What Is A Good Dynamic Range

By | 13/11/2022

DYNAMIC RANGE IN DIGITAL PHOTOGRAPHY

Dynamic range in photography describes the ratio betwixt the maximum and minimum measurable light intensities (white and black, respectively). In the real world, one never encounters true white or black — but varying degrees of light source intensity and bailiwick reflectivity. Therefore the concept of dynamic range becomes more than complicated, and depends on whether you are describing a capture device (such as a camera or scanner), a display device (such every bit a print or computer brandish), or the discipline itself.

digital imaging chain

But equally with color management, each device inside the in a higher place imaging chain has their own dynamic range. In prints and computer displays, nothing can go brighter than paper white or a maximum intensity pixel, respectively. In fact, another device not shown above is our eyes, which likewise have their ain dynamic range. Translating paradigm data between devices may therefore touch on how that image is reproduced. The concept of dynamic range is therefore useful for relative comparisons between the bodily scene, your camera, and the image on your screen or in the last impress.

INFLUENCE OF Lite: ILLUMINANCE & REFLECTIVITY

Light intensity can be described in terms of incident and reflected light; both contribute to the dynamic range of a scene (see tutorial on “camera metering and exposure”).

Scenes with high variation in reflectivity, such as those containing black objects in addition to strong reflections, may really have a greater dynamic range than scenes with large incident light variation. Photography under either scenario can easily exceed the dynamic range of your camera — particularly if the exposure is not spot on.

Authentic measurement of calorie-free intensity, or luminance, is therefore critical when assessing dynamic range. Here we use the term illuminance to specify only incident light. Both illuminance and luminance are typically measured in candelas per foursquare meter (cd/one thousand2). Approximate values for commonly encountered light sources are shown beneath.

Here we see the vast variation possible for incident light, since the above diagram is scaled to powers of ten. If a scene were unevenly illuminated past both direct and obstructed sunlight, this alone tin profoundly increase a scene’s dynamic range (as apparent from the coulee dusk example with a partially-lit cliff face).

DIGITAL CAMERAS

Although the meaning of dynamic range for a existent-world scene is only the ratio between lightest and darkest regions (dissimilarity ratio), its definition becomes more complicated when describing measurement devices such as digital cameras and scanners. Recall from the tutorial on digital camera sensors that light is measured at each pixel in a cavity or well (photosite). Each photosite’s size, in improver to how its contents are measured, make up one’s mind a digital camera’south dynamic range.


Black Level
(Limited by Noise)


White Level
(Saturated Photosite)


Darker White Level
(Low Capacity Photosite)

Photosites can be idea of as buckets which concur photons as if they were h2o. Therefore, if the bucket becomes likewise full, it volition overflow. A photosite which overflows is said to have go saturated, and is therefore unable to discern between boosted incoming photons — thereby defining the photographic camera’southward white level. For an ideal camera, its contrast ratio would therefore be only the number of photons it could comprise within each photosite, divided by the darkest measurable light intensity (i photon). If each held 1000 photons, so the dissimilarity ratio would be 1000:1. Since larger photosites can contain a greater range of photons,
dynamic range is generally college for digital SLR cameras compared to compact cameras
(due to larger pixel sizes).

Technical Annotation: In some digital cameras, there is an extended low ISO setting which produces less noise, but also decreases dynamic range. This is considering the setting in effect overexposes the image by a full f-end, but then afterward truncates the highlights — thereby increasing the light point. An example of this is many of the Canon cameras, which have an ISO-fifty speed beneath the ordinary ISO-100.

In reality, consumer cameras cannot count individual photons. Dynamic range is therefore limited by the darkest tone where texture can no longer be discerned; we call this the black level. The black level is express past how accurately each photosite tin can exist measured, and is therefore express in darkness by image racket. Therefore,
dynamic range mostly increases for lower ISO speeds and cameras with less measurement noise.

Techncal Note: Fifty-fifty if a photosite could count individual photons, it would withal be express by photon noise. Photon noise is created by the statistical variation in arrival of photons, and therefore represents a theoretical minimum for noise. Total noise represents the sum of photon dissonance and read-out noise.

Overall, the dynamic range of a digital camera can therefore be described as the ratio of maximum light intensity measurable (at pixel saturation), to minimum light intensity measurable (above read-out noise).
The most commonly used unit for measuring dynamic range in digital cameras is the f-end, which describes full light range by powers of 2. A contrast ratio of 1024:1 could therefore also be described every bit having a dynamic range of x f-stops (since 210
= 1024). Depending on the application, each unit f-stop may besides be described as a “zone” or “eV.”

SCANNERS

Scanners are discipline to the aforementioned saturation:noise criterion equally for dynamic range in digital cameras, except it is instead described in terms of density (D). This is useful considering it is conceptually similar to how pigments create tones in printed media, as shown beneath.

The overall dynamic range in terms of density is therefore the maximum pigment density (Dmax), minus the minimum pigment density (Dmin). Different powers of ii for f-stops, density is measured using powers of x (just equally the Richter scale for earthquakes). A density of 3.0 therefore represents a contrast ratio of m:one (since 103.0
= 1000).

Instead of listing total density (D), scanner manufacturer’s typically list just the Dmax
value, since Dmax
– Dmin

is approximately equal to Dmax. This is because unlike with digital cameras, a scanner has total control over it’southward light source, ensuring that minimal photosite saturation occurs.

For loftier pigment density, the same noise constraints apply to scanners as digital cameras (since they both use an array of photosites for measurement). Therefore the measurable Dmax
is too adamant by the noise present during read-out of the light signal.

COMPARISON

Dynamic range varies so greatly that it is ordinarily measured on a logarithmic scale, like to how vastly dissimilar convulsion intensities are all measured on the same Richter scale. Here nosotros show the maximum measurable (or reproducible) dynamic range for several devices in terms any preferred mensurate (f-stops, density and contrast ratio). Motion your mouse over each of the options below to compare these.

Select Mensurate for Dynamic Range:
f-stops Density Contrast Ratio


Select Types to Display Above:
Printed Media Scanners Digital Cameras Display Devices

Note the huge discrepancy between reproducible dynamic range in prints, and that measurable past scanners and digital cameras. For a comparing with real-globe dynamic range in a scene, these vary from approximately 3 f-stops for a cloudy day with nearly fifty-fifty reflectivity, to 12+ f-stops for a sunny 24-hour interval with highly uneven reflectivity.

Care should be taken when interpreting the above numbers; existent-globe dynamic range is a strong part of ambient calorie-free for prints and display devices. Prints not viewed under adequate light may not give their full dynamic range, while display devices require near consummate darkness to realize their total potential — especially for plasma displays. Finally, these values are rough approximations only; actual values depend on age of device, model generation, price range, etc.

Be warned that dissimilarity ratios for display devices are often greatly exaggerated, as there is no manufacturer standard for listing these. Dissimilarity ratios in backlog of 500:1 are oft but the outcome of a very dark black point, instead of a brighter white point. For this reason attention should exist paid to both contrast ratio and luminosity. High contrast ratios (without a correspondingly higher luminosity) can be completely negated by fifty-fifty ambient candle light.

THE HUMAN Heart

The human being eye tin actually perceive a greater dynamic range than is ordinarily possible with a camera. If nosotros were to consider situations where our educatee opens and closes for varying lite, our eyes tin see over a range of nigh 24 f-stops.

On the other hand, for accurate comparisons with a single photo (at abiding aperture, shutter and ISO), nosotros tin can merely consider the instantaneous dynamic range (where our student opening is unchanged). This would be similar to looking at one region within a scene, letting our optics adjust, and not looking anywhere else. For this scenario there is much disagreement, because our eye’southward sensitivity and dynamic range actually change depending on effulgence and contrast. Most estimate anywhere from 10-xiv f-stops.

The trouble with these numbers is that our eyes are extremely adaptable. For situations of extreme low-light star viewing (where our eyes accept adjusted to use rod cells for night vision), our optics arroyo fifty-fifty college instantaneous dynamic ranges (meet tutorial on “Color Perception of the Homo Heart”).

Flake DEPTH & MEASURING DYNAMIC RANGE

Fifty-fifty if one’s digital camera could capture a vast dynamic range, the precision at which light measurements are translated into digital values may limit usable dynamic range.
The workhorse which translates these continuous measurements into discrete numerical values is called the analog to digital (A/D) converter.
The accuracy of an A/D converter can be described in terms of bits of precision, similar to scrap depth in digital images, although care should exist taken that these concepts are non used interchangeably. The A/D converter is what creates values for the digital camera’south RAW file format.

Bit Precision
of Analog/Digital Converter
Dissimilarity Ratio Dynamic Range
f-stops Density
8 256:i eight two.iv
x 1024:1 10 iii.0
12 4096:1 12 3.6
fourteen 16384:1 14 4.2
xvi 65536:one 16 4.8

Note: To a higher place values are for A/D converter precision only, and should not be used to interpret results for eight and 16-bit epitome files. Furthermore, values shown are a theoretical maximum, assuming dissonance is not limiting, and this applies just to linear A/D converters.

As an example, 10-bits of tonal precision translates into a possible brightness range of 0-1023 (since 2ten
= 1024 levels).
Bold that each A/D converter number is proportional to actual image brightness
(meaning twice the pixel value represents twice the brightness), 10-bits of precision tin can only encode a contrast ratio of 1024:1.

Well-nigh digital cameras utilise a x to 14-chip A/D converter, and so their theoretical maximum dynamic range is 10-fourteen stops. However, this high fleck depth only helps minimize prototype posterization since total dynamic range is usually limited by noise levels. Similar to how a loftier bit depth image does not necessarily mean that image contains more colors, if a digital photographic camera has a high precision A/D converter it does non necessarily hateful information technology tin record a greater dynamic range. In event, dynamic range tin can be idea of every bit the height of a staircase whereas bit depth can be thought of every bit the number of steps.
In practice, the dynamic range of a digital camera does non fifty-fifty approach the A/D converter’s theoretical maximum; viii-12 stops is generally all i tin can expect from the camera.

INFLUENCE OF Epitome Type & TONAL Curve

Can digital epitome files actually record the total dynamic range of loftier-finish devices? There seems to exist much defoliation on the internet about the relevance of image bit depth on recordable dynamic range.

We first need to distinguish betwixt whether nosotros are speaking of recordable dynamic range, or displayable dynamic range. Fifty-fifty an ordinary 8-chip JPEG image file can feasibly record an infinite dynamic range — assuming that the right tonal bend is applied during RAW conversion (see tutorial on curves, under motivation: dynamic range), and that the A/D converter has the required bit precision. The problem lies in the usability of this dynamic range; if also few bits are spread over also great of a tonal range, and so this tin lead to epitome posterization.

On the other hand, displayable dynamic range depends on the gamma correction or tonal curve unsaid past the epitome file, or used by the video card and brandish device. Using a gamma of 2.two (standard for PC’s), information technology would be theoretically possible to encode a dynamic range of well-nigh 18 f-stops (see tutorial on gamma correction, to be added). Over again though, this would endure from severe posterization. The merely electric current standard solution for encoding a nearly infinite dynamic range (with no visible posterization) is to use high dynamic range (HDR) prototype files in Photoshop (or other supporting programme).






Source: https://www.cambridgeincolour.com/tutorials/dynamic-range.htm