HDR Photography

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HDR Photography Powered By Docstoc
					Alex Healing
Adastral Park Photography Club, 11th February 2010

HDR Photography
What is Dynamic Range?

For a scene: ratio between the brightest and darkest parts of the scene.
For a camera: ratio of saturation to noise. More specifically, ratio of the
   intensity that just saturates the camera to the intensity that just lifts
   the camera response one standard deviation above camera noise.
For a display: ratio between the maximum and minimum intensities
   emitted from the screen.

The luminance of starlight is around 0.001 cd/m2, that of a sunlit scene
   is around 100,000 cd/m2, which is hundred millions times higher

                                        Source: http://www.hdrsoft.com/resources/dri.html
What is High-Dynamic Range
 Post-processing technique where multiple
   exposures are combined to create a single
   image with higher dynamic range.

 They are 32-bit images (96-bits per colour pixel) with an
  infinite set of values each pixel can take (floating point).
  Standard RAW images are 12-bit and JPEG are 8-bit.
 In order to reproduce the dynamic range on low dynamic
  range displays or prints, the ranges are compressed using by
  tone mapping.
A ‘bit’ of conversion

12-bit      8-bit

12-bit                                                   8-bit
            8-bit                 32-bit HDR
RAW                                                      HDR

                                                Tone Mapping
                                               (Dynamic Range
         RAW Conversion
                          Exposure Blending
Normal Exposure
(full-frame metering)
Exposure Bracketing



HDR Image
Not entirely new

 Gustave Le Gray, (1820–1884)

                      Source: http://en.wikipedia.org/wiki/Gustave_Le_Gray
Why HDR?

 “well… you really had to be there…”
 Film/CCDs are not eyes
   we are under a patchwork illusion all the time
             (but ignorance is bliss)
 Realistic  Surreal
 Increases your photo-taking possibilities
   e.g. eliminate need for fill-in flash for
    indoor/outdoor hybrid shots, direct sunlight, …
What you need

 A (digital) camera
   Preferably capable of auto exposure bracketing
 Ideally a tripod
   (I’ve never used one!)
 HDR software
   Some free, some commercial
 Lots of other optional tools
   Photoshop
   …
HDR Software

     Source: http://wiki.panotools.org/HDR_Software_overview
Taking the photos

 Preferably use a tripod

 Use Automatic Exposure
  Bracketing (AEB) where
                            Source: http://www.usa.canon.com/dlc/controller?act=GetArticleAct&articleID=1646

 Shoot in either JPEG or
  RAW. HDR software can
  handle several RAW
Preparing the photos

 Be aware of any moving subjects
   can remove before to avoid ghosting or do in a
    single step after the HDR image is created
   HDR software may be able to avoid ghosting but
    there will always be cases where it fails
Combining the photos

 HDR software may have
  integral image
  alignment for handheld
 The combined image
  will not display well on
  your monitor however
  until you tone map to
  compress the 32-bit
  image into something
Tone mapping

 Depends what effect you want but if realism
  is what you’re after then you have to be very
   Potential unwanted effects include halos, tone
    reversals, noise and sometimes just too much
Tone mapping   Source: http://beforethecoffee.wordpress.com/photomatix-tutorial/
Surreal HDR

                                Photo by welshbaloney http://www.flickr.com/photos/welshbaloney/

    Photo by aicizz http://www.flickr.com/photos/aicizz/
True Tone HDR (TTHDR)

    Photos by ojaipatrick http://www.flickr.com/photos/ojaipatrick/
Some of my shots…

… and the reasons for why I shot them
Blown-out Skies
Silhouetted Foreground
Silhouetted Foreground
Nothing right
Outside from inside
Direct Sunlight
Direct Sunlight
Direct Sunlight
Direct Sunlight
Moving Targets
Moving Targets
Moving Targets
Moving Targets
Where are the colours?
Where are the colours?
A dull day?
A dull day?
Exposures and how many?

 Spot metering on the highlights and shadows,
  note the exposure times.
 Multiply exposure time for highlights by four
  successively (stop spacing of 2 EV) until you pass
  the exposure time for the shadows.
 Three exposures with 2 EV is typically good but
  you may have to go to full manual depending on
  your camera model.
Remember your settings

 Settings should remain constant for all the
  images in a series
   Focus
   Aperture (set small)
   ISO (set as low as possible, particular if using tripod)
   Auto white balancing (beware but impact minimised)
     Custom white balance or shoot in RAW

 Not strictly HDR but using a good RAW
  converter you can create fake exposures which
  sometimes squeeze more data out than you
  would otherwise with a single image.
   Due to good noise reduction
 Dynamic range is essentially the same though as
  you’re simply splitting the dynamic range of a
  single RAW image (12-bits per colour) into slices
  and then recombining.
HDR Panorama

 Panorama first, then HDR
   same effect across whole image

 Re introduce originals to make more realistic
  and get rid of any ghosting.

 De-noising further.

 HDR software can be very powerful but there
  may be times that you’d prefer touching up
  further with what you’re familiar with.
HDR in conclusion

 Diverse: ultra-realistic to shockingly surreal
   Personal taste but think about what your aims are
 Don’t use for the sake of it
   If the scene lends itself to higher dynamic range,
    otherwise many other post-processing techniques
    that might be more suitable
 Go play, either casually or more seriously
   Doesn’t take long to get results and there is an
    element of exploration and discovery in the tone
    mapping process in particular