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High Dynamic Range Imaging

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  #1  
Old 29-05-2011
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Join Date: May 2008
Posts: 177
High Dynamic Range Imaging
  

One of the problems even more movies and digital sensors is their ability to render scenes with high contrast. This is characterized by high-lights burned and / or shadows completely blocked, while there, the eye can distinguish many more shades. The sensors have a dynamic effect (the ability to record differences in brightness) rather limited, inherent in the technology. We need in these cases the choice between a high emphasis on exposure-lights, shadows or otherwise. However, there are solutions, but which impose some constraints in terms of shooting. Here we will try to do an overview of HDR photography and its application fields.

First, let's define the term "HDR" or High Dynamic Range. I use these images myself in another field, computer graphics, where the format has emerged in the late 90s, thanks to the work of Paul Debevec. This format is now widely used in OpenEXR (developed by ILM, the famous studio of George Lucas) in rendering and compositing in this area. A pixel of an image is composed of three layers of colors, Red Green Blue, each layer can contain a number of nuances. 8bits in each layer is coded on 8 bits (or 8bpc for Bits Per Channel), or 256 shades of red, green, and blue. Indeed, computers are binary, it has 8 '0 'or '1' for encoding information, or 2 8 = 256 possibilities. Three layers (our R, G, B), we obtain 256 3 = 16,777,216 colors or 24bpp (Bit Per Pixel).

A file is actually a 32bit file 8bpc (24bpp then), but with a fourth layer, called alpha, containing information transparency. For example, a pixel is a pixel 100,100,100,128 dark gray, 50% transparency. This is to clarify, because we do not concern us here in the alpha channel. Digital cameras can take photographs of just a contrast of 1000:1 (ratio between the lowest and highest brightness level of representation), measures a real daylight scene, a contrast ratio of 100,000:1. It is therefore not surprising that dark areas on photos usually really drown in a black area or pull of the sun irradiated areas in white without markings. The camera cannot be such a wealth of information with a photo.

To get a realistic picture of a scene, you have to use a trick. With an exposure range in which the same motif deliberately over-exposed, normally exposed and under exposed images are created, both the drawings in the highlights and details will be kept in the shadows - at various individual images. Thanks to this exposure series can be used together with programs like Photoshop CS2 or Adobe Photomatix Pro HDRsoft a photo with high contrast - image with extremely fine color transitions - create an HDR.

On conventional screens, but is such a HDR image, not to its best advantage. A current monitor is the high contrast of the file is not present, it reduces the scene for output automatically. The same happened when printed on paper. In order to be considered on such so-called low-dynamic-range media (LDR-media) the detail of an HDR scene, it still requires an important second step. With a dynamic range compression (tone mapping) the contrast of the image is reduced controls. The result is a displayable file. This, of course not without losses. The user must decide what is important or can be omitted, for which he has several parameters to control the outcome - see photo gallery of this paragraph.

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Old 29-05-2011
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Join Date: May 2008
Posts: 177
Re: High Dynamic Range Imaging

Software’s for HDRi

There are several programs to assist in transforming photographs into HDR. Photoshop CS2 incorporates this functionality, but without doubt the most known and used for this task is Photomatix . Another option is Artizen HDR . In Article I provides links to tutorials on HDR with different programs.
The free program Luminance HDR 2.0.2 create similar results and can compete in terms of user interface well with the commercial competition.

Who does not remember when HDR is best photographed in the starting material, which can in this article will find many useful tips. Lie photos already finished ready for editing, then you can start directly. After downloading Luminance HDR 2.0.2 have Windows users may still extract additional dll-package in the program directory. In the exe file of the dll version 1.9.2 package is already included. Then the software can be started and is operational.

1. Photomatix :

Photomatix Pro and Photomatix Light are stand-alone programs running on Windows and Mac OS X. A free Lightroom Plug-in makes it possible to access Photomatix Pro directly from Lightroom, if desired. Some of the features of Photomatix are also available as a Filter Plug-in of Photoshop CS2 or higher and an Edit Plug-in of Aperture 2 or higher.

2. Luminance HDR 2.0.2 :

Luminance HDR is a free GUI application and open source software that aims to provide a workflow for HDR imaging.
  • OpenEXR (extension EXR, Linux and Mac OS X).
  • RGBE (extension: hdr).
  • Format TIFF: 16 bits, 32 bis and LogLuv (extension: TIFF).
  • Format RAW image (multiple extensions)
  • Format PFS native.
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  #3  
Old 29-05-2011
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Join Date: May 2008
Posts: 177
Re: High Dynamic Range Imaging

Some Recommended Camera for HDR Images

  • Canon EOS-1D Mark IV -
  • Canon EOS-1DS Mark III
  • EOS Rebel T2i
  • EOS Rebel XSi
  • PowerShot G7
  • PowerShot TX1
  • Nikon D3, D3s, D3x
  • Nikon D300
  • Nikon D2Xs
  • Nikon D200
  • Pentax K110D
  • Fuji Fine Pix HS10
  • Olympus E-620
  • Olympus E-500
  • Sony A900
Some Tips to create HDR Images:

The Design: Moving objects are basically not recommended. For now, HDR image is particularly suitable for a sunset, was because of the dark shadows and the occasional loud colors which one of the eternal sunset at least make enough.

The Camera: The demands on the camera itself is comparatively small: it should have a manual mode, or alternatively, a range bracketing function. Ideally, one sets the white balance to prevent any discoloration. Owners of analog cameras have exceptionally particularly easy.

Series of Images: HDR pictures are characterized mainly by color and detail from, so it is desirable for the aperture set too high, as much as possible to close the aperture. After the aperture was set to start with an extremely underexposed recording (-3.0) and at 3-10 and then goes to a greatly over-exposed images consumption (+3.0) over. The number of images without a limit - usually suffice, however, 3 images, with 5 one is on the safe side. Occasionally there are proponents of the RAW format, it is the raw image is stored directly from the CCD, white balance or sharpening may also have to be done by software from the photographer. As a reward for the effort for the RAW format contains much more image information than for example a jpeg.

Verifying the images: The easiest loads the images on the home computer and then into a slide show (Windows Image Viewer, or Linux or Mac equivalent) and pay attention to possible shifts while the images change. Everything should be fine to go directly to the next step, unless you either delete individual slip or repeat the whole process.

HDR image Software: An HDR image format contains all information from all images. The trial version of Photomatix produces such images in the menu under HDR> Generate without any restrictions. But also work around Photoshop version CS2, with HDR (File> Automate> HDR).

Tone Mapping: This is the real part of the work is to extract the useful picture information from the HDR-Wust. The above Photomatix is just that, but the image is marred in the trial version with watermark. Alternative there is the free Basic version of FDRSoft.

Post-processing
: In most cases, tone mapping already a very useful result to obtain. However, it is useful to change the HDR image in a graphics program to later in brightness and curves. For this, open the image in Photoshop, for example, selects the whole image (Ctrl + A), copied the contents (Ctrl + C) and adds the Copied File> New in a "normal" image. Increasing the contrast is often not necessary, instead, you should adjust the color distribution and experiment with the curves.

Conclusion

The HDR technique allows all areas of the picture are perfectly exposed, even with very different brightness levels and contrasted. This gives details on the entire picture but a single shot has a great contrast between highlights and shadows.

The photos must be combined with particular software. This creates an image the first time such a high contrast having it on a monitor or as an expression cannot be displayed. During the subsequent Tone mapping of the high contrast range is reduced again to the representable range of hues. The HDR photos are impressive in any case, are often also somewhat artificial. I suspect that correspond to the combination of images and the subsequent Tone mapping, not all the steps exactly human vision. During processing, the photographer has also in hand to combine the levels so the result is a realistic picture. Often, but also the slightly surreal touch wanted.
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