Dcraw

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Revision as of 14:17, 25 July 2006

Contents

Intro

From an article by David Coffin:

What is dcraw?

Quite simply, it's an ANSI C program to decode any raw image from any digital camera on any computer running any operating system. It is a unique and vital tool in the world of digital photography.

Thousands of people use dcraw without knowing it, as Bibble, BreezeBrowser, IrfanView, Conceiva, and the Adobe Camera Raw plugin all contain source code from dcraw.

Thanks to Dave Coffin the usage of digital cameras is no longer limited to computers running Windows and MacOS, and thanks to him there is a unique way to extract the full dynamic range from RAW files in one go.

dcraw can write 16 bit per channel image files (on windows PSD files are supported) which contain all the image information of the RAW file in a linear (gamma 1.0) color space.

Alternatives

UFRaw is an easy to use GUI that incorporates dcraw, levels can be adjusted and previewed before saving.

Usage

Windows

You shouldn't be afraid of the command line if you want to use dcraw directly. If you simply call it, it gives you a short syntax help. However, it is easy to integrate it in windows explorer right click menu, once you found your favourite parameter settings:

Create a batch file (prefferable in the folder where dcraw is installed) with the dcraw call looking like this:

dcraw -w -3 %*
pause 

Actual parameters may vary according to your needs. Call dcraw at the command line to get a parameter overview. You might consider using the -n and -m switch and play with the -b setting (values below 1.0) in order to get maximum dynamic range.

Create a link to that batch file and move it to the 'Send to' folder (a subfolder of your user folder on "C:\Documents and Settings" - may be hidden, hence you first must unhide it)

16 bit files with Photoshop

Photoshop users can use this files simply by assign a gamma 1.0 color space (and then convert to working space if needed). A gamma 1.0 color space can be created with following steps:

  • Choose Color Settings from Edit menu.
  • Check Advanced Mode
  • Choose sRGB IEC61966-2.1 from the RGB droplist under Working Space.
  • Choose Custom from the same droplist (very top).
  • In the Custom RGB dialog set Gamma to 1.0 - leave all other values as they are.
  • Enter appropriate name (f.e. sRGB Gamma 1) and leave dialog by pressing Ok.
  • In the Color Settings dialog choose Save RGB from the RGB dropdown list.
  • Give an appropriate name (f.e. sRGB Gamma 1.icc) and save (this might be slightly different for Mac users).
  • Close the Color Settings dialog by pressing Cancel (in order not to choose the new profile as working space.

Even after conversion into a gamma 2.2 working space the images might look dull. Don't worry. If you use them with full 16 bit workflow for panorama creation you wont loose anything. You can adjust levels and contrast in your ready stitched panorama.

Other OS

(someone volunteer?)

16 bit with other Image processors

Users of other operating systems or other image processores can apply a gamma of 2.2 to those linear gamma files produced by dcraw in their favourite 16 bit per channel capable image processor (f.e. Cinepaint on Linux).

Downloading

dcraw was originally developed by Dave Coffin for Linux, it is also available as dcraw for Windows and OS X.

--Erik Krause 10:41, 7 Jul 2005 (EDT)

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