High dynamic range imaging
Encyclopedia
In image processing
, computer graphics
, and photography
, high dynamic range imaging (HDRI or just HDR) is a set of techniques that allows a greater dynamic range between the lightest and darkest areas of an image than current standard digital imaging techniques or photographic methods. This wide dynamic range allows HDR images to more accurately represent the range of intensity levels found in real scenes, ranging from direct sunlight to faint starlight, and is often captured by way of a plurality of differently exposed pictures of the same subject matter.
The two main sources of HDR imagery are computer renderings and merging of multiple low-dynamic-range (LDR) or standard-dynamic-range (SDR) photographs. Tone-mapping
techniques, which reduce overall contrast to facilitate display of HDR images on devices with lower dynamic range, can be applied to produce images with preserved or exaggerated local contrast for artistic effect.
differences (known as stops) between the brightest and darkest parts of the image that show detail. An increase of one EV or one stop is a doubling of the amount of light.
High-dynamic-range photographs are generally achieved by capturing multiple standard photographs, often using exposure bracketing, and then merging them into an HDR image. Digital photographs are often encoded in a camera's raw image format
, because 8 bit JPEG
encoding doesn't offer enough values to allow fine transitions (and also introduces undesirable effects due to the lossy compression).
Any camera that allows manual over- or under-exposure of a photo can be used to create HDR images.
Some cameras have an auto exposure bracketing (AEB)
feature with a far greater dynamic range than others, from the 3 EV of the Canon EOS 40D
, to the 18 EV of the Canon EOS-1D Mark II
. As the popularity of this imaging technique grows, several camera manufactures are now offering built in HDR features. For example, the Pentax K-7
DSLR has an HDR mode which captures an HDR image and then outputs (only) a tone-mapped JPEG file. The Canon PowerShot G12 and Canon PowerShot S95
offer similar features in a smaller format. Even some smartphones now include HDR modes.
artifacts
such as banding
and jaggies
.
Photoshop users are familiar with the issues of low dynamic range today. With 8 bit channels, if you brighten an image, information is lost irretrievably: darkening the image after brightening does not restore the original appearance. Instead, all of the highlights appear flat and washed out. One must work in a carefully planned work-flow to avoid this problem.
When digitizing photographic material with a scanner
, the scanner has to be able to capture the whole dynamic range of the original, or else details get lost. The manufacturer's declarations concerning the dynamic range of flatbed and film scanners are often slightly inaccurate and exaggerated.
Despite color negative having less dynamic range than slide, it actually captures considerably more dynamic range of the scene than does slide film. This dynamic range is simply compressed considerably.
can be divided into three aspects: geometric calibration, photometric
calibration and spectral calibration. For HDR reconstruction, the important aspects are photometric and spectral
calibrations.
that is important concerning colors reproduction. Inspired on the trichromatic base of the human eye, the standard solution adopted by industry is to use red, green, and blue filters, referred as RGB base, to sample the input light signal and also to reproduce the signal using light-based image emitters. This employs an additive color
model, as opposed to the subtractive color
model used with printers, paintings etc.
Photographic color films usually have three layers of emulsion
, each with a different spectral curve, sensitive to red, green, and blue light, respectively. The RGB spectral response of the film is characterized by spectral sensitivity
and spectral dye density curves.
a scene, trying to represent the whole dynamic range while retaining realistic color and contrast.
Images with too much tone mapping processing have their range over-compressed, creating a surreal low-dynamic-range rendering of a high-dynamic-range scene.
or radiance
that can be observed in the real world. This is different from traditional digital images, which represent colors that should appear on a monitor or a paper print. Therefore, HDR image formats are often called "scene-referred", in contrast to traditional digital images, which are "device-referred" or "output-referred". Furthermore, traditional images are usually encoded for the human visual system
(maximizing the visual information stored in the fixed number of bits), which is usually called "gamma encoding" or "gamma correction
". The values stored for HDR images are often gamma compressed
(power law) or logarithm
ically encoded, or floating-point linear values, since fixed-point
linear encodings are increasingly inefficient over higher dynamic ranges.
HDR images often use a higher number of bits per color channel
than traditional images to represent many more colors over a much wider dynamic range. 16-bit ("half precision") or 32-bit floating point
numbers are often used to represent HDR pixels. However, when the appropriate transfer function
is used, HDR pixels for some applications can be represented with as few as 10–12 bits for luminance and 8 bits for chrominance
without introducing any visible quantization artifacts.
was pioneered as early as the 1850s by Gustave Le Gray
to render seascapes showing both the sky and the sea. Such rendering was impossible at the time using standard techniques, the luminosity range being too extreme. Le Gray used one negative for the sky, and another one with a longer exposure for the sea, and combined the two in a single picture in positive.
. Wyckoff's detailed pictures of nuclear explosions appeared on the cover of Life magazine in the mid 1950s. Wyckoff implemented local neighborhood tone remapping to combine differently exposed film layers into one single image of greater dynamic range.
, from his 1954 photo essay
A Man of Mercy on Dr. Albert Schweitzer
and his humanitarian work in French Equatorial Africa. The image took 5 days to produce, in order to reproduce the tonal range of the scene, which ranges from a bright lamp (relative to the scene) to a dark shadow.
Ansel Adams
elevated dodging and burning to an art form. Many of his famous prints were manipulated in the darkroom with these two techniques. Adams wrote a comprehensive book on producing prints called The Print, which features dodging and burning prominently, in the context of his Zone System
.
With the advent of color photography, tone mapping in the darkroom was no longer possible, due to the specific timing required during the developing process of color film. Photographers looked to film manufacturers to design new film stocks with improved response over the years, or shot in black and white to use tone-mapping techniques.
RGBE image file format
which was the first (and still the most commonly used) HDR imaging file format.
Wyckoff's concept of neighborhood tone mapping was applied to video cameras by a group from the Technion in Israel led by Prof. Y.Y.Zeevi who filed for a patent on this concept in 1988. In 1993 the first commercial medical camera was introduced that performed real time capturing of multiple images with different exposures, and producing an HDR video image, by the same group.
Modern HDR imaging uses a completely different approach, based on making a high dynamic range luminance or light map using only global image operations (across the entire image), and then tone mapping
this result. Global HDR was first introduced in 1993 resulting in a mathematical theory of differently exposed pictures of the same subject matter that was published in 1995 by Steve Mann
and Rosalind Picard.
This method was developed to produce a high dynamic range image from a set of photograph
s taken with a range of exposures
. With the rising popularity of digital camera
s and easy-to-use desktop software, the term HDR is now popularly used to refer to this process. This composite technique is different from (and may be of lesser or greater quality than) the production of an image from a single exposure of a sensor that has a native high dynamic range. Tone mapping is also used to display HDR images on devices with a low native dynamic range, such as a computer screen.
developed and patented the global-HDR method for producing digital images having extended dynamic range at the MIT Media Laboratory. Mann's method involved a two-step procedure: (1) generate a single floating point image array by global-only image operations (operations that affect all pixels identically, without regard to their local neighborhoods); and then (2) convert this image array, using local neighborhood processing (tone-remapping, etc.), into an HDR image. The image array generated by the first step of Mann's process is called a "lightspace image", "lightspace picture", or "radiance map". Another benefit of global-HDR imaging is that it provides access to the intermediate light or radiance map, which has been used for computer vision, and other image processing operations.
.
in iOS version 4.1 on September 8th 2010
Modern movies have often been filmed with cameras featuring a higher dynamic range
, and legacy
movies can be upgraded even if manual intervention would be required for some frames (as this happened in the past with black&white films’ upgrade to color). Also, special effects, especially those in which real and synthetic footage are seamlessly mixed, require both HDR shooting and rendering. HDR video is also required in all applications in which capturing temporal aspects of changes in the scene is required with high accuracy. This is in particular important in monitoring of some industrial processes such as welding, predictive driver assistance systems in automotive industry, surveillance systems, to name just a few possible applications. HDR video can be also considered to speed up the image acquisition in all applications, in which a large number of static HDR images are required, as for example in image-based techniques in computer graphics
. Finally, with the spread of TV sets featuring enhanced dynamic range, broadcasting HDR video will be important, but may take a long time to actually occur due to standardization
issues. For this particular application, enhancing current LDR video signal to HDR by intelligent TV sets seems to be a more viable near-term solution.
Image processing
In electrical engineering and computer science, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame; the output of image processing may be either an image or, a set of characteristics or parameters related to the image...
, computer graphics
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....
, and photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
, high dynamic range imaging (HDRI or just HDR) is a set of techniques that allows a greater dynamic range between the lightest and darkest areas of an image than current standard digital imaging techniques or photographic methods. This wide dynamic range allows HDR images to more accurately represent the range of intensity levels found in real scenes, ranging from direct sunlight to faint starlight, and is often captured by way of a plurality of differently exposed pictures of the same subject matter.
The two main sources of HDR imagery are computer renderings and merging of multiple low-dynamic-range (LDR) or standard-dynamic-range (SDR) photographs. Tone-mapping
Tone mapping
Tone mapping is a technique used in image processing and computer graphics to map one set of colors to another in order to approximate the appearance of high dynamic range images in a medium that has a more limited dynamic range...
techniques, which reduce overall contrast to facilitate display of HDR images on devices with lower dynamic range, can be applied to produce images with preserved or exaggerated local contrast for artistic effect.
Photography
In photography, dynamic range is measured in EVExposure value
In photography, exposure value denotes all combinations of a camera's shutter speed and relative aperture that give the same exposure. In an attempt to simplify choosing among combinations of equivalent camera settings, the concept was developed by the German shutter manufacturer in the 1950s...
differences (known as stops) between the brightest and darkest parts of the image that show detail. An increase of one EV or one stop is a doubling of the amount of light.
| Device | Stops | Contrast |
|---|---|---|
| LCD display | 9.5 | 700:1 (250:1 - 1750:1) |
| DSLR camera (Canon EOS-1D Mark II Canon EOS-1D Mark II The EOS 1D Mark II is a professional 8.2 megapixel digital single lens reflex camera camera body produced by Canon. The EOS 1D Mark II is the successor of the EOS 1D.-Features:The EOS 1D Mark II features:* 28.7 × 19.1 mm CMOS sensor... ) |
11 | 2048:1 |
| Print film | 7 | 128:1 |
| Human eye | 10–14 | 1024:1 – 16384:1 |
High-dynamic-range photographs are generally achieved by capturing multiple standard photographs, often using exposure bracketing, and then merging them into an HDR image. Digital photographs are often encoded in a camera's raw image format
RAW image format
A camera raw image file contains minimally processed data from the image sensor of either a digital camera, image scanner, or motion picture film scanner. Raw files are so named because they are not yet processed and therefore are not ready to be printed or edited with a bitmap graphics editor...
, because 8 bit JPEG
JPEG
In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
encoding doesn't offer enough values to allow fine transitions (and also introduces undesirable effects due to the lossy compression).
Any camera that allows manual over- or under-exposure of a photo can be used to create HDR images.
Some cameras have an auto exposure bracketing (AEB)
Autobracketing
Autobracketing is a feature of some more advanced cameras, whether film or digital cameras, particularly single-lens reflex cameras, where the camera will take several successive shots with slightly different settings. Later, the best-looking pictures can be picked from the batch...
feature with a far greater dynamic range than others, from the 3 EV of the Canon EOS 40D
Canon EOS 40D
The Canon EOS 40D is a 10.1-megapixel semi-professional digital single-lens reflex camera. It was initially announced on August 20, 2007 and was released at the end of that month. It is the successor of the Canon EOS 30D, and is succeeded by the EOS 50D. It can accept EF and EF-S lenses...
, to the 18 EV of the Canon EOS-1D Mark II
Canon EOS-1D Mark II
The EOS 1D Mark II is a professional 8.2 megapixel digital single lens reflex camera camera body produced by Canon. The EOS 1D Mark II is the successor of the EOS 1D.-Features:The EOS 1D Mark II features:* 28.7 × 19.1 mm CMOS sensor...
. As the popularity of this imaging technique grows, several camera manufactures are now offering built in HDR features. For example, the Pentax K-7
Pentax K-7
The Pentax K-7 is a 14.6-megapixel digital single-lens reflex camera, announced on 20 May 2009. This is the first new flagship model released by Pentax since its merger with Hoya Corporation on 31 March 2008.- Features :...
DSLR has an HDR mode which captures an HDR image and then outputs (only) a tone-mapped JPEG file. The Canon PowerShot G12 and Canon PowerShot S95
Canon PowerShot S95
The Canon PowerShot S95 is a high-end 10.0 megapixel compact digital camera announced and released in 2010. It was designed as the successor to the Canon PowerShot S90 in the S series of the Canon PowerShot line of cameras....
offer similar features in a smaller format. Even some smartphones now include HDR modes.
Editing
Of all imaging tasks, editing is the one that demands the highest dynamic range. Editing operations need high precision to avoid aliasingAliasing
In signal processing and related disciplines, aliasing refers to an effect that causes different signals to become indistinguishable when sampled...
artifacts
Digital artifact
A digital artifact is any undesired alteration in data introduced in a digital process by an involved technique and/or technology.-Possible causes:...
such as banding
Colour banding
Colour banding is a problem of inaccurate colour presentation in computer graphics. While in 24 bit colour modes, 8 bits per channel should be enough to render images in the full visible spectrum, in some cases there is a risk of producing abrupt changes between shades of the same colour...
and jaggies
Jaggies
"Jaggies" is the informal name for artifacts in raster images, most frequently from aliasing, which in turn is often caused by non-linear mixing effects producing high-frequency components and/or missing or poor anti-aliasing filtering prior to sampling....
.
Photoshop users are familiar with the issues of low dynamic range today. With 8 bit channels, if you brighten an image, information is lost irretrievably: darkening the image after brightening does not restore the original appearance. Instead, all of the highlights appear flat and washed out. One must work in a carefully planned work-flow to avoid this problem.
Scanning film
In contrast to digital photographs, color negatives and slides consist of multiple film layers that respond to light differently. As a consequence, transparent originals (especially positive slides) feature a very high dynamic range.| Material | Dynamic Range (F stops) | Object Contrast |
|---|---|---|
| photograph | 5 | 1:32 |
| color negative | 8 | 1:256 |
| positive slide | 12 | 1:4096 |
When digitizing photographic material with a scanner
Image scanner
In computing, an image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop scanner where the document is placed on a glass...
, the scanner has to be able to capture the whole dynamic range of the original, or else details get lost. The manufacturer's declarations concerning the dynamic range of flatbed and film scanners are often slightly inaccurate and exaggerated.
Despite color negative having less dynamic range than slide, it actually captures considerably more dynamic range of the scene than does slide film. This dynamic range is simply compressed considerably.
Camera characteristics
The characteristics of a camera need to be taken into account when reconstructing high dynamic range images. These characteristics are mainly related to gamma curves, sensor resolution, and noise.Camera calibration
Camera calibrationCalibration
Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device....
can be divided into three aspects: geometric calibration, photometric
Photometry (optics)
Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy in terms of absolute power; rather, in photometry, the radiant power at each wavelength is weighted by...
calibration and spectral calibration. For HDR reconstruction, the important aspects are photometric and spectral
Visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
calibrations.
Color reproduction
Light sensors and emitters try to mimic a scene's light signal concerning human perception; it is the human perceptionPerception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
that is important concerning colors reproduction. Inspired on the trichromatic base of the human eye, the standard solution adopted by industry is to use red, green, and blue filters, referred as RGB base, to sample the input light signal and also to reproduce the signal using light-based image emitters. This employs an additive color
Additive color
An additive color model involves light emitted directly from a source or illuminant of some sort. The additive reproduction process usually uses red, green and blue light to produce the other colors. Combining one of these additive primary colors with another in equal amounts produces the...
model, as opposed to the subtractive color
Subtractive color
A subtractive color model explains the mixing of paints, dyes, inks, and natural colorants to create a full range of colors, each caused by subtracting some wavelengths of light and reflecting the others...
model used with printers, paintings etc.
Photographic color films usually have three layers of emulsion
Emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
, each with a different spectral curve, sensitive to red, green, and blue light, respectively. The RGB spectral response of the film is characterized by spectral sensitivity
Spectral sensitivity
Spectral sensitivity is the relative efficiency of detection, of light or other signal, as a function of the frequency or wavelength of the signal....
and spectral dye density curves.
Contrast reduction
HDR images can easily be represented on common LDR devices, such as computer monitors and photographic prints, by simply reducing the contrast, just as all image editing software is capable of doing.Clipping and compressing dynamic range
Scenes with high dynamic ranges are often represented on LDR devices by cropping the dynamic range, cutting off the darkest and brightest details, or alternatively with an S conversion curve that compresses contrast progressively and more aggressively in the highlights and shadows while leaving the middle portions of the contrast range relatively unaffected.Tone mapping
Tone mapping reduces the dynamic range, or contrast ratio, of the entire image, while retaining localized contrast (between neighboring pixels), tapping into research on how the human eye and visual cortex perceivePerception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
a scene, trying to represent the whole dynamic range while retaining realistic color and contrast.
Images with too much tone mapping processing have their range over-compressed, creating a surreal low-dynamic-range rendering of a high-dynamic-range scene.
Comparison with traditional digital images
Information stored in high-dynamic-range images typically corresponds to the physical values of luminanceLuminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
or radiance
Radiance
Radiance and spectral radiance are radiometric measures that describe the amount of radiation such as light or radiant heat that passes through or is emitted from a particular area, and falls within a given solid angle in a specified direction. They are used to characterize both emission from...
that can be observed in the real world. This is different from traditional digital images, which represent colors that should appear on a monitor or a paper print. Therefore, HDR image formats are often called "scene-referred", in contrast to traditional digital images, which are "device-referred" or "output-referred". Furthermore, traditional images are usually encoded for the human visual system
Visual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
(maximizing the visual information stored in the fixed number of bits), which is usually called "gamma encoding" or "gamma correction
Gamma correction
Gamma correction, gamma nonlinearity, gamma encoding, or often simply gamma, is the name of a nonlinear operation used to code and decode luminance or tristimulus values in video or still image systems...
". The values stored for HDR images are often gamma compressed
Gamma correction
Gamma correction, gamma nonlinearity, gamma encoding, or often simply gamma, is the name of a nonlinear operation used to code and decode luminance or tristimulus values in video or still image systems...
(power law) or logarithm
Logarithm
The logarithm of a number is the exponent by which another fixed value, the base, has to be raised to produce that number. For example, the logarithm of 1000 to base 10 is 3, because 1000 is 10 to the power 3: More generally, if x = by, then y is the logarithm of x to base b, and is written...
ically encoded, or floating-point linear values, since fixed-point
Fixed-point arithmetic
In computing, a fixed-point number representation is a real data type for a number that has a fixed number of digits after the radix point...
linear encodings are increasingly inefficient over higher dynamic ranges.
HDR images often use a higher number of bits per color channel
Channel (digital image)
Color digital images are made of pixels, and pixels are made of combinations of primary colors. A channel in this context is the grayscale image of the same size as a color image, made of just one of these primary colors. For instance, an image from a standard digital camera will have a red, green...
than traditional images to represent many more colors over a much wider dynamic range. 16-bit ("half precision") or 32-bit floating point
Floating point
In computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...
numbers are often used to represent HDR pixels. However, when the appropriate transfer function
Transfer function
A transfer function is a mathematical representation, in terms of spatial or temporal frequency, of the relation between the input and output of a linear time-invariant system. With optical imaging devices, for example, it is the Fourier transform of the point spread function i.e...
is used, HDR pixels for some applications can be represented with as few as 10–12 bits for luminance and 8 bits for chrominance
Chrominance
Chrominance is the signal used in video systems to convey the color information of the picture, separately from the accompanying luma signal . Chrominance is usually represented as two color-difference components: U = B' − Y' and V = R' − Y'...
without introducing any visible quantization artifacts.
1850
The idea of using several exposures to fix a too-extreme range of luminanceLuminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
was pioneered as early as the 1850s by Gustave Le Gray
Gustave Le Gray
Jean-Baptiste Gustave Le Gray has been called "the most important French photographer of the nineteenth century" because of his technical innovations in the still new medium of photography, his role as the teacher of other noted photographers, and the extraordinary imagination he brought to picture...
to render seascapes showing both the sky and the sea. Such rendering was impossible at the time using standard techniques, the luminosity range being too extreme. Le Gray used one negative for the sky, and another one with a longer exposure for the sea, and combined the two in a single picture in positive.
1930
High dynamic range imaging was originally developed in the 1930s and 1940s by Charles WyckoffCharles Wyckoff
Charles Wales Wyckoff was an American photographic innovator, a photochemist specializing in high speed photography, also noted today for his innovations in the field of high dynamic range imaging....
. Wyckoff's detailed pictures of nuclear explosions appeared on the cover of Life magazine in the mid 1950s. Wyckoff implemented local neighborhood tone remapping to combine differently exposed film layers into one single image of greater dynamic range.
Mid-century
Mid-century, manual tone mapping was particularly done using dodging and burning – selectively increasing or decreasing the exposure of regions of the photograph to yield better tonality reproduction. An excellent example is the photograph "Schweitzer at the Lamp" by W. Eugene SmithW. Eugene Smith
William Eugene Smith was an American photojournalist known for his refusal to compromise professional standards and his brutally vivid World War II photographs.- Life and work :...
, from his 1954 photo essay
Photo essay
A photo-essay is a set or series of photographs that are intended to tell a story or evoke a series of emotions in the viewer. A photo essay will often show pictures in deep emotional stages. Photo essays range from purely photographic works to photographs with captions or small notes to full text...
A Man of Mercy on Dr. Albert Schweitzer
Albert Schweitzer
Albert Schweitzer OM was a German theologian, organist, philosopher, physician, and medical missionary. He was born in Kaysersberg in the province of Alsace-Lorraine, at that time part of the German Empire...
and his humanitarian work in French Equatorial Africa. The image took 5 days to produce, in order to reproduce the tonal range of the scene, which ranges from a bright lamp (relative to the scene) to a dark shadow.
Ansel Adams
Ansel Adams
Ansel Easton Adams was an American photographer and environmentalist, best known for his black-and-white photographs of the American West, especially in Yosemite National Park....
elevated dodging and burning to an art form. Many of his famous prints were manipulated in the darkroom with these two techniques. Adams wrote a comprehensive book on producing prints called The Print, which features dodging and burning prominently, in the context of his Zone System
Zone system
The Zone System is a photographic technique for determining optimal film exposure and development, formulated by Ansel Adams and Fred Archer. Adams described how the Zone System was developed: "I take this opportunity to restate that the Zone System is not an invention of mine; it is a codification...
.
With the advent of color photography, tone mapping in the darkroom was no longer possible, due to the specific timing required during the developing process of color film. Photographers looked to film manufacturers to design new film stocks with improved response over the years, or shot in black and white to use tone-mapping techniques.
1980
The desirability of HDR has been recognized for decades, but its wider usage was, until quite recently, precluded by the limitations imposed by the available computer processing power. Probably the first practical application of HDRI was by the movie industry in late 1980s and, in 1985, Gregory Ward created the RadianceRadiance (software)
Radiance is a suite of tools for performing lighting simulation originally written by Greg Ward. It includes a renderer as well as many other tools for measuring the simulated light levels. It uses ray tracing to perform all lighting calculations, accelerated by the use of an octree data structure...
RGBE image file format
RGBE image format
RGBE is an image format invented by Gregory Ward Larson. It stores pixels as one byte each for RGB values with a one byte shared exponent. Thus it stores four bytes per pixel....
which was the first (and still the most commonly used) HDR imaging file format.
Wyckoff's concept of neighborhood tone mapping was applied to video cameras by a group from the Technion in Israel led by Prof. Y.Y.Zeevi who filed for a patent on this concept in 1988. In 1993 the first commercial medical camera was introduced that performed real time capturing of multiple images with different exposures, and producing an HDR video image, by the same group.
Modern HDR imaging uses a completely different approach, based on making a high dynamic range luminance or light map using only global image operations (across the entire image), and then tone mapping
Tone mapping
Tone mapping is a technique used in image processing and computer graphics to map one set of colors to another in order to approximate the appearance of high dynamic range images in a medium that has a more limited dynamic range...
this result. Global HDR was first introduced in 1993 resulting in a mathematical theory of differently exposed pictures of the same subject matter that was published in 1995 by Steve Mann
Steve Mann
Steven Mann , is a tenured professor at the Department of Electrical and Computer Engineering at the University of Toronto.-Education:...
and Rosalind Picard.
This method was developed to produce a high dynamic range image from a set of photograph
Photograph
A photograph is an image created by light falling on a light-sensitive surface, usually photographic film or an electronic imager such as a CCD or a CMOS chip. Most photographs are created using a camera, which uses a lens to focus the scene's visible wavelengths of light into a reproduction of...
s taken with a range of exposures
Exposure (photography)
In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...
. With the rising popularity of digital camera
Digital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
s and easy-to-use desktop software, the term HDR is now popularly used to refer to this process. This composite technique is different from (and may be of lesser or greater quality than) the production of an image from a single exposure of a sensor that has a native high dynamic range. Tone mapping is also used to display HDR images on devices with a low native dynamic range, such as a computer screen.
1996
The advent of consumer digital cameras produced a new demand for HDR imaging to improve the light response of digital camera sensors, which had a much smaller dynamic range than film. Steve MannSteve Mann
Steven Mann , is a tenured professor at the Department of Electrical and Computer Engineering at the University of Toronto.-Education:...
developed and patented the global-HDR method for producing digital images having extended dynamic range at the MIT Media Laboratory. Mann's method involved a two-step procedure: (1) generate a single floating point image array by global-only image operations (operations that affect all pixels identically, without regard to their local neighborhoods); and then (2) convert this image array, using local neighborhood processing (tone-remapping, etc.), into an HDR image. The image array generated by the first step of Mann's process is called a "lightspace image", "lightspace picture", or "radiance map". Another benefit of global-HDR imaging is that it provides access to the intermediate light or radiance map, which has been used for computer vision, and other image processing operations.
1997
In 1997 this technique of combining several differently exposed images to produce a single HDR image was presented to the public by Paul DebevecPaul Debevec
Paul Debevec is a researcher in computer graphics at the University of Southern California's Institute for Creative Technologies. He is best known for his pioneering work in high dynamic range imaging and image-based modelling and rendering....
.
2010
HDR photography functionality was added to the iPhone 4IPhone 4
The iPhone 4 is a touchscreen slate smartphone developed by Apple Inc. It is the fourth generation iPhone, and successor to the iPhone 3GS. It is particularly marketed for video calling , consumption of media such as books and periodicals, movies, music, and games, and for general web and e-mail...
in iOS version 4.1 on September 8th 2010
2011
HDR photography functionality was added to the Android platform in October of 2011.Video
While custom high-dynamic-range digital video solutions had been developed for industrial manufacturing during the 1980s, it was not until the early 2000s that several scholarly research efforts used consumer-grade sensors and cameras. A few companies such as RED and Arri have been developing digital sensors capable of a higher dynamic range, but have yet to be released or made affordable. With the advent of low cost consumer digital cameras, many amateurs began posting tone-mapped HDR time-lapse videos on the Internet, essentially a sequence of still photographs in quick succession. In 2010 the independent studio Soviet Montage produced an example of HDR video from disparately exposed video streams using a beam splitter and consumer grade HD video cameras. Similar techniques have been described in the academic literature in 2001 and 2007 and 2011.Modern movies have often been filmed with cameras featuring a higher dynamic range
Dynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...
, and legacy
Legacy system
A legacy system is an old method, technology, computer system, or application program that continues to be used, typically because it still functions for the users' needs, even though newer technology or more efficient methods of performing a task are now available...
movies can be upgraded even if manual intervention would be required for some frames (as this happened in the past with black&white films’ upgrade to color). Also, special effects, especially those in which real and synthetic footage are seamlessly mixed, require both HDR shooting and rendering. HDR video is also required in all applications in which capturing temporal aspects of changes in the scene is required with high accuracy. This is in particular important in monitoring of some industrial processes such as welding, predictive driver assistance systems in automotive industry, surveillance systems, to name just a few possible applications. HDR video can be also considered to speed up the image acquisition in all applications, in which a large number of static HDR images are required, as for example in image-based techniques in computer graphics
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....
. Finally, with the spread of TV sets featuring enhanced dynamic range, broadcasting HDR video will be important, but may take a long time to actually occur due to standardization
Standardization
Standardization is the process of developing and implementing technical standards.The goals of standardization can be to help with independence of single suppliers , compatibility, interoperability, safety, repeatability, or quality....
issues. For this particular application, enhancing current LDR video signal to HDR by intelligent TV sets seems to be a more viable near-term solution.
Examples
These are examples of four standard dynamic range images that are combined to produce two resulting tone mapped images.See also
- High dynamic range renderingHigh dynamic range renderingIn 3D computer graphics, high dynamic range rendering , also known as high dynamic range lighting, is the rendering of computer graphics scenes by using lighting calculations done in a larger dynamic range. This allows preservation of details that may be lost due to limiting contrast ratios...
- Wide dynamic rangeWide dynamic rangeThe wide dynamic range function of a camera is intended to provide clear images even under back light circumstances where intensity of illumination can vary excessively, namely when there are both very bright and very dark areas simultaneously in the field of view of the camera.WDR enables the...
- Comparison of graphics file formatsComparison of graphics file formats-General:Ownership of the format and related information.-Technical details:...
- HDRi (data format)HDRi (data format)The HDRi data format is a 64bit or 32bit data format for saving RAW data of HDR scans including infrared data developed by LaserSoft Imaging.- Data format :- Description :...
- RGBE image formatRGBE image formatRGBE is an image format invented by Gregory Ward Larson. It stores pixels as one byte each for RGB values with a one byte shared exponent. Thus it stores four bytes per pixel....
- OpenEXROpenEXROpenEXR is a high dynamic range imaging image file format, released as an open standard along with a set of software tools created by Industrial Light and Magic , released under a free software license similar to the BSD license....
- Logluv TIFFLogluv TIFFLogluv TIFF is an encoding used for storing high dynamic range imaging data inside a TIFF image. It was originally developed by Greg Ward for storing HDR-output of his Radiance-photonmapper in a time, where storage-space was a crucial factor. Its implementation in TIFF also allowed the combination...
- BEF (image format)BEF (image format)BEF is an HDR image format developed by Unified Color. It is supported in HDR PhotoStudio, an advanced HDR imaging application, as well as via an Adobe Photoshop image format plug-in...
- scRGB colorspace