technology high dynamic range imagingstatic.hasselblad.com/2015/02/masteroflightandshadow.pdf ·...

TECHNOLOGY HIGH DYNAMIC RANGE IMAGING

BY MICHAEL J. HUSSMANNPHOTOS: CLAUS-PETER DUDEK

44 1/2006

MASTER OF LIGHT AND SHADOW

21503_E_44_49_Tech_HDRIneu.QXD 05.09.2006 11:32 Uhr Seite 44

Photography means “to write withlight“, but photographic techniquescan only register a small percentageof light values between the brightestdaylight and the darkest night. Printfilm can reproduce a contrast rangeof approximately 10 aperture stops,i.e. a relationship of about 1 to 1000;slide film has an even lower dynamicrange. In this matter, the image con-verters of digital cameras are not, as

often suggested, handicapped; a digi-tal camera can reproduce abouttwelve f/stops, thus a relationship ofapproximately 1 to 4000. This dyna-mic range is sufficient for most appli-cations, but even the most everydaysubject can overwhelm a digital oranalog camera with the richness ofits contrasts.

This includes the view lookingfrom inside a room to the outside, as

well as the view from outside into thecomparatively dark interior, subjectsin which the sun or artificial lightsources are visible in the picture, or simply subjects that are partly inthe dark, partly in bright sunlight.Whenever a subject is not illumi-nated homogeneously and there arecontrasting light conditions in differ-ent parts of the picture, the contrastcan easily surpass the camera’s dyna-

mic range; a tonal spectrum fromone to several million is not a rarething. Photographing such subjectsis always based on a compromise – anexposure on the lights leads to anoverall underexposed picture, whilean exposure on the darks results inblown-out highlights.

Our eye can also only perceive asmall percentage of the tonal rangeat once and is limited in a similar wayto the image converter of a camera –but there is one element where oureyes function differently, namelythat they only focus on a small angle,scanning the environment to regis-ter the overall scenery. While oureyes leap from detail to detail, theyadapt to the varying light; from theindividual impressions registered

This Lexus was never at the beach

of St. Peter Ording, nor was it

ever in photographer Claus-Peter

Dudek’s studio. HDRI panorama

photography and 3D modeling merge

virtuality with reality

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High Dynamic Range Imaging (HDRI) is designed to show all the tonalvalues in a picture, from the brightest lights to the darkest shadows. The potential that HDRI, in combination with panorama photographyand 3D modeling, opens up for a new kind of photography is shown bythe work of Claus-Peter Dudek for his clients in the automobile industry.


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this way, our brain assembles a com-plete picture and reproduces anexceptionally high contrast range.The human eye thus knows neitherover- nor underexposure, nor limitsto the differentiable tonal spectrum.

CREATING HDR EXPOSURES

In order to reproduce a similarlyhigh dynamic range with photo-graphic means, you would have to expose the same subject with dif-fering exposure settings, thussimulating the dynamic adaptationof the eye. Every exposure registers adifferent part of the tonal spectrum –in a fast one, the detail in the lights ismaintained, while in a longer one

the shadow will be well differen-tiated. The tonal values of theindividual frames in the exposure series overlap, and when you mergethem into an HDR picture in animaging program they can cover anygiven tonal range – the more variedthe exposures, the larger the desiredcontrast.

Regardless of how high the dyna-mic range can get, printing pro-cedures cover only five aperturestops and even the presentation onthe computer screen cannot measureup to the contrast range of the actualdata. In order to reproduce an HDRimage truthfully, its tonal value hasto be compressed to the respectivefew f/stops that can be differentiatedin print or on the computer monitor.

A mere compression of the contrastswould result in flat images – if thebrightest lights and the darkestblacks were separated by only a fewf/stops, the reproduction of tonal va-lues would be limited to minimalbrightness differences across most ofthe image.

For this reason you would empha-size the most important part of thetonal spectrum at the cost of the re-maining tonal values, whereby youcan compress individual elements ofthe picture separately from one an-other in an attempt to reproduce, tosome extent, the real contrast rangein spite of the limitations of printmediums. The quality of an HDRimage largely depends upon this laststep. Frequently, a photographer

goes for a spectacular effect but mis-ses the actual point of HDRItechnology, which is to up the pho-tographic tonal reproduction to thelevel of the ability of the human eye.

HDR EXPOSURES INTHE PHOTOGRAPHYOF AUTOMOBILES

The new photographic potentialthat arises with HDRI becomes clearwhen we look at the work of Claus-Peter Dudek, photographer in Ham-burg , as he is hired by car companiesto fuse HDRI, panorama photogra-phy and 3D modeling into a flexibletechnique for product visualization.One of Dudek’s specialties is in pho-tographing new cars in attractive

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The shiny paintjob of the virtual

Lexus in the foreground reflects

the scenery behind the viewer.

Even under strong magnification

you would not be able to tell the

3D model apart from the real cars

parked in the back right


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settings – commissions that can onlybe realized by surmounting a num-ber of challenges. Transportingprototypes to a photo shoot on loca-tion is difficult, often impossible.The only alternative that generallyremains is to photograph the vehiclein the studio and later superimpose itonto an outdoor image. The lightingin the studio thus has to be adaptedto the light conditions of the loca-tion, and, in order to accentuatecritical details effectively, several dif-ferently illuminated exposures mustbe merged before the result can bemounted into the scenic shot.

After that, convincing shadowsand reflections have to be retouchedinto the picture – a particularly so-phisticated task, because the effect ofthe paint finish relies heavily uponthis. If the client desires last minutechanges – be it a different configura-tion, an alternate paint finish or afinal change to design details – thenthe work has to start all over again.This is how Dudek used to work. To-day, a 3D model of the car frequentlyreplaces the elaborate studio shoot.These high-detail 3D models areavailable as a byproduct of industrialproduction and, if need be, only haveto be rendered into a photo-realisticformat. In the ideal scenario the model can be used for the exteriorand interior views, as well as forother details in between – allowingyou, for instance, to present the carwith an open door, complete withlock, handle and window button.

THE PHOTOGRAPHICTECHNIQUE

Embedding a 3D render in a pho-tographed environment obviouslyrequires more than conventionalphotographic means – at least if youwant credibility. The outdoor shot relied upon a specialized camera, aSpheroCam HDR by Spheron VR AGin Waldfischbach-Burgalben, Ger-many. By rotating its CCD scanlinethe SpheroCam HDR exposes a 360-degree panorama, taking only a fewminutes even at the highest qualitysetting. With a fisheye lens mountedvertically, the camera registers anangle of 180 degrees vertical and canthereby create a complete sphericalpanorama. Thanks to automatic ex-posure sequences, the HDR versionof the SpheroCam can extend the dy-namic range to 26 f/stops, making ita precise measuring tool for all lightconditions, from direct sunlight toabysmal blackness. Using a secondpanorama taken from a slightly alter-ed angle, you can, per triangulation,calculate the distance between any

from the picture; then it is retouchedmanually, whereby the camera tri-pod and its shadow are eliminated.

REALITY MEETS VIRTUALITY

The SpheroCam HDR provides theconditions for the photo-realisticrendering of the car, which is placedvirtually in the center of the panora-ma – in other words, precisely wherethe camera had been standing, so

The photographer chooses the

composition in which the car is

to be embedded from the HDR

panorama taken on the beach in

St. Peter Ording

Adapting the image to the 3D

model requires a fair amount of

retouching; the existing tire

marks have to be adapted to the

wheelbase of the Lexus

From the known material

characteristics of the car body

the 3D software can compute

a realistic view of the model car;

the reflections show the real

scenery including elements that

are not shown in the composition

but which were captured in the

spherical panorama

The 3D software can

calculate from the brightness

levels captured in the HDR

panorama how the shadow is

cast by the car

that you don’t have to retouch thatarea; but smaller deviations from thisposition are also possible. The pan-orama not only fully reproduces theenvironment, allowing you to designrealistic reflections and the like, it al-so registers the intensity of the lightthat falls onto the car from everyangle. Unlike conventional cameras,which merely approach an authenticreproduction of tonal values, theSpheroCam HDR can measure alllight values from the deepest shadow

up to a 67.108.864-times brightersource. From this data, the Spheronsoftware can calculate a light field tohelp Maya, a 3D modeling software,reproduce natural-looking light andshadow effects. And not only do thereflections look natural, they are na-tural – they are reflections that wereactually there, behind the viewer, asthe spherical panorama capturedthese, as well. The 3D applicationcan now generate any given view,showing the virtual car parked in

given picture detail and the cameraby marking the respective positionsin both panoramas. In spite of thepanorama camera being quite fast,the lighting may change during theexposure; clouds might move beforethe sun. In such cases the brightnessdifferences are either corrected inpostproduction or the exposure se-quence is simply repeated. Afterexposure, the control software of theSpheroCam removes the reproduc-tion errors caused by the fisheye lens

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authentic scenery – you can view itfrom all angles, including the bird’seye view, the interior view and theview out of the car. An HDR panora-ma and a 3D model enable you togenerate multifold perspectives, andyou can easily present an alternative-ly configured or painted model indifferent environments. Last minutechanges, as ordered by the client,thus represent no major challenges.

Claus-Peter Dudek not only usesthis technology to produce individu-al shots – posters and the like – forprint campaigns, but also for moviesand interactive online presentations:virtual camera rides around the car,navigable panoramas, and “con-figurators“ for the prospective carpurchaser, allowing him, with theclick of the mouse, to switch betweenthe countless car interior and exteri-or configurations, shown perfectlyrendered in a genuine backdrop.

THE IMAGINATIVE EYE

This kind of photography has little incommon with classic photography.Today even photographs taken theconventional way are often compos-ed of several, differently exposedpartial views. This blurs the bordersbetween traditional technology anda hybrid version of photography andother procedures. Yet, the specificphotographic character of this mo-dus operandi is maintained, becausethe photographer still has many ofthe same tasks. The ostensible photois indeed a computer- generated viewof a chiefly virtual reality, but thephotographer can and must accesshis studio knowledge. This enablesthe photographer to consciously addlight sources with predefined charac-teristics to the virtual scene. He canplace brighteners that virtually re-flect the light that was presentduring the shoot; and the panoramaexposure already challenges his ima-ginative eye. As the photographerexposes the background of a subjectthat, when starting out, only existsin his head, he has to anticipate po-tential problems and conflicts thatmay arise during the montage.

3D modeling is not a universal so-lution to all photographic problems.Rather, it is limited to subjects fromindustrial production, which are fair-ly easy to model and already exist as reference for the real-life product.What’s more, as realistic as the gene-rated images then may be, when itcomes to precisely reproducing thetiniest details of form and fabric, vir-tual technology still has its limits, atwhich point Claus-Peter Dudek sim-ply grabs his Hasselblad H2D-39.

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HDRI – AT A GLANCE

2 THE CAR MODEL

1 HOW AN HDR IMAGE IS MADE

3 THE SPHEROCAM HDR

A digital camera reproduces a

limited dynamic range; but when

a series is produced with varied

exposure settings, every exposure

captures a different part of the

overall tonal spectrum. Combining

them into a sandwich, the dynamic

range of the resultant picture can

be as big as you want it

The motor-controlled panorama camera rotates around its own

axis while registering 180 degrees vertical with a vertically mounted

fisheye lens. By means of automatic exposure sequences the

camera can differentiate a contrast range of up to 26 aperture stops

Post-manipulating the panorama image: once the

exposure has been controlled in this histogram (right)

the panorama picture has to be equalized (above)

Industrial production often uses

highly detailed three-dimensional

models containing components

that are not even visible to the

viewer, such as the window button

and the door lock


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