HDR Photography
description
Transcript of HDR Photography
Alex HealingAdastral Park Photography Club, 11th February 2010
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 Photography?
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 RAW
12-bit RAW
12-bit RAW
8-bit
32-bit HDR 8-bit HDR8-bit
8-bit
RAW Conversion(optional)
Exposure Blending
Tone Mapping(Dynamic
Range Compression)
Normal Exposure(full-frame metering)
Exposure Bracketing
+1
0
-1
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 possible
Shoot in either JPEG or RAW. HDR software can handle several RAW formats.
Source: http://www.usa.canon.com/dlc/controller?act=GetArticleAct&articleID=1646
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 photos.
The combined image will not display well on your monitor however until you tone map to compress the 32-bit image into something renderable.
Tone mapping
Depends what effect you want but if realism is what you’re after then you have to be very careful. Potential unwanted effects include halos,
tone reversals, noise and sometimes just too much colour!
Tone mappingSource: 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
RAW ‘HDR’
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
Post-post-processing
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
Thanks!
http://www.flickr.com/photos/alexhealing/tags/hdr/
http://www.hdrsoft.com/resources/