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HDR Photography

Alex Healing Adastral Park Photography Club, 11 th February 2010. HDR Photography. What is Dynamic Range?. For a scene : ratio between the brightest and darkest parts of the scene.  

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HDR Photography

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  1. Alex Healing Adastral Park Photography Club, 11th February 2010 HDR Photography

  2. 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

  3. 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.

  4. A ‘bit’ of conversion 12-bit RAW 8-bit 32-bit HDR 12-bit RAW 8-bit HDR 8-bit 12-bit RAW 8-bit Tone Mapping(Dynamic Range Compression) RAW Conversion(optional) Exposure Blending

  5. Normal Exposure (full-frame metering)

  6. Exposure Bracketing +1 0 -1

  7. HDR Image

  8. Not entirely new • Gustave Le Gray, (1820–1884) Source: http://en.wikipedia.org/wiki/Gustave_Le_Gray

  9. 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, …

  10. 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 • …

  11. HDR Software Source: http://wiki.panotools.org/HDR_Software_overview

  12. 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

  13. 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

  14. 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.

  15. 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!

  16. Tone mapping Source: http://beforethecoffee.wordpress.com/photomatix-tutorial/

  17. Surreal HDR Photo by welshbaloney http://www.flickr.com/photos/welshbaloney/ Photo by aicizzhttp://www.flickr.com/photos/aicizz/

  18. True Tone HDR (TTHDR) Photos by ojaipatrickhttp://www.flickr.com/photos/ojaipatrick/

  19. Some of my shots… … and the reasons for why I shot them

  20. Blown-out Skies

  21. Silhouetted Foreground

  22. Silhouetted Foreground

  23. Nothing right

  24. Outside from inside

  25. Direct Sunlight

  26. Direct Sunlight

  27. Direct Sunlight

  28. Direct Sunlight

  29. Moving Targets

  30. Moving Targets

  31. Moving Targets

  32. Moving Targets

  33. Where are the colours?

  34. Where are the colours?

  35. A dull day?

  36. A dull day?

  37. 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.

  38. 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

  39. 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.

  40. HDR Panorama • Panorama first, then HDR • same effect across whole image

  41. 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.

  42. 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

  43. Thanks! http://www.flickr.com/photos/alexhealing/tags/hdr/ http://www.hdrsoft.com/resources/

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