canon digital learning center - hdr photography

Capture More Light: How to Capture High Dynamic Range (HDR) Images with your DSLRThis is the first article of a 3 part series:1. HDR and how to create HDR images2. High speed bracketing method, created by the author (click to read)3. Getting the most out of your HDR images (click to read)

by Uwe Steinmueller (photos by Bettina & UweSteinmueller)

What is this talk about HDR all about?High Dynamic Range (HDR) photography is something you hear digital photography enthusiasts speaking about a lotthese days. Basically, it means combining two or more images — of the exact same scene — taken at differentexposure levels into one finished image. One dark exposure can capture detail in bright areas of the scene, while asecond, lighter exposure can give details in mid-tones and shadows. Combined, the two can give a finished image withfar more overall tonal detail than is sometimes possible to capture with even the finest digital SLRs on the market today. This is especially true in very high-contrast scenes, such as scenics in bright sunlight, and indoor shots taken in thedaytime with bright windows in the scene.As old as photography is the search for the ideal light. Part of this search for light is related to the fact that some scenesjust look better in certain (often warmer) light. But even more it is related to the fact that film and now modern digitalDSLRs can only capture a certain dynamic range.The Dynamic Range (DR) of a DSLR or film is measured by the ratio of the brightest detail in the highlights and thedarkest detail in the shadows. The detail in the highlights is limited by pure highlight clipping and the detail in theshadows is limited in modern DSLRs by the noise level (or film grain).It is common to measure the DR of cameras in the range of Exposure Values (E.V.) spanned, E.V. being oftenexpressed as f-stops (even though photographers usually vary the exposure time rather than the aperture. Some datacan illustrate this:

Examples of Dynamic RangeBlack & White Negative Film 10-11 f-stops, or a DR ratio of about 1,000:1 –

2,000:1Slide Film 6-7 f-stops, or a ratio of about 100:1

07/01/2010 Canon Digital Learning Center

http://www.usa.canon.com/dlc/controll… 1/8

DSLRs (in 2008) 8-10 f-stops, or a ratio of about 250:1 to 1000:1Daylight Scene (with full sun) 12-15 f-stops, or a ratio of 5,000:1 to 50,000:1

(depending on preferred amount of shadow detail) Room Interior, with outside viewfrom window into full daylight At least 17 f-stops, or a ratio greater than 100,000:1

Here is the situation: The scene can have often a larger DR than the camera can capture, and the camera cancapture more DR than we often can print.So why even bother to deal with scenes of a larger DR than we can capture or print? We have the following options:

Control the light (only practical in the studio via flash or lights)Shoot only in low-contrast situationsOvercome the limitation of a single exposure

Exposure MergeOf course all three options are valid. This article concentrates on the last option. How can we overcome the limitationsof our cameras. Because the problem is as old as photography we also had solutions for as long. We capture two ormore separate photographs (from underexposed to overexposed) of the same scene and combine the images into anew photo. The classic solution is called Exposure Blending. Master photographers did this manually in the darkroomwith enlargers, and today the same is done in the digital world in Photoshop™. Seamless manual blending is hard workbecause of the issue of:

Aligning the source imagesMasking the images to get seamless blended results

Most digital photography enthusiasts’ first efforts at combining separate images into one finished HDR image is done inan image-editing software program such as Adobe Photoshop™. Using features such as layers and various maskingtechniques, it’s possible to get excellent results, if the user’s technique from the camera to the computer has beensound.However, today there are quite a few specialized software applications (one that I’ve had excellent results with isPhotomatix Pro) that can are designed primarily for the single task of merging two or more exposures into a singleimage, which is LDR (Low Dynamic Range), but containing the details in highlights and shadows of the exposures fromthe sources images. There are different merging algorithms with different strengths and weaknesses.HDRI (High Dynamic Range Imaging)HDR Imaging is actually something new. We don’t want to confuse you with too much detail, since it is not needed forpractical HDR work. HDR allows you to store image data that capture a nearly infinite tonal range (from the deepest darkareas to open sunlight). The HDR images store image data as 32 bit floating point values in order to encode real valuesof light. Instead of merging different exposures into a single LDR (normal JPEG or 8/16 bit TIFF) image, you can create a HDRimage that can represent all the tonal values in even the most contrasty scenes. Applications like Photoshop™ andPhotomatix Pro can create such HDR files from a series of different exposures. Tone Mapping Methods (Operators)However, there’s a little more to getting good HDR results than just blending two images together. Simply combining twoor more images taken at different exposure levels often isn’t enough to produce an excellent, finished HDR image. Asoftware process called “Tone Mapping” further alters the contrast range, giving a vibrant and deep range of tones that’ssuitable for our computer monitors and printers. High-end image-editing software such as Photoshop™, and many ofthe dedicated HDR software applications such as Photomatix Pro also handle this step. Both applications implementvery different Tone Mapping methods (operators). Right now the Photomatix Pro Details Enhancer method seems to bea popular one. Over the next years other methods will likely appear.



Capturing photos for HDRSince my primary software for combining images into HDR files is Photomatix Pro 3.0, we’ll briefly demonstrate theprocess using this software (this program sells for about $100; free demos are available at www.hdrsoft.com). This isby no means a tutorial on Photomatix but the process in Photomatix is easy to learn. Again, there are also other HDR-dedicated programs you may want to look into; furthermore many users start by combining two or more images withimage-editing software such as Photoshop, and this is perfectly effective as well. For this article it is our intention toshow the principle three-step HDR workflow:1. Capturing bracketed exposures2. Generating the HDR image3. Tone Mapping of the HDR image

Different exposures of the same scene are best created at 2 EV spacing (e.g. -2 EV, 0, +2 EV). All current CanonDSLRs support an AEB (Auto Exposure Bracketing) modus where the camera handles the proper bracketing and alsoallow at least 2 EV steps.

Exposure bracketing in Mark III cameras (left) is done by pressing the Mode & AF Drivebuttons, then making fine adjustments with the Mode Dial. In some other EOS cameras(right), AEB set-up is in the shooting menu.

Custom Function I-5 and I-6 (in the EOS-1D Mark III and EOS-1Ds Mark III) give usersmore control over exposure bracketing.

For normal outdoor scenes, three shots at -2 EV, 0, +2 EV are often sufficient. The camera should be used in Aperturepriority mode. This means the camera handles automatically the different exposures by changing the shutter speed.Movement is the enemy of HDR. Why? Think of combining images where certain parts are at different locations in thedifferent exposures. This is called “Ghosting” because the combined image would show these elements like ghosts.This is why most HDR photographers use a sturdy tripod and all techniques available to minimize camera shake (e.g.



use the “Mirror Up” feature in your camera). Keep this in mind, because in our Part 2 we will show a technique thatworks also freehand — and changes the whole character of shooting HDR images. Slight movements of the cameracan be compensated in the HDR software (even photo series from a tripod are often not perfectly aligned). We demonstrate the HDR workflow on one of our Alcatraz portfolio photos (taken with Canon EOS 1Ds Mark II + CanonEF 24-70mm f/2.8 L USM lens on a sturdy tripod, mirror was up and a cable release used).Here are the three different exposures (original Canon RAW files):

The photos were taken with the following bracketing sequence: 0, -1 2/3, +1 2/3 EV (now, we would use a +/-2 EV exposure spacing).

Processing step #1: Generate HDR imageIn Photoshop CS3, the equivalent function is called “Merge to HDR” (File > Automate > Merge to HDR). As mentionedpreviously, there are alternate methods in image-editing software that are more user-intensive, involving masking andcombining images manually as multiple layers into one finished image.Here’s a quick view of how it’s done in the specialized Photomatix software, which is a program designed specifically forthis purpose. (Other similar software applications will usually offer similar features and steps.) We select our threeexposures in Photomatix and have to select some crucial options:



Generate HDR menu options (inPhotomatix software)

Most of these settings are default values. We nearly always enable the “Align source images” option. There are twodifferent algorithms available. We start most often with the method “By matching features”. Only in some rare cases ifthis fails to work we also try the other option. Once we click ok Photomatix does its job and creates the initial HDRimage.If you see a HDR image for the first time, its excessive contrast comes as a shock:

This high contrast look is actually normal for the initial stages of HDR creation.

Why is this? Remember that HDR images can represent a dynamic range that no normal monitor can display. This iswhat you experience here and that is also why the next Tone Mapping step is essential. If you plan to try different ToneMapping settings or algorithms this would be the time to save the initial HDR image. The images are saved in a file



format that stores the extremely broad 32 bit image data. Popular file formats are: • Radiance: uses a .hdr suffix (our choice)• OpenEXR: uses a .exr suffix (good alternative)

Processing step #2: Tone MappingAlthough Photomatix offers two different Tone Mapping algorithms we nearly always use the Details Enhancer. TheDetails Enhancer performs a tone mapping based on local contrast optimization.

In this step, you can tweak several settings before generating a tonemapped image.

There are quite a few options (sliders) to tweak to get the optimal result. Because this is not a Photomatix tutorial we won’t cover this in detail here. In the end it is not that complicated and you will use similar settings over and over again. Ifyou hit Process, Photomatix generates a tonemapped 16-bit image. Now, the contrast range will seem much moreappropriate for the scene and its lighting.



The tonemapped result will look much closer to the original scene and lighting -- givingyou an excellent base for further editing in Photoshop or similar software.

In our work the tonemapped image (saved as 16-bit TIFF) is never the final result. We always use Photoshop™ for finalretouching and sharpening. Even though most final, tonemapped HDR images are color images, in this particular case,we opted for a B&W version:

Here is our final HDR image (after a black & white conversion).



Summary of Part 1Capturing multiple images with your camera and combining them into finished tonemapped HDR images is quite simpletoday. Getting the right artistic results will as always take some time practice and experimentation. In Part 2 we coverour “High Speed Bracketing” technique which builds on the technique you learned in Part 1.We conducted some workshops on HDR called “Capture more Light”. All our students found that working with HDR isfun because it adds a new tool to your creative process. Final note of cautionWe mentioned it in this article: Movement is the enemy of HDR. This means that you have to watch for everything thatmoves. Here is a list of common ghosting* candidates:

PeopleCars, bicycles, and other vehiclesLarger animals (dogs, cats,...)Small animals (birds, butterflies,..)CloudsWaterFlagsTrees and plants in wind (means nearly always ☺)

* In Part 3 we will talk a bit more about ghosting. Uwe Steinmueller started practicing photography in Germany thirty-five years ago. Still an international artist, Uwe is now based inCalifornia and continues to collaborate with his wife and long-time creative partner, Bettina (sharing a joint copyright to their images).Working completely in digital photography since 2000, his current work focuses on digital work flow, raw file processing and the printingprocess. He has written, and continues to publish, several electronic and printed books in these areas. Uwe also acts the editor-in-chief of the independent online magazine Digital Outback Photo, a popular resource for outdoor digital fine art photography. You canlearn more about him and his work at www.outbackphoto.com



Capture More Light: HDR and High Speed BracketingThis is the second article of a 3 part series:

1. HDR (High Dynamic Range) and how to create HDR images (click to read)2. High speed bracketing method3. Getting the most out of your HDR images (click to read)

Written by Uwe Steinmueller (photos by Bettina & Uwe Steinmueller)

Many of today’s digital photography enthusiasts think of shooting different High Dynamic Range images of the same sceneas a tripod-only exercise. Thus, many dismiss HDR photography as something suitable only for totally static subjects, shotin a slow and methodical fashion. However, with the shooting speed of today’s cameras, this doesn’t have to be the case.This article demonstrates how you can use this speed to shot HDR images in circumstances you may never haveconsidered before.

Improving the dynamic range that our digital cameras can capture is for us as important as getting higher resolution (moreMegapixels). We covered in part 1 of this series how bracketed images can help to capture more dynamic range using HDRtechniques.

The enemy of merging images is any sort of movement (moving objects or moving cameras). That is why exposurebracketing is most often only applied to static objects and the camera is mounted to a sturdy tripod. This of course imposeslimitations what we can shoot using HDR.

If in theory these multiple exposures could be captured instantly both issues -- Moving objects, and camera movement --would be no problems at all. We may actually see in the future cameras that could implement this kind of strategy: capturemultiple exposures, create HDR internally and still freeze even faster moving objects.

Click here to learn about the bracketing functions of Canon's Mark III and Mark II series cameras.



Speed MattersWhen we first used a Canon EOS-1D Mark III camera, we did not think to use its speed (it can capture 10 fps) for ournormal work. Its primary target audience is sports, newspaper/magazine, and also wildlife photographers. In general wephotograph more static nature or urban landscapes. Like many digital shooters, we initially thought that fast bursts ofimages in general do not matter for us. However, once we got used to the 1D Mark III we started experimenting with what wecall “High Speed HDR”. What does this mean? The camera is set to the highest burst rate (10 fps) and we capturebracketed shots at this speed. This means a 3 shot (e.g. -1 1/3, 0, +1 1/3 EV) bracketed sequence is shot in less than half asecond (with hand-held shots your shutter speed is mostly faster than 1/50 sec). Why does it make a difference?Everything that does not move much in 1⁄3 second is frozen in all three exposures. It limits the camera movement and alsocaptures all slow moving objects reasonable sharp. And perhaps most important: it opens the door to shooting HDR imageshand-held.

Important Note: We now use the same technique successfully with many other cameras as well (Canon EOS 40D, EOS-1Ds Mark III, Rebel XTi). Of course the speed of the 1D Mark III is not matched by these other cameras but it still works quitewell for us. With the 1D Mark III it is even very easy to capture 5 shot bracketed sequences like -2, -1, 0, +1, +2 EV.

We used this technique now for over a year and at least 5,000 photos (these are about 15,000 exposures at 2, 3 or 5 shotbrackets). It changed our photographic style. For us it is not only a photo technique but also a photographic philosophy.

Good and bad light?Photographers talk a lot about “good” and “bad” light. Actually, they’re usually referring to the quality and contrast of light, notwhether it’s bright or dim. Often, it is bad because normal film or digital cameras cannot capture the dynamic range in thescene. Using HDR techniques (multiple exposures and tone mapping) you can capture quite a bit more dynamic range.However, freezing movements is essential. We are using “High Speed HDR” now in many light situations that we calledpreviously “bad” light and get very pleasing results.

The sample we later present in this article was shot at strong sunlight in Bryce Canyon (11am ☺).

Notes on camera techniqueWe exclusively use image-stabilized zooms (most of the time in the 24 to 200mm range), and shoot handheld. The ISOrange is set to a value that allows us to keep even the longest exposure in our bracket sharp if shot handheld (but alsotaking the image stabilization into account).

Exposure Mix & Match: PhilosophyWe add this more philosophical section because some of our readers may think this is all just technical mumbo jumbo andthey rather take photographs. Of course they have a point here and many different ways lead to Rome. You have to work theway that fits best for you. There is no one universally best practice.

Photography falls into two principal activities:Framing and ExposurePost-processing

We think both parts are equally important although we spend way more time processing than taking pictures.

Framing and Exposure Without the right composition and an at least decent exposure there is hardly a chance to get a good print. The ideal wouldbe to concentrate only on creative aspects like composition and leave the rest to the camera. But even with today'ssophisticated cameras there is a lot to consider:

f-stop: Depth of field but also diffraction limits (beyond a certain point, as lens apertures get smaller, sharpnessactually decreases)Shutter speed: Consider moving objects and camera shakeISO: Allows higher shutter speeds at the expense of more noiseTripod vs. Hand-held: This is a whole can of worms and a very personal decision. Of course it even more depends onthe situation. Night shots are not often done freehand (except at very high ISO values). Freehand or hand-held allowsmore flexibility while the tripod is a strong aid to get the best framingExposure: Mostly about not clipping (over-exposing) the highlights, while avoiding underexposures to keep the shadownoise in check



Capturing bracketed shots makes exposure much easier. We can almost always be confident in capturing one or moreimages with sufficient sharpness and without blown-out highlights. This gives us a chance to concentrate on the framingaspect.

About the only downside of this approach is we capture more images, and they have to be stored someplace (bigger CFcards and disks). Otherwise bracketing was and is always very useful.

Post-processingShooting brackets makes post-processing easier and more complex at the same time.

Easier, because:Having 3 or more exposures available allows finding the best possible exposure of the bracket. With only a singleexposure you have to live with it and fix things that might gone bad (e.g. blown highlights — hard to fix if at all).More Complex, because:Having options is always nice but also makes life more complicated. If you ignore HDR all is quite simple. But if youwant to explore these options, this will clearly cost more time and work.

With bracketing, you capture more images that allow you to revisit some of these issues later (e.g. HDR, lower noise, ...). Ifyou capture only single shots this can be just fine but it also limits your options.

Exposure Mix & Match: Technique

We created a few diagrams that discuss the preparation for you shooting and the evaluation of the resultingshots:

Control Camera Movement

There are two principle different situations:Tripod mountedFreehand

Tripod Mounted(You need to use all techniques available to stabilize the camera/lens on the tripod.)

Use mirror lockup (even better, use live preview available on some new DSLRs)Let the tripod rest between shots (to avoid vibrations from previous exposures)It is better to use manual focus as the camera AF may shift during bracketed shots

Freehand (hand-held)Use the fastest shutter speed you can afford (this is a balance of ISO & noise vs. shutter speed)Use image-stabilized lenses, whenever possible. Don't assume this does miracles. We try to be very conservativehow much the IS buys us (but 1-2 f-stops is already a lot). Some more recently-introduced Image Stabilized lensesoffer even higher performance, allowing safe hand-holding at speeds up to 3 or 4 stops slower than otherwisepossible.You may also use a monopod for extra support (light yet sturdy)

Consider Moving Objects



Fast moving objects: HDR does not really buy you anything if there are faster moving objects. Fast is in relation to thetime it takes to take all bracketed shots. From tripod all movements can be considered too fast. With High SpeedHDR many movements can still be captured without too much blur. Not all blur is actually a problem. This is then anartistic decisionSlow moving objects often don't show with High Speed HDRSome movements may not bother you: Clouds, distant people

Essential Camera Settings

Highlight Tone Priority: This is a unique new feature on select EOS models, such as the EOS-1D Mark III, EOS-1DsMark III, and EOS Rebel XSi. It allows you to record some detail in bright highlights, in slightly overexposed shots.Remember our technique is also about getting the single best exposure from the bracketed shotsEnable camera auto bracketingFor High Speed HDR we need about 3-10 frames per second speed (the higher the fps the better)

Controlling the Bracketing

Number of shots per bracket: We use mainly 2, 3 or 5 for our High Speed HDR technique. Seven or more shots arereserved for pure tripod based bracketing. (Please note: Canon’s EOS-1D and EOS-1Ds models allow choosing thenumber of bracketed frames in a sequence, from 2 through 7. All other EOS models [as of July, 2008] are limited to 3shots whenever auto bracketing is activated)EV spacing depends on the dynamic range we want to capture. We most of the time use about 1-1/3 EV (1.3 stops)but in some situations 2EV is better. How did we come up with 1-1/3 EV? In this case the best shot in the bracket canbe only about 2/3 EV off an optimal exposure because Highlight Tone Priority allows us easily to recover at least2/3EV overexposureISO and f-stop should be constant for all shots in the bracket. The only variable should be the shutter speed. Thismeans shoot in Aperture-priority exposure mode

Evaluating the Bracketed Shots



We have to consider two goals:Capture a good single exposure as part of the bracketAllow as often as possible to merge images for HDRIn case you have visible object movements during the full cycle taking all bracketed shots you have two choices:Accept the resulting artifacts when merging the exposuresUse on a single best frame from the bracket

A) Overexposed shotThis is often the least usable shot working freehand. Why? Because it uses the longest exposure time and so the imagecan easily get blurred. Always watch the shutter speed for this shot.

If the clipped highlights in this shot can be properly recovered through software intervention (Canon's DPP, Adobe CameraRaw, and LightZone all offer effective recovery tools) and the image is not blurred, you actually have all the information youneed.

B) Middle ExposureIn most of our cases (using the camera’s Aperture Priority “Av” mode) we can recover this shot properly using highlightrecovery to some extent. If the image does not show motion blur we have a good single shot photo. If you want to open upshadows a lot, this is possible, but you may increase the digital noise. In this case, we try to reduce the noise in theshadows by using commercial noise removal software.

C) Underexposed photoIt is often not good if you need to use only the underexposed shot because it shows the strongest noise — especially onceyou try to lighten it using image-editing software. On the other hand, it can still get you good results if you stay at lower ISOvalues or accept some noise in your image.

D) HDR MergingIf there are hardly any object movements (remember, for minor camera movements, the software alignment algorithms willtake care of this) you can merge some exposures.

All three exposures if all three shots don't show motion blur and are in focusOnly two exposures if one of them shows motion blur or is out of focus (most likely the overexposed shot)

Sample Mix & Match



-2 EV -1 EV 0. EV

+1 EV +2 EV

These five exposures were taken with a Canon EOS-1D Mark III at -2, -1, 0. +1, +2 EV. The most overexposed shot (fifthphoto, +2 EV) also has the longest exposure time, and we often discard it. In this case we only used three shots: The firstphoto (maximum underexposure, with most highlight detail), the third photo (0. EV, middle exposure), and the fourth photo(slightly overexposed, and low noise in the shadows).

After merging to HDR and Tonemapping (Details Enhancer) we get this result:

Resultant HDR image, tonemapped in Photomatix

We actually nearly always use a two-step process (described in Part 1 of this series):1. Tonemapping in Photomatix software2. Final tuning in Photoshop

Here is the final resulting photo. In this case the tuning was really minor. This is not always the case.



The final image, after minor tuning in Photoshop

ConclusionHigh Speed Bracketing/HDR is a new and powerful technique. Being able to capture good photos hand-held and at normalsunlight opens incredible new possibilities. For photographers whose style is to work quickly, without a tripod, it makes HDRshooting a practical option. Besides more space for images and more imaging work we don’t see a lot of disadvantages. Ifsome of the objects move too much we can pick the best single exposure.

We also experiment with different bracketing sequences:-1, 0 EV: saves space (possible only with EOS-1D/ EOS-1Ds models)-1, 0, +1 EV: would allow getting a good optimal single exposure that cannot be more than 1⁄2 f-stop off-2, 0, +2 EV: if you want to captures a larger dynamic range. The +2 EV exposure may often require the use of thetripod though-2, -1, 0, +1, +2 EV with very fast cameras like the 1D Mark III-1 1/3, -2/3, 0, +2/3, +1 1/3 EV optimal fine exposure spacing (use only with very fast cameras)

All the following elements are very important:Fast frame rateHighlight Tone Priority (a Custom Function on select EOS models)Merging to HDRTonemapping

We honestly can say that we got a lot of fun using this technique. Only our disks complain about the data volume weproduce. We have more data because of the bracketing but also a higher keeper rate.

Uwe Steinmueller started practicing photography in Germany thirty-five years ago. Still an international artist, Uwe is now based in California andcontinues to collaborate with his wife and long-time creative partner, Bettina (sharing a joint copyright to their images). Working completely in digitalphotography since 2000, his current work focuses on digital workflow, raw file processing and the printing process. He has written, and continues topub lish, several electronic and printed books in these areas. Uwe also acts the editor-in-chief of the independent online magaz ine Digital OutbackPhoto, a popular resource for outdoor digital fine art photography. You can learn more about him and his work at www.outbackphoto.com

Back to beginning of tip



Bracketing with EOS Mark III and Mark II series cameras:

EOS-1D Mark III, EOS-1Ds Mark III:Use Custom Function I-6 (Number of bracketed shots). Default is 3-shot bracketed sequence; choices are 2, 5, or 7bracketed shots. If two shots are chosen, you determine whether it's normal exposure plus over-exposure, or normalplus an under-exposed frame via C.Fn I-5-1 or I-5-2.

Original EOS-1D, EOS-1Ds, and all Mark II series:Install Personal Function 8 into camera (connect FireWire cable from camera to computer, activate EOS Utility orEOS Viewer Utility software, go to Camera Settings > Personal Functions, and upload P.Fn 8 into camera afterselecting 2, 5, or 7 bracketed shots as an option). Then, once installed, P.Fn 08 can be turned on or off in camera'smenu. If user selects 2-shot bracket using P.Fn 08, Custom Function 09-0 or 09-1 provides a normal and under-exposed frame; C.Fn 09-2 or 09-3 generates a normal and over-exposed bracketed 2-frame sequence.



Capture More Light: Getting the Most Out of Your HDR ImagesThis is the final article of a 3 part series:

1. HDR (High Dynamic Range) and how to create HDR images (click to read)2. High speed bracketing method (click to read)3. Getting the most out of your HDR images

Written by Uwe Steinmueller (photos by Bettina & Uwe Steinmueller)

It sounds so easy to combine images -- and, technically, it really is. This article covers some of the major challengestowards getting excellent HDR photos.

We cover the following aspects:Camera Settings (Exposure)AlignmentGhostingChromatic Aberrations (CA)

As mentioned in the previous articles, the main concern for HDR photography has to be all kinds of movement. This meansthat most of the challenges are related to dealing with different kinds of movement.

Camera SettingsFor a proper exposure, these factors should be constant for all exposures in the series:

F-stop (shutter speed with vary for each exposure; we suggest aperture-priority mode)Focus (sometimes using manual focus can be a plus)White balance (can also be changed later in post processing; we use Auto WB and then change the WB later whenprocessing the RAW images)Movement (the camera should not move or shake -- use Live View, if available, to lock the mirror up when shootingfrom a tripod)ISO (should not change)

The only parameter that should change is the shutter speed.



AlignmentPerfect alignment is key to a good HDR image generation. If the images are not perfectly aligned, it is like blurring yourphotos. You don’t want to use a high quality digital SLR and then throw away the resolution by poor alignment. Today’s HDRsoftware is very effective to correct the alignment.

Here is a sample with and without good alignment.

Roll mouse over image to see the detail with, and without, good alignment

Photomatix does a good job aligning the images -- but in some cases we use Adobe Photoshop CS3 to align our images.Because it is not common knowledge how to perform the alignment in CS3, we cover it here.

Image Alignment in Photoshop CS3Photoshop CS3 does a very good job aligning images. Here is how to align images for the purpose of later HDR generationin Photomatix, or other HDR software.



Start by gathering your bracketed images

To align these three images you use the CS3 function File -> Scripts -> Load Files Into Stack. The following dialog showsup (after you selected your source images):

Make sure to leave all option boxes UNchecked, as pictured here.

After clicking OK, CS3 will load the three files as three layers in a single file. If you've shot RAW images, opening them inPhotoshop automatically converts the RAW files using Adobe Camera Raw (note that the layers retain the .CR2 extension,but are no longer RAW files). We then select all three layers:

You will see your bracketed images layered in one file.

Now you use the CS3 function Edit -> Auto-Align Layers and get this Auto-Align Layersdialog window.

Use the Auto option and click OK. CS3 will then align the layers.

This is not just a simple shift operation. CS3 can perform:Shifts (up/down or right/left)Rotations (if the camera gets tilted)Morphing to stretch (if the camera gets closer or further away)

The result is quite remarkable. Once the layers are aligned you should inspect the result(making layers visible/invisible) and crop the image to the parts that are present in all yourbracketed photos.



Here is the key part: We want to create new TIFF files that represent the layers after alignment. Fortunately CS3 has a neatlittle function: File -> Scripts -> Export Layers to Files

Save your newly aligned images as a TIFF file.

We only mention the important parameters.Destination: Folder for the new filesFile Type: TIFF (you don’t want to lose quality using JPEG; The bit depth is the same as the source images, and bestis 16 bit)Include ICC Profile: Always checked

That is all there is to it. You now have a new TIFF files that you can use to generate HDR images. If you then usePhotomatix, do not check “Align images” because they are already perfectly aligned. There is no general rule whenPhotoshop may align more perfectly than Photomatix. That decision has to be made on an image-by-image basis (thedifferences can be very subtle, but we aim for optimal resolution).

GhostingWhile misalignment is related to (minor) camera movements, ghosting is caused by moving objects in the scene.

Here some common causes:Moving branches and leavesFlying birdsFlagsPeople and larger animalsCarsCloudsWater

We are not too enthusiastic about the tools that can help to remove ghosting. If you want a crisp and sharp image, ghostingmay spoil your party. One of the only truly effective and preventative shooting techniques is to take many, many pictures ofthe same scene -- then, it may be possible to remove elements like people, cars and animals because (if you're lucky) oneof the frames may not show the object.

Let’s have a closer look at some of the causes (and suggested solutions) to ghosting:

Moving



Movingbranches

andleaves

Never underestimate the effect of even a gentle breeze. You will find some nasty artifacts in yourpictures. The ghosting feature in Photomatix may reduce the effect a bit. In some cases it maysave your day (especially from B&W photos).

Flyingbirds If the birds are just in the sky try to use spot healing in Photoshop CS3 to clean them up.

Flags The only option we see is to clone the flag out of the picture. Can be tricky.

Peopleand larger

animalsIf the ghostly appearance of people fits into the picture (e.g. in the distance) all is fine. Otherwisethis maybe a lost cause.

Cars If you have a replacement shot fine. Otherwise forget about it.

Clouds Clouds are often no problem at all if they do not interfere with other elements in the photo.

Water Water can work if it is slow moving. Surf often looks odd.

Chromatic AbarrationsOften, you may see artifacts in your images, like these below -- this is a result of chromatic aberrations (sometimes calledcolor fringing):

Chromatic aberrations may be seen, even with top-rated lenses.

What is chromatic aberration (CA)? Most lenses are not perfect, and can sometimes focus the red, green and bluechannels on different planes (relative to the sensor). This can produce green/purple fringes at higher contrast edges. Theeffect is stronger towards the corners than in the center. Even top rated zoom and wide-angle prime lenses can show thisartifact, especially at higher contrast edges. Remember, we use HDR to cope with capturing higher contrast scenes; thismeans we have to deal with chromatic aberration. Besides misalignment, we find CA one of the major show stoppers forour HDR photography. Fortunately, CA can quite easily be fixed.



A tone mapped, or blended, image shows often stronger chromatic aberrations than the source images (cumulative effect).Careful inspection of the source images is needed to reveal CA.

Fortunately, modern RAW converters like Canon Digital Photo Professional (DPP) can help to fix chromatic aberrations.Here is the simple method to correct CA in DPP (you’ll need to do this with each RAW file in the HDR sequence): Open theLens Aberration Correction function, and just checking the Chromatic Aberration box does the trick:

With one click, DPP can remove chromatic aberrations.

Be sure you correct all the images in your bracketed series (please note that DPP software is only compatible with RAWimages from Canon digital SLRs).

Here is the before and after, using this workflow to remove unwanted CA.

Summary



For most of the challenges the HDR photographer faces, there are good solutions to fix them:AlignmentExposureChromatic Aberrations

Ghosting, unfortunately, is not that easy to fix. You are much better off to carefully examine the scene before you shoot, andavoid moving elements in the first place whenever possible.

Uwe Steinmueller started practicing photography in Germany thirty-five years ago. Still an international artist, Uwe is now based in California andcontinues to collaborate with his wife and long-time creative partner, Bettina (sharing a joint copyright to their images). Working completely in digitalphotography since 2000, his current work focuses on digital workflow, raw file processing and the printing process. He has written, and continues topub lish, several electronic and printed books in these areas. Uwe also acts the editor-in-chief of the independent online magaz ine Digital OutbackPhoto, a popular resource for outdoor digital fine art photography. You can learn more about him and his work at www.outbackphoto.com



canon digital learning center - hdr photography

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