to make objects nigh the edges of the frame appear stretched.

(if captured by a standard/rectilinear camera lens)

By comparison, even though our eyes capture a distorted wide angle image, nosotros reconstruct this to class a 3D mental image that is seemingly distortion-free.

2. RESOLUTION & Item

Most current digital cameras have v-twenty 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 centre is able to resolve the equivalent of a 52 megapixel camera (assuming a 60° bending of view).

Even so, such calculations are misleading. Only our central vision is xx/xx, so nosotros never actually resolve that much detail in a single glance. Away from the center, our visual ability decreases dramatically, such that by simply 20° off-eye our optics resolve only one-tenth as much detail. At the periphery, we only find large-calibration contrast and minimal colour:

Qualitative representation of visual detail using a unmarried glance of the eyes.

Taking the in a higher place into account, a single glance by our optics is therefore just capable of perceiving detail comparable to a 5-15 megapixel camera (depending on one's eyesight). All the same, our listen doesn't actually remember images pixel past pixel; information technology instead records memorable textures, color and contrast on an paradigm past paradigm basis.

In order to gather a detailed mental epitome, our eyes therefore focus on several regions of interest in rapid succession. This effectively paints our perception:

The end consequence is a mental image whose detail has effectively been prioritized based on interest. This has an of import only often overlooked implication for photographers: even if a photograph approaches the technical limits of camera detail, such particular ultimately won't count for much if the imagery itself isn't memorable.

Other important differences with how our optics resolve detail include:

Asymmetry. Each eye is more capable of perceiving item beneath our line of sight than higher up, and their peripheral vision is also much more sensitive in directions away from the olfactory organ than towards it. Cameras record images nigh perfectly symmetrically.

Depression-Light Viewing. In extremely low lite, such as under moonlight or starlight, our eyes actually begin to run across in monochrome. Under such situations, our fundamental vision also begins to depict less detail than but off-eye. Many astrophotographers are aware of this, and use it to their reward by staring but to the side of a dim star if they want to be able to encounter information technology with their unassisted optics.

Subtle Gradations. Also much attending is often given to the finest detail resolvable, merely subtle tonal gradations are also important — and happen to be where our eyes and cameras differ the most. With a camera, enlarged detail is e'er easier to resolve — but counter-intuitively, enlarged item might actually become less visible to our eyes. In the example beneath, both images contain texture with the same amount of contrast, but this isn't visible in the paradigm to the right considering the texture has been enlarged.

Fine Texture
(barely visible)

→
Enlarged 16X

Coarse Texture
(no longer visible)

3. SENSITIVITY & DYNAMIC RANGE

Dynamic range* is one surface area where the eye is often seen as having a huge reward. If nosotros were to consider situations where our student opens and closes for different brightness regions, and so yes, our eyes far surpass the capabilities of a single camera image (and can have a range exceeding 24 f-stops). Even so, in such situations our centre 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), and then cameras fare much better. This would be like to looking at 1 region within a scene, letting our eyes adjust, and not looking anywhere else. In that instance, almost estimate that our eyes can see anywhere from 10-xiv f-stops of dynamic range, which definitely surpasses most compact cameras (v-7 stops), but is surprisingly similar to that of digital SLR cameras (8-11 stops).

On the other mitt, our eye's dynamic range also depends on brightness and subject area dissimilarity, then the above only applies to typical daylight conditions. With low-light star viewing our optics can approach an even higher instantaneous dynamic range, for instance.

*Quantifying Dynamic Range. The most commonly used unit for measuring dynamic range in photography is the f-stop, so nosotros'll stick with that here. This describes the ratio between the lightest and darkest recordable regions of a scene, in powers of two. A scene with a dynamic range of 3 f-stops therefore has a white that is 8X every bit vivid as its black (since ii³ = 2x2x2 = eight).

Photos on left (matches) and right (nighttime heaven) by lazlo and dcysurfer, respectively.

Sensitivity. This is another important visual characteristic, and describes the power to resolve very faint or fast-moving subjects. During vivid low-cal, modernistic cameras are amend at resolving fast moving subjects, as exemplified by unusual-looking high-speed photography. This is often fabricated possible past camera ISO speeds exceeding 3200; the equivalent daylight ISO for the human being eye is even thought to be every bit low as 1.

Notwithstanding, under low-light conditions, our eyes become much more than sensitive (presuming that we let them adjust for 30+ minutes). Astrophotographers often estimate this as beingness near ISO 500-k; nevertheless not as high every bit digital cameras, only close. On the other hand, cameras accept the advantage of existence able to have longer exposures to bring out fifty-fifty fainter objects, whereas our eyes don't encounter additional detail afterwards staring at something for more than almost ten-xv seconds.

CONCLUSIONS & Farther READING

One might argue that whether a camera is able to beat out the human being eye is inconsequential, because cameras require a unlike standard: they demand to make realistic-looking prints. A printed photograph doesn't know which regions the eye volition focus on, so every portion of a scene would demand to contain maximal detail — just in case that'southward where nosotros'll focus. This is especially true for large or closely viewed prints. Nevertheless, one could besides fence that it'south still useful to put a camera's capabilities in context.

Overall, most of the advantages of our visual organization stem from the fact that our listen is able to intelligently interpret the information from our eyes, whereas with a camera, all we have is the raw image. Even then, current digital cameras fare surprisingly well, and surpass our own eyes for several visual capabilities. The existent winner is the lensman who is able to intelligently assemble multiple camera images — thereby surpassing fifty-fifty our own mental image.

Please see the following for further reading on this topic:

• High Dynamic Range. How to extend the dynamic range of digital cameras using multiple exposures. Results tin can even exceed the homo eye.
• Graduated Neutral Density (GND) Filters. A technique for enhancing the advent of loftier contrast scenes similar to how nosotros class our mental image.
• Photo Stitching Digital Panoramas. A general give-and-take of using multiple photos to enhance the bending of view.

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Source: https://www.cambridgeincolour.com/tutorials/cameras-vs-human-eye.htm

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