HDRI (High Dynamic Range Images)

Is a technic that allows a far greater dynamic range of exposures than a normal photo can show.(i.e. there is a wider range of values between light and shadows) This technic is used in computergraphics and photography and can show far more details than a normal photo.
The intention of HDRI is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to the deepest shadows.

When HDRI was developed it was for the use of computer games this is why computer games where far different to the look of a photo. Now a days we are able to create HDRI out of photos too to show the high range of exposure we saw.
With the rising popularity of digital cameras and easy to use desktop software, the term "HDR" is now popularly used to refer to the process of tone mapping together with bracketed exposures of normal digital images, giving the end result a high, often exaggerated dynamic range. Tone mapping is also used to display HDR images on devices with a low native dynamic range, such as a computer screen. Normal screens are not able to show such a high range therefore it will be converted in a LDRI. (Low dynamic range image)


History
The technic has been developed by Paul Debevec. His aim was to create a technic to show realistic light and animated computer graphic objects, thus he developed HDRI maps. In 1985 the most common HDRI format the RGBE image has been created by Gregory Ward.


Comparison with traditional digital images
Information stored in high dynamic range images usually corresponds to the physical values of luminance or radiance that can be observed in the real world. This is different from traditional digital images, which represent colors that should appear on a monitor or a paper print. Therefore, HDR image formats are often called "scene-referred", in contrast to traditional digital images, which are "device-referred" or "output-referred". Furthermore, traditional images are usually encoded for the human visual system (maximizing the visual information stored in the fixed number of bits), which is usually called "gamma encoding" or "gamma correction". The values stored for HDR images are often linear, which means that they represent relative or absolute values of radiance or luminance (gamma 1.0).
HDR images require a higher number of bits per color channel than traditional images.


Tone mapping
One problem with HDR has always been in viewing the images. CRTs, LCDs, prints, and other methods of displaying images only have a limited dynamic range.
Thus various methods of "converting" HDR images into a viewable format have been developed, generally called "tone mapping".
Early methods of tone mapping were simple. They simply showed a "window" of the entire dynamic range, clipping to set minimum and maximum values. However, more recent methods have attempted to show more of the dynamic range.



Software
Photomatix Pro 2.5.1 [link]
Picturenaut HDRI Generator/Tone-Mapping [link]
FDRTools Basic [link]
Photoshop since version CS2


What you have to do to create your own HDRI
First of all you need a camera which you can use in the M mode (manuell) thus you can change the shutter speed on your own.

First you chose the lens you want to have. I hope you already know which F Number has which effect. The other thing you need is a tripod which allows you to keep the motive constant.

Now arrange your tripod and choose your motive. Now you start taking the shots and changing you shutter speed so you have pics really bright, really dark, and between this.
Don’t be afraid to do too much shots. Now you take these shots and combine them in one of the softwares above. How the software works is different but will be explained.


Examples for HDRI



I hope you liked this explanation for the HDRI technic.

Please support it if you liked it to spread the word and enrich artists.

Thanks for reading =Alderman

_{Parts of this article where used from wikipedia. There you find a even more details article to the topic}