2012-12-16

HDR Technique for Stanley Forest Burn Photo

How To article showing HDR techniques.

The Stanley Basin, near Idaho's famed Sawtooth Mountains, is a forest of mostly lodge pole pines with little undergrowth.  In the summer of 2012, droughts, beetles and lightning strikes caused many of the stands to burn and tens of thousands of acres were lost.  This is an HDR photo taken a month after the fire and this article discusses how the photo was made.

HDR is the technique that blends multiple exposures of the same scene into one photograph.  When using HDR (High Dynamic Range) you can choose to be subtle, dramatic or unbelievable.  My goal was to be more dramatic. 

Final Results:

Stanley Forest Burn, October 2012 - Click for larger view


The Photograph:

The photo was taken mid-afternoon on a heavily overcast, rainy day, using a grey-card for the main exposure, and white-balanced.  Below is the scene, as it appeared "correctly exposed" at EV +0 - no compensation and no editing:


HDR Exposures:

An HDR photograph takes three or more frames, bracketed at various exposure compensations, then with software, all are blended into a final image.  Traditionally, you would take one shot at -1 stop under-exposure, a second shot at the correct exposure, and a third at +1 stop over-exposure.  The HDR process combines all three into one picture.

With this, you can pull in shadow and highlights that would be lost to a single exposure. In other words, you do not have to sacrifice shadow detail to capture highlights.  The technique can also enhance, and some would say exaggerate, contrasts and colors.


For this photo, I took a sequence of 5 exposures, from -2 stops to +2 stops.  All five were combined to build the image above, plus other adjustments, such as saturation and hue, offered during the HDR process:
Bracketing Sequence + / - 2 EV - Click for larger view

The exposures can be taken automatically by the camera, using a feature often called auto-bracketing -- letting the camera pick each of the exposure settings.  But my Nikon D5100 is limited with only a three-frame sequence, typically -1 stop EV, 0, +1 stop EV, and my software can accept more.  Because of this, I bracket manually using Exposure Compensation. Having more frames, for example, -2 EV, -1 EV, 0, +1 EV, +2 EV, produces more nuanced results.  It is unfortunate that the Nikon does not have a variable setting for the number of frames. 

Although many newer cameras can perform HDR exposures in-camera, there is little control over the results and because of that, I never use a camera's built-in HDR.  If you decide to use the internal HDR, be aware it does the bracketing for you and, in the case of the Nikon, only three frames are used.


Follow these exposure steps:

1. Place the camera on a tripod and set the camera to Aperture-preferred automatic (or manual).  Do not use Program or Shutter-preferred as you want the depth-of-field to remain constant during all five exposures; you do not want a program-mode shifting the f-stop.

2.  I recommend setting White Balance.

3.  I highly recommend shooting in a RAW format, rather than JPG.

4.  Meter the scene with no exposure compensation (EV +0); I typically use a grey card but the camera's default meter reading is probably adequate.  This is what I call the base exposure.  Do not bother taking a picture.

5.  From the base-exposure,  dial back EV -2 stops exposure compensation; e.g., 2 stops under-exposure, and take the first picture.

6.  As rapidly as possible, dial the next exposure (EV -1), followed by EV +0, EV+1, and EV +2.  Be sure the camera is steady between each shot.  When you are done you will have 5 exposures.


See these Image-Liner articles for details on the Exposure:
Auto-Bracketing vs Exposure Compensation
Using an 18% Grey Card
Controlling White Balance


Taking the Frames:

With HDR photography, here are the main rules.
  • It is foolish to not use a tripod
  • Use a RAW format; do not allow compression
  • Objects cannot be moving - this includes clouds, winded foliage, etc.
  • Take three or more exposures at different EV values (bracket).  5 photos seems optimum, if your software supports this many.
  • Take the photos as quickly as possible
  • Out of habit, I start with under-exposures
  • Use EV 0.7 for subtle HDR, Use EV 1.0 for normal, EV 1.5 for dramatic
  • Use Aperture-preferred (not programmed or shutter preferred) so depth-of-field does not shift 
If the wind is blowing and trees and clouds are dancing across the view finder, the HDR will fail. Moving clouds are particularly troublesome because the bright sky is one of the main reasons for using HDR - you want to bring the brightness into range with the foreground -- but their movement causes bizarre pixellations and color shifts in the finished HDR  Even with software trickery, where you can exclude areas from HDR, you will lose the hoped-for dynamic range and you cannot recover from these problems in post-processing.

Because they twitch and sway ever-so-slightly, people also make poor HDR subjects. 

No doubt, shooting JPG at High Quality is convenient but the images are compressed and will compress more aggressively at the -2 and +2 ranges (e.g. more blacks and more whites are more compressible).  For example, look at Frame-1, above.  Lots and lots of black.  When HDR sees these frames, it will detect more changes than expected and will likely introduce artifacts into the combined photo.  For this reason, shoot in RAW.


Post Processing with HDR:

You will need software to process an HDR photo and I recommend Paintshop Pro or Photoshop (CS).  I use Paintshop Pro X5 for my photo editing because the software is relatively inexpensive ($100).  The remaining steps in this article reference that tool, but other software will work similarly. 


Organization

Begin by organizing your work.  Create a folder for the image.  Although this seems like extra work, it is worth the effort when you later return to the same images.  The folder will contain each of the 5 exposures, the final ".HDR" file, the final printable version, and any smaller versions you might send by email or post online and you will likely have 8 to 10 files for one photo.  If you take multiple series of the same subject, give each series its own folder.


To help even further, in post-processing rename the five exposures, appending the exposure-compensation in the name.  For example, my Nikon named the first exposure as "DSC-0312.NEF".  I renamed it as "DSC-0312-2.NEF", where "-2" is two stops under-exposed.

DSC-0312-2.NEF   (-2 stops under-exposed)
DSC-0313-1.NEF   (-1 stops under-exposed)
DSC-0314+0.NEF   (EV +0 normal exposure)

DSC-0315+1.NEF   (+1 stop over-exposed)
DSC-0316+2.NEF   (+2 stops over-exposed)


If bracketing at 0.7EV (or other ranges), I still use the -2 nomenclature, knowing the real values are stored in the EXIF information attached to the image.  But I find it helpful to see this in the file-name.  Sometimes when HDRing, I might toss out the +2 frame if I want to bring down the highlights and the filename makes this easy to identify.


HDR Steps:

PSP has two modes - "Manage" and "Edit."  start in the "Manage" tab to build an HDR. 



1.  From the Manage tab, click the left-navigation's "Collections/Computer" tabs, changing to "Computer."

2. Browse to the folder created for the HDR

3.  On the bottom row, PSP displays thumbnails of the images; this is called the "Organizer."  Note exposures (1 through 5).  Hover the mouse to see the exposure compensation and the entire filename.

4.  Highlight each of the original exposures by clicking the first then shift-click the last (exposures 1 through 5, including +0).  The order does not matter, but it is probably sorted by RAW name, under-exposures to over-exposures.


5.  Choose the "HDR" Menu.

'Other-mouse-click' any of the images, and choose menu "HDR, Exposure Merge" from the context menu.

If the "HDR" option is greyed or unavailable, you have a previous HDR window open in the background. Minimize PSP and dismiss other open PSP windows.

6.  The Left-Navigation shows the initial HDR options, illustrated below,

     a. Choose your camera RAW model/brand - e.g. Nikon, Pentax, etc.
     b. Choose Feature-based or Edge Alignment (see below)
     c. Always choose [x] Auto-crop and
     d. Click the "Align" button


   * If the resulting image is fuzzy, indistinct, out-of focus, return to this step and
     change the Alignment method from 'Feature'-based to 'Edge-detection'. 

   * I generally ignore the custom editing (auto-brush, brush-in, etc.) on the bottom half.

   At the bottom of the navigation panel is a next button.

7.  On the next screen, PSP offers six default adjustments.
     Generally, the 'Presets' should be ignored because they are usually too strange.... 



8.  ...Instead, scroll to the bottom of the dialog and make changes manually, but if one of the presets is interesting, you could start with it as a base.  Often, the horizontal adjustments for Tint and Vibrancy should be adjusted closer to the center than PSP's suggestions.



Adjust until the photo appears as desired.


9.  Optional: Create an HDR File.

At the bottom of the left-nav is an optional button, "Create an HDR".  This builds a special ".hdr" file that holds all of the exposures and the current slider-settings.  Expect the resulting file to be near 100mb if shooting RAW.  Use this file if you want to re-build or revisit the original HDR settings.  I don't consider the file a necessity because the original exposures are still available and could be re-created.  The file is convenient if you intend other editing changes or want to play with different styles.


10.  Click "Process" on the bottom of the Adjustment navigation panel. 

PSP opens another left-nav, allowing for basic photo-editing, such as "Smart Photo Fix".  Choose these options as you would for any normal photograph.  Consider starting with the Smart Photo fix.

11. Clicking "Finish" opens the merged HDR into a standard Editing window.


Troublesome Touch Ups

All photos have troublesome areas and it strikes me as humorous when my mind's eye sees the picture one way but when pulled up on a screen, the camera captured something different. 
Once the HDR has merged and you are presented with a single image, begin your normal darkroom work. 

I noted these obvious problems: 


As usual, I am incapable of leveling a tripod and all the trees lean left.  Tilting the frame a few degrees, using the horizon-leveling tool, stood them vertical.

The green stands of trees in the background was not obvious when I was taking the original pictures and I was pleased when I saw them on-screen -- they gave some hope to an otherwise bleak landscape.  The HDR emphasized these colors more than reality but with this photo, I was not after a literal rendition.  If I were, I would have used the EV +0 photo and would not have bothered with this process. 

Several of the tree's burned bark flaked off, exposing a bright orange bark underneath, much like leopard spots.  They were distracting, even in the original photographs.  I calmed them with some old-fashioned burning.

A featureless, flat sky is the bane of all overcast photographs.  There was some admitted darkroom trickery, adding blue that was never there.  Using PSP's new graduated filter (version X5), I applied a dark blue to the top-third of the image.  This was a subtle effect and I am unapologetic about using it.

Click for larger view

What ever you do, do not fix these problems in the original exposures.  You would have to make the exact change, in the exact same spots in all 5 exposures, which is impractical and somewhat impossible; only make changes after the HDR has merged.


Final Save - Use Great Caution

With the final, edited image, save the file in your native editor's format (in Paint Shop Pro, they are a '.pspImage" extension).  Name this file "something_Final.pspimage".  Photoshop users should save as a .PSD / .PSB image.

When saving this image, be sure to turn off compression.  

For example, PSP compresses its own native file-formats.  In the Save-As menu, click "Options" and turn compression off.  For printing, you really want a full-fidelity image.  Even with no immediate printing plans, you must save an uncompressed image or a lot of the details will be lost.  Of course, turning off compression makes for a sizable file -- with most modern cameras, the file size will be near 90MB per image.  Once compressed, you can never gain the lost information back.  For proof, see this article: JPG Compression

If you are particularly proud of the image, and you want to share it, do a Save-As and create smaller versions suitable for websites and email.  Name these versions "something_Final_Small800x600.jpg" and change to a non-compressed JPG file type.   (Even though you can save JPG non-compressed, be aware it will still severely compress the photo but the space saved, compared to the original file's size, will be negligible.)  When doing this, take great care in not accidentally overwriting the master files with a "Save".


File Save Recommendations
  • Save-As in the editor's native format - e.g., .pspimage, .psd/photoshop
  • Name the file "something_Final.pspimage"
  • In the Save-As options, turn off all compression
  • Save-As a second time and create a "something_Final_Small.jpg" image for mailing.
  • Make no editing changes to any of the original RAW photos
This completes this article on HDR.  Your comments welcomed.

Related articles:
White Balancing
Using an 18% Grey Card

NewPort Bya (Yaquina Bay Bridge)
Highway 21 HDR

JPG Compression

Related Imageliner links:
Jump Creek, Idaho
The Pillars of Rome, Oregon
Frank Church Wilderness, Idaho
Grandview, Idaho