Difference between revisions of "HDR"

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HDR or HDRI refers to techniques and images that are capable of taking or showing higher [[dynamic range]] as usual photography and imaging. True HDR images use a higher bit depth and/or floating point format in order to extend the range of values. There are several HDR formats among them  
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HDR means High Dynamic Range. The term is used to refer to techniques and images that are capable of capturing and reproducing scenes with a high [[dynamic range]].
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HDR is used more or less accurately for almost any way to get more details out of the shadows and/or highlights. To understand how so-called "HDR techniques" work, it is important to differentiate between the two limitations that affects dynamic range in photography and imaging. The first limitation comes from the capture, i.e. the camera. The second limitation from the display, i.e. monitor or printer.
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* <b>Camera</b> limitation: Standard digital cameras can capture at most a [[dynamic range]] of 1,000:1, which is much less than the dynamic range of most outdoor scenes. This limitation is usually addressed by taking several exposures of the same scene (this is the purpose of the "Automatic Exposure Bracketing" function available in many digicams).
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* <b>Display</b> limitation: Standard monitors have a rather low dynamic range, around 100:1, which is not even enough to display correctly the RAW data captured by a standard camera. This limitation is addressed by [[tone mapping]] or by techniques that directly blend exposures. Exposure Blending can be done either manually in Photoshop, semi-manually with Photoshop actions (see [[Contrast Blending]] and Jook Leung's [http://360vr.com/HDRforDummies HDR for Dummy]) or automatically in specialized software (see [http://www.hdrsoft.com Photomatix]).
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Both camera and display limitations can be overcome with specialised equipment like the [http://spheron.com/spheron/public/en/hdri_spherocamhdr/hdri_spherocamhdr.php SpheroCam HDR] camera and [http://www.brightsidetech.com/ Brightside HDR Display]. However, such equipment remains very expensive for the time being.
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HDR images are stored in a high bit depth and/or floating point format. There are several HDR formats among them  
 
* .hdr Radiance format
 
* .hdr Radiance format
 
* .tif Floating point TIFF
 
* .tif Floating point TIFF
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* .exr OpenEXR format
 
* .exr OpenEXR format
  
Some more info on HDR is found on wikipedia: [http://en.wikipedia.org/wiki/High_dynamic_range_imaging]
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Some more info on HDR is found on wikipedia: [http://en.wikipedia.org/wiki/High_dynamic_range_imaging] and the [http://www.hdrsoft.com/resources/dri.html HDR Image FAQ].
  
HDR is used more or less accurately for almost any way to get more details out of the shadows and/or highlights. True HDR is only possible by [[Contrast Blending]] (see there for details) or specialised equipment like HDR cameras (f.e. [http://spheron.com/spheron/public/en/hdri_spherocamhdr/hdri_spherocamhdr.php SpheroCamHDR]) or HDR Monitors.
 
 
[[Category:Glossary]]
 
[[Category:Glossary]]

Revision as of 13:06, 25 December 2005

HDR means High Dynamic Range. The term is used to refer to techniques and images that are capable of capturing and reproducing scenes with a high dynamic range.

HDR is used more or less accurately for almost any way to get more details out of the shadows and/or highlights. To understand how so-called "HDR techniques" work, it is important to differentiate between the two limitations that affects dynamic range in photography and imaging. The first limitation comes from the capture, i.e. the camera. The second limitation from the display, i.e. monitor or printer.

  • Camera limitation: Standard digital cameras can capture at most a dynamic range of 1,000:1, which is much less than the dynamic range of most outdoor scenes. This limitation is usually addressed by taking several exposures of the same scene (this is the purpose of the "Automatic Exposure Bracketing" function available in many digicams).
  • Display limitation: Standard monitors have a rather low dynamic range, around 100:1, which is not even enough to display correctly the RAW data captured by a standard camera. This limitation is addressed by tone mapping or by techniques that directly blend exposures. Exposure Blending can be done either manually in Photoshop, semi-manually with Photoshop actions (see Contrast Blending and Jook Leung's HDR for Dummy) or automatically in specialized software (see Photomatix).

Both camera and display limitations can be overcome with specialised equipment like the SpheroCam HDR camera and Brightside HDR Display. However, such equipment remains very expensive for the time being.

HDR images are stored in a high bit depth and/or floating point format. There are several HDR formats among them

  • .hdr Radiance format
  • .tif Floating point TIFF
  • .pfm Portable floatmap
  • .float Raw binary floating point
  • .exr OpenEXR format

Some more info on HDR is found on wikipedia: [1] and the HDR Image FAQ.